Third Edition

Tutorial Texts Series

• Practical Applications of Infrared Thermal Sensing and Imaging Equipment, Third Edition, Herbert
Kaplan, Vol. TT75
• Bioluminescence for Food and Environmental Microbiological Safety, Lubov Y. Brovko, Vol. TT74
• Introduction to Image Stabilization, Scott W. Teare, Sergio R. Restaino, Vol. TT73
• Logic-based Nonlinear Image Processing, Stephen Marshall, Vol. TT72
• The Physics and Engineering of Solid State Lasers, Yehoshua Kalisky, Vol. TT71
• Thermal Infrared Characterization of Ground Targets and Backgrounds, Second Edition, Pieter A. Jacobs,
Vol. TT70
• Introduction to Confocal Fluorescence Microscopy, Michiel Müller, Vol. TT69
• Artificial Neural Networks An Introduction, Kevin L. Priddy and Paul E. Keller, Vol. TT68
• Basics of Code Division Multiple Access (CDMA), Raghuveer Rao and Sohail Dianat, Vol. TT67
• Optical Imaging in Projection Microlithography, Alfred Kwok-Kit Wong, Vol. TT66
• Metrics for High-Quality Specular Surfaces, Lionel R. Baker, Vol. TT65
• Field Mathematics for Electromagnetics, Photonics, and Materials Science, Bernard Maxum, Vol. TT64
• High-Fidelity Medical Imaging Displays, Aldo Badano, Michael J. Flynn, and Jerzy Kanicki, Vol. TT63
• Diffractive Optics–Design, Fabrication, and Test, Donald C. O’Shea, Thomas J. Suleski, Alan D.
Kathman, and Dennis W. Prather, Vol. TT62
• Fourier-Transform Spectroscopy Instrumentation Engineering, Vidi Saptari, Vol. TT61
• The Power- and Energy-Handling Capability of Optical Materials, Components, and Systems, Roger M.
Wood, Vol. TT60
• Hands-on Morphological Image Processing, Edward R. Dougherty, Roberto A. Lotufo, Vol. TT59
• Integrated Optomechanical Analysis, Keith B. Doyle, Victor L. Genberg, Gregory J. Michels, Vol. TT58
• Thin-Film Design Modulated Thickness and Other Stopband Design Methods, Bruce Perilloux, Vol. TT57
• Optische Grundlagen für Infrarotsysteme, Max J. Riedl, Vol. TT56
• An Engineering Introduction to Biotechnology, J. Patrick Fitch, Vol. TT55
• Image Performance in CRT Displays, Kenneth Compton, Vol. TT54
• Introduction to Laser Diode-Pumped Solid State Lasers, Richard Scheps, Vol. TT53
• Modulation Transfer Function in Optical and Electro-Optical Systems, Glenn D. Boreman, Vol. TT52
• Uncooled Thermal Imaging Arrays, Systems, and Applications, Paul W. Kruse, Vol. TT51
• Fundamentals of Antennas, Christos G. Christodoulou and Parveen Wahid, Vol. TT50
• Basics of Spectroscopy, David W. Ball, Vol. TT49
• Optical Design Fundamentals for Infrared Systems, Second Edition, Max J. Riedl, Vol. TT48
• Resolution Enhancement Techniques in Optical Lithography, Alfred Kwok-Kit Wong, Vol. TT47
• Copper Interconnect Technology, Christoph Steinbrüchel and Barry L. Chin, Vol. TT46
• Optical Design for Visual Systems, Bruce H. Walker, Vol. TT45
• Fundamentals of Contamination Control, Alan C. Tribble, Vol. TT44
• Evolutionary Computation Principles and Practice for Signal Processing, David Fogel, Vol. TT43
• Infrared Optics and Zoom Lenses, Allen Mann, Vol. TT42
• Introduction to Adaptive Optics, Robert K. Tyson, Vol. TT41
• Fractal and Wavelet Image Compression Techniques, Stephen Welstead, Vol. TT40
• Analysis of Sampled Imaging Systems, R. H. Vollmerhausen and R. G. Driggers, Vol. TT39
• Tissue Optics Light Scattering Methods and Instruments for Medical Diagnosis, Valery Tuchin, Vol. TT38
• Fundamentos de Electro-Óptica para Ingenieros, Glenn D. Boreman, translated by Javier Alda, Vol. TT37
• Infrared Design Examples, William L. Wolfe, Vol. TT36
• Sensor and Data Fusion Concepts and Applications, Second Edition, L. A. Klein, Vol. TT35
• Practical Applications of Infrared Thermal Sensing and Imaging Equipment, Second Edition, Herbert
Kaplan, Vol. TT34
• Fundamentals of Machine Vision, Harley R. Myler, Vol. TT33
 Third Edition

Tutorial Texts in Optical Engineering

Volume TT75

Bellingham, Washington USA

Library of Congress Cataloging-in-Publication Data

Kaplan, Herbert.
Practical applications of infrared thermal sensing and imaging equipment / by Herbert
Kaplan. — 3rd ed.
p. cm. — (Tutorial texts)
Includes bibliographical references.
ISBN 978-0-8194-6723-2
1. Thermography. 2. Infrared imaging. 3. Infrared detectors. 4. Infrared equipment.
5. Thermography. 6. Infrared technology. I. Title.

TA1570.K37 2007
621.36'2—dc22
2007004303

Published by

SPIE
P.O. Box 10
Bellingham, Washington 98227-0010 USA
Phone: +1 360 676 3290
Fax: +1 360 647 1445
Email: spie@spie.org
Web: http://spie.org

Copyright © 2007 The Society of Photo-Optical Instrumentation Engineers

All rights reserved. No part of this publication may be reproduced or distributed

in any form or by any means without written permission of the publisher.

The content of this book reflects the work and thought of the author(s).
Every effort has been made to publish reliable and accurate information herein,
but the publisher is not responsible for the validity of the information or for any
outcomes resulting from reliance thereon.

Printed in the United States of America.

 Introduction to the Series
Since its conception in 1989, the Tutorial Texts series has grown to more than 70
titles covering m any diverse fields of science and engineering. When the series
was st arted, the goal of the serie s wa s to provide a way to m ake the material
presented in SPIE short c ourses available to those who could not attend, and to
provide a reference text for those who could. Many of the texts i n this series are
generated from notes that were presen ted during these short courses. But as
stand-alone documents, short course no tes do not generally serve the student o r
reader w ell. Short course notes typically are developed on the assu mption that
supporting material will b e presented verb ally to com plement the notes, which
are generally written in summary form to highlight key technical topics and
therefore ar e not intended as stand-alone documents. Additionally, the figures,
tables, and other graphically form atted informati on acco mpanying the notes
require the further explan ation given during the in structor’s lecture. Thus, by
adding the appropriate detail presented during the lecture, the course material can
be read and used independently in a tutorial fashion.

What separates the books in this series fro m other technical monographs and
textbooks is the way in wh ich the material is presented. To keep i n line with th e
tutorial nature of the seri es, many of the topics presented in t hese texts are
followed by detailed examples that further explain the concepts presented. Many
pictures and illustrations are included with each text and, where appropriate,
tabular reference data are also included.

The topics within the series have grown fro m the initial areas of geometri cal
optics, optical detectors, and image pro cessing to in clude the e merging fields of
nanotechnology, biomedical optics, and micromachining. When a proposal for a
text is r eceived, each proposal is evaluated to deter mine the rel evance of th e
proposed topic. This initial reviewing process has been ve ry helpful to authors in
identifying, early in the writing process, the need for additional material or other
changes in approach that would serve to strengthen the text. Once a manuscript is
completed, it is peer reviewed to ensure that chapters communicate accurately the
essential ingredients of the processes and technologies under discussion.

It is m y goal to m aintain the sty le an d qualit y of b ooks in the s eries, and to

further expand the topic areas to include new emerging fields as they become of
interest to our reading audience.

Arthur R. Weeks, Jr.

University of Central Florida
Contents

List of Figures xiii

List of Tables xvii
List of Acronyms and Abbreviations xix
Preface xxi

Part I: Basics and Instrument Overview

Chapter 1 Introduction 3
1.1 Overview of This Text 3
1.2 Reasons for Using IR Instruments 3
1.3 Advantages of Noncontact Thermal Measurement 4
1.4 Some Historical Background 5
1.5 Evolution of IR Cameras 6

Chapter 2 Basics of Noncontact Thermal Measurements 9

2.1 Heat Transfer and Radiation Exchange Basics 9
2.1.1 Heat and temperature 9
2.1.2 Converting temperature units 9
2.1.3 Three modes of heat transfer 10
2.1.4 Conduction 10
2.1.5 Convection 11
2.1.6 Radiation 12
2.1.7 Radiation exchange at the target surface 13
2.1.8 Specular and diffuse surfaces 14
2.1.9 Transient heat exchange 14
2.2 Infrared Measurement Problem 15
2.2.1 Noncontact thermal measurements 16
2.2.2 Target surface 16
2.2.3 Transmitting medium 20
2.2.4 Measuring instrument 22
2.3 Thermal Scanning and Imaging Instruments 25
2.3.1 Line scanning 25
2.3.2 Two-dimensional opto-mechanical scanning 26

vii
viii Contents

2.3.3 Infrared focal plane array (IRFPA) cameras 27

2.3.4 IRFPA detectors 28
2.3.5 Pyroelectric vidicon thermal imagers 29

Chapter 3 Matching the Instrument to the Application 33

3.1 Radiation Thermometers (Point-Sensing Instruments) 33
3.2 Infrared Cameras—Qualitative and Quantitative 37
3.2.1 Performance parameters of quantitative cameras 39
3.2.1.1 Total field of view (TFOV) and instantaneous
field of view (IFOV) 40
3.2.1.2 Temperature sensitivity: MRTD or MRT 40
3.2.1.3 Imaging spatial resolution and instantaneous
FOV 41
3.2.1.4 Measurement spatial resolution (IFOVmeas
or MFOV) for opto-mechanically scanned imagers 43
3.2.1.5 Measurement spatial resolution (IFOVmeas
or MFOV) for FPA imagers 45
3.2.1.6 Speed of response and frame repetition rate 45
3.2.2 Performance parameters of qualitative cameras 46
3.3 Thermal Imaging Software 46
3.4 Thermal Image Fusion Techniques 48

Chapter 4 Instruments Overview 49

4.1 Introduction and Classification of Instruments 49
4.2 Instrument Manufacturers 50
4.3 Discussion of Instruments 50
4.3.1 Point sensors (radiation thermometers) 50
4.3.1.1 Infrared thermocouples and probes 50
4.3.1.2 Portable hand-held instruments 51
4.3.1.3 On-line monitoring and control 52
4.3.1.4 Special instruments 52
4.3.2 Line scanners 53
4.3.3 Infrared cameras (thermal imagers) 54
4.3.3.1 Cameras, nonmeasuring (thermal viewers) 54
4.3.3.2 Cameras, measuring (thermographic imagers) 55
4.3.3.3 Performance comparisons of FPA measuring
cameras 56
4.4 Thermal Imaging Diagnostic Software 57
4.4.1 Quantitative thermal measurements of targets 58
4.4.2 Detailed processing and image diagnostics 59
4.4.3 Image recording, storage, and recovery 59
4.4.4 Image comparison 60
4.4.5 Thermal image fusion 60
4.4.6 Report and database preparation 61
Contents ix

Chapter 5 Using IR Sensing and Imaging Instruments 63

5.1 Introduction: The Thermal Behavior of the Target 63
5.1.1 Emissivity difference 64
5.1.2 Reflectance difference 64
5.1.3 Transmittance difference 64
5.1.4 Geometric difference 64
5.1.5 Mass transport difference 65
5.1.6 Phase-change difference 65
5.1.7 Thermal capacitance difference 65
5.1.8 Induced heating difference 65
5.1.9 Energy conversion difference 65
5.1.10 Direct heat transfer difference 65
5.1.11 Learning about the target environment 66
5.2 Preparation of Equipment for Operation 66
5.2.1 Calibration and radiation reference sources 66
5.2.1.1 Checking calibration 67
5.2.1.2 Transfer calibration 67
5.2.2 Equipment checklist 68
5.2.3 Equipment checkout and calibration 68
5.2.4 Batteries 68
5.3 Avoiding Common Mistakes in Instrument Operation 68
5.3.1 Start-up procedure 69
5.3.2 Memorizing the default values 69
5.3.3 Setting the correct emissivity 69
5.3.4 Filling the IFOVmeas for accurate temperature
measurements 70
5.3.5 Aiming normal to the target surface 71
5.3.6 Recognizing and avoiding reflections from external
sources 71
5.3.7 Avoiding radiant heat damage to the instrument 72
5.3.8 Using IR transmitting windows 72
5.4 The Importance of Operator Training 72
5.4.1 Training programs and certification 72

Part II: Instrument Applications

Chapter 6 Introduction to Applications 77

Chapter 7 Plant Condition Monitoring and Predictive Maintenance 79

7.1 Introduction 79
7.2 Electrical Findings 80
7.2.1 High electrical resistance 80
7.2.2 Short circuits 80
x Contents

7.2.3 Open circuits 82

7.2.4 Inductive currents 83
7.2.5 Energized grounds 83
7.2.6 Condition guidelines 84
7.3 Mechanical Findings 85
7.3.1 Friction 85
7.3.2 Valve or pipe blockage/leakage 86
7.3.3 Insulation within the plant or facility 87
7.4 Miscellaneous Applications 87
7.4.1 Rebar location 88
7.4.2 Condenser air in-leakage 88
7.4.3 Containment spray ring headers 88
7.4.4 Hydrogen igniters 88
7.4.5 Effluent thermal plumes 89
7.4.6 Gas leak detection 89
7.4.7 Seal failures 89

Chapter 8 Buildings and Infrastructure 91

8.1 Introduction 91
8.2 Measuring Insulating Properties 92
8.3 Considering the Total Structure 92
8.4 Industrial Roof Moisture Detection 93
8.5 Subsurface Leaks and Anomalies 94
8.6 Thermal Image Fusion Benefit 96
8.7 Thermographic Inspection of Our Aging Infrastructure 96

Chapter 9 Materials Testing 97

9.1 Materials Testing—IR Nondestructive Testing 97
9.2 Failure Modes and Establishment of Acceptance Criteria 99
9.3 Selecting the Right IR Imaging System 99
9.4 Pulsed Heat Injection Applications 101
9.4.1 New signal-based technique simplifies image
interpretation 103
9.4.2 Case study: Boiler tube corrosion thinning assessment 103
9.5 Infrastructure NDT 106

Chapter 10 Product and Process Monitoring and Control 107

10.1 Evolution of Noncontact Process Control 107
10.2 Full Image Process Monitoring 109
10.3 Product Monitoring of Semiconductors 110
10.4 Steel Wire Drawing Machine Monitoring 110
10.5 Glass Products Monitoring (Spectral Considerations) 112
10.6 Full Image Process Control 112
10.7 Closing the Loop—Examples 114
Contents xi

Chapter 11 Night Vision, Security, and Surveillance 117

11.1 Introduction 117
11.2 Comparing Thermal Imagers with Image Intensifiers 118
11.3 Homeland Security and other Nonmilitary Applications 118
11.3.1 Aerial-, ground-, and sea-based search and rescue 118
11.3.2 Firefighting and first response 118
11.3.3 Space and airborne reconnaissance 119
11.3.4 Police surveillance and crime detection and security 119
11.3.5 Driver’s aid night vision 120
11.3.6 New thermal image fusion applications 121
11.3.7 New military applications 121

Chapter 12 Life Sciences Thermography 123

12.1 Introduction 123
12.2 Thermography as a Diagnostic Aid in the Early Detection
of Breast Cancer 123
12.3 Veterinary Medicine 124
12.4 Biological and Threat Assessment Applications 124

Appendix A Commercial Instrument Performance Characteristics 127

Appendix B Manufacturers of IR Sensing and Imaging Instruments 145
Appendix C Table of Generic Normal Emissivities of Materials 149
Appendix D A Glossary of Terms for the Infrared Thermographer 155
List of Figures

Figure Description Page

2.1 Conductive heat flow 11

2.2 Convective heat flow 12
2.3 Infrared in the electromagnetic spectrum 13
2.4 Radiative heat flow 13
2.5 Radiation impinging on a surface 14
2.6 Three sets of characteristics in making IR measurements 17
2.7 Blackbody curves at various temperatures 17
2.8 Spectral distributions of a blackbody, graybody,
and non-graybody 19
2.9 Components of energy reaching the measuring instrument 19
2.10 Aiming the instrument to avoid point reflections 20
2.11 Infrared atmospheric transmission for a 10-meter path
at sea level (50% relative humidity) 21
2.12 Spectral characteristics of glass samples (percent transmission,
absorption, and reflectance) 21
2.13 Transmission of IR transmitting materials 22
2.14 Components of an IR radiation thermometer 23
2.15 Typical IR radiation thermometer schematic 24
2.16 Response curves of various IR detectors 25
2.17 (a) The addition of a scanning element to a radiation thermo-
meter for single line scanning. (b) Eliminating the scanning
element – the substitution of a linear FPA detector for
the single element detector 26
2.18 Infrared line scanner schematic and scanner operation 27
2.19 Infrared opto-mechanical scanning imager 27
2.20 Infrared focal plane array camera schematic 28
2.21 Pyrovidicon camera tube schematic 29
3.1 Instrument speed of response and time constant 34
3.2 Instrument FOV determination 35
3.3 Fields of view of IR radiation thermometers 36
3.4 Measuring temperature of polyethylene 38
3.5 Measuring temperature of polyester 38
3.6 TFOV and IFOV of an IR camera 41

xiii
xiv List of Figures

Figure Description Page

3.7 Test setup for MRTD measurement and MRTD curve 42

3.8 Test setup for MTF measurement 42
3.9 MRTD and MTF for a system rated at 1 mrad 44
3.10 Test setup for slit response function 44
3.11 Hole response method for determination of IFOVmeas
(MFOV) for FPA-based cameras 45
3.12 Plot of hole response function for an FPA-based camera
where MFOV is measured at 8.2 mrad 46
5.1 Measuring target effective emissivity 70
5.2 Quick calculation for target spot size and IFOV calculation 71
7.1 Excessive heating of a connecting clip due to deterioration 81
7.2 Overheating at a switchyard disconnect due to high contact
resistance 81
7.3 Disastrous failure of leaking isolator 82
7.4 Fusion of a visible and thermal image of a complex
electrical panel 83
7.5 Overheated pump motor at right caused by lubricant
deterioration 86
7.6 Abnormally functioning steam trap shown on the left side 87
7.7 Gas leak in valve appears as a black cloud on the thermogram 89
7.8 Leaking seal in a joint between a gas turbine and a steam
boiler 90
8.1 Thermogram of a building showing the effects of air
exfiltration 92
8.2 Thermogram of a building showing the effects of insulation
deficiencies 93
8.3 Thermogram of a roof with moisture saturation 95
8.4 Roof thermogram with heated interior showing insulation
differences and no water saturation 95
8.5 Photo and thermogram of a radiantly heated floor 95
8.6 Insulation void on visibly featureless wall is pinpointed using
thermal image fusion 96
9.1 Example of steady-state, active (heat injection) IRNDT for
occlusion and void detection 99
9.2 Three-view thermogram of a cable section with electrical
current used as the active heat source 100
9.3 Basis for time-resolved IR radiometry (TRIR) 101
9.4 Configuration for pulsed thermography 103
9.5 Examples of IRNDT images using thermal wave injection—
see text for descriptions 104
9.6 Results of thermal image reconstruction on a graphite epoxy
sample 104
List of Figures xv

Figure Description Page

9.7 In-situ thermogram of a boiler tube section indicating areas

of thinning due to corrosion 105
9.8 Thermogram of a new section of boiler tubing not yet put
into service—no thinning indicated 105
10.1 Three methods of accomplishing process control 108
10.2 Typical configuration for multisensor process control 108
10.3 Electrolytic tankhouse scan where interelectrode shorts
appear as hot spots 109
10.4 Quadrant display of a device under test showing
(a) unpowered radiance, (b) powered radiance, (c) emissivity,
and (d) “true temperature” 111
10.5 Wire drawing machine capstan thermograms showing
(a) proper cooling, and (b) improper cooling 111
10.6 Using the same imager with different filters to measure
temperatures of the filaments (top thermogram) and
the glass envelope (bottom thermogram) 113
10.7 Thermal image process control using a line scanner
and set points 114
10.8 Full image process control using a line scanner and
multiple zones: (a) before implementation of full image
process control; (b) after implementation of full image process
control 115
11.1 Thermogram of a vessel at sea at night in fog (8–12 µm) 119
11.2 Thermogram of an intruder at night (8–12 µm) 120
11.3 Hidden compartment in a vehicle 120
11.4 Driver’s thermal image compared to visible image 121
11.5 Thermogram of freeway traffic at night (8–12 µm) 122
11.6 (a) Visible, (b) thermal, and (c) fused images with smoke 122
11.7 View of a military helicopter from the ground 122
12.1 Sample breast thermograms of three patients:
(a) normal, (b) fibrosystic changes, and (c) early stage
malignant tumor 124
12.2 Confirmed inflammations at two different locations on
a dog’s back 124
12.3 Thermographic results of SARS screening:
(a) normal subject, and (b) febrile subject 125
A-1 Target and instrument background 156
List of Tables

Table Description Page

2.1 Temperature conversion chart 30

6.1 Industrial applications of thermal sensing and imaging
instruments by industry 77
6.2 Industrial applications of thermal sensing and imaging
instruments by discipline 78
7.1 Classification of electrical faults 84
7.2 Compensating for wind effects 85

xvii
List of Acronyms
and Abbreviations

ANSI American National Standards Institute

ASHRAE American Society of Heating, Refrigerating, and
Air-Conditioning Engineers
ASNT American Society for Nondestructive Testing
ASTM American Society for Test and Measurement
BCD binary coded decimal
BST barium–strontium–titanate
dc emf direct current electromagnetic force
emf electromagnetic force
EPRI Electric Power Research Institute
FLIR forward-looking infrared
FOV field of view
FPA focal plane array
HRSG heat recovery steam generator
IFOV instantaneous field of view
IFOVmeas or MFOV measurement IFOV or measurement spatial resolution
IR infrared
IRFPA infrared focal plane array
IRNDT infrared nondestructive testing
IVD intervertebral disk disease
LWIR long-wave infrared region
MFOV see IFOVmeas
MRT minimum resolvable temperature
MRTD minimum resolvable temperature difference
MTF modulation transfer function
MWIR mid-wave infrared region
NDE nondestructive evaluation
NEI noise equivalent irradiance
NETD noise equivalent temperature difference
NIR near infrared
NIST National Institute of Standards and Technology (U.S.)
P proportional

xix
xx List of Acronyms and Abbreviations

PCMCIA Personal Computer Memory Card International Association

PI proportional plus integral
PID proportional plus integral plus differential
QWIP quantum well infrared photodetector
SRF slit response function
SWIR short-wave infrared region
TE thermoelectric
TFOV total field of view
TLV thermal light valve
TRIR time-resolved infrared radiometry
TSR thermographic signal reconstruction
VDC volts DC
Preface

The mapping of infrared (IR) energy radiated from the surface of natural and manu-
factured objects makes it possible to detect and recognize objects in the dark and
under adverse weather and atmospheric conditions. Quantification of this energy
allows users (thermographers) to determine the temperature and thermal behavior
of objects.
Infrared thermal sensing and imaging instruments make it possible to measure
and map surface temperature and thermal distribution passively and nonintrusively.
In addition to the passive measurement of temperature distribution, thermographers
have learned to use active or “thermal injection” techniques to study and evaluate
the structural integrity of materials and fabricated bonds.
The purposes of this text are:

· To familiarize potential users of commercial IR sensing and imaging instru-

ments with IR measurement and analysis basics;
· To provide the practical information needed for users to select the instrument
most appropriate for their application;
· To describe how to perform valid and successful measurements in a variety of
applications;
· To serve as a reference to help thermographers examine the validity of new ap-
plications.

This text is presented in two parts.

Part I begins with a review of temperature, heat, and heat transfer, with emphasis
on radiative heat transfer and its relationship to IR radiation and measurement ba-
sics. Physical laws (equations) are presented in terms of their practical importance
to the measurement mission.
This is followed by a review and discussion of the characteristics and perfor-
mance parameters of IR sensing and imaging instruments, including a review of
thermal imaging diagnostic software. A discussion of equipment operation follows,
including guidelines for making successful measurements.
Part I concludes with a section on training and training programs, highlighting
the importance of formal operator training and certification.

xxi
xxii Preface

What’s New?
The second edition of this text was published in 1999, and since that time many im-
provements have taken place in instrumentation performance and versatility. For
example, the almost total replacement of opto-mechanically scanned imagers with
focal plane array (FPA)-based “staring” imagers has reduced the size, increased the
ruggedness, and improved the spatial resolution of IR cameras, all of which have
changed thermographers’ expectations of camera performance.
Thus, this third edition reviews these many changes and how they impact the
way thermographers operate, deploy, calibrate, and test the new instruments. In ad-
dition, the instruments that have been made essentially obsolete are reviewed as
part of the historical evolution of the technology.

Part II introduces typical applications for thermal sensing and imaging instru-
ments. Several chapters present various applications areas and discuss typical solu-
tions to measurement problems.
The applications are grouped into logical categories following the guidelines
established by SPIE’s evolving Thermosense series of meetings, held annually
since 1978.
In an attempt to classify these applications into logical categories by industry
and discipline, the Thermosense symposia usually devote at least one session to
each of the following categories:

1. Plant Condition Monitoring and Predictive Maintenance

2. Buildings and Infrastructure
3. Materials Evaluation – Infrared Nondestructive Testing
4. Process Monitoring and Control
5. Night Vision, Security, and Surveillance
6. Life Sciences Thermography
7. Research and Development (R&D)

The first six classifications are self-explanatory; the seventh is a catch-all to include
the introduction of new instrumentation or experimental techniques. Papers on sub-
jects classified as “R&D” one year will often be included in one of the other classi-
fications in subsequent years as the instrumentation or techniques mature.
Although these classifications have evolved somewhat over the years, they repre-
sent reasonable subdivisions. Therefore, the chapters in Part II are organized in
general accordance with these classifications.
To assist the user in instrument selection, Appendix A contains a tabulation of
currently available instruments by category and manufacturer, including a digest of
performance characteristics and features. Appendix B is a current index of manu-
facturers’ websites, addresses, and phone numbers.
The text also includes quick reference charts and tables to aid the user in on-site
measurements (Appendix C) and a glossary of IR/thermography terms (Appendix D).
Preface xxiii

I would like to acknowledge the contributions of the following organizations

for providing data and background for this text:

American Risk Consultants Corp.

Bales Scientific
General Motors Powertrain
Goodyear Corp. Barnes Engineering Div.
Electric Power Research Institute
Electrophysics, Inc.
FLIR Systems, Inc.
Fluke Thermography
Infrared Thermal Imaging, Inc.
ISI Group, division of Mine Safety Appliances
Honeywell Corp.
Linear Laboratories, Safetytek Corp.
Magnavox Electro-optical Systems
Meditherm
Mikron Infrared
Mine Safety Appliances Corp.
Quantum Focus Instruments
Raytek, Inc., a Fluke company
Raytheon Corp.
SI Termografia Infrarroja
Thermal Wave Imaging, Inc.
Toledo Edison
Waterfall Solutions

I would like to express my thanks to Rob Spring, P.E., of Snell Infrared, for his dedi-
cation to training in our technology, and for applying his instructor’s eye to the ex-
pert review of this third edition.
I would also like to express my thanks to Paul Zayicek of Electric Power Re-
search Institute’s NDE Center for his professionalism, his vigorous promotion of
IR thermography, his many contributions to the body of knowledge in thermo-
graphy, and for reviewing the second edition of this text (1999).
Finally, I would like to express my appreciation to Ron Lucier of FLIR Systems
Inc. for his careful and conscientious review of the first edition of this text (1993),
and for his many contributions to the first and subsequent editions.

Herbert Kaplan
Boynton Beach, Florida
January 2007
 Part I

Basics and Instrument

Overview
Chapter 1

Introduction

1.1 Overview of This Text

This tutorial text will familiarize the reader with the operating principles and practi-
cal performance characteristics of commercial infrared (IR) thermal sensing and
imaging instruments, and will guide the reader in their selection and application.
The early chapters (Part I) include a brief review of the principles of heat flow, a
review of the basic principles of IR radiometry and thermography, and a discussion
of how these principles are reflected in instrument design and performance. Later
chapters (Part II) illustrate how these performance parameters are utilized to solve a
wide variety of applications problems.

1.2 Reasons for Using IR Instruments

The temperature and thermal behavior of plant machinery, power generation and
distribution equipment, materials, and fabricated parts in process are the most criti-
cal factors in the manufacturing process and in the maintenance of safe and
cost-effective plant operations. For this reason, operating temperature is frequently
considered the key to successful plant maintenance and is, by far, the most mea-
sured quantity in industrial process monitoring and control. The flow of thermal en-
ergy through structures is a fair indication of their structural integrity and insulating
properties. Therefore, thermal measurements are used in studying the properties of
materials and in energy conservation programs.
As the result of improvements in performance, precision, packaging, and
software, these instruments are finding new applications every day in areas as di-
verse as law enforcement, biological threat detection, machine vision, and fire-
fighting.
Modern IR sensing and imaging instruments are light in weight, easy to use,
and rugged compared to similar instruments of just a few years ago. Their steadily
increasing use in the workplace, despite their cost, is easily justified in terms of
their many advantages. However, for the most part they are still more complex and
costly than conventional contacting instruments.
Although conventional methods of temperature measurement using thermome-
ters and thermocouples are still commonly used for many applications, IR sensors
have become less expensive, more reliable, and electrically interchangeable with
conventional thermistors and thermocouples. For this reason, noncontact measure-

3
4 Chapter 1

ment using IR sensors has become an increasingly desirable alternative to conven-

tional methods. With the introduction of innovative computer hardware and
software, computer-aided predictive maintenance and full image thermal control of
products and processes is now possible.

1.3 Advantages of Noncontact Thermal Measurement

The four most commonly stated advantages of noncontact thermal IR measurement
over contact measurement are that it is nonintrusive, remote, much faster than con-
ventional methods, and that it measures the temperature (or radiant thermal distri-
bution) at the surface of the object of interest (we will call it the target), not the
surrounding air. Any one, or a combination of, the following conditions warrant the
consideration of a noncontact IR sensor:

· Target in motion—When the target to be measured is moving, it is usually im-

practical to have a temperature sensor in contact with its surface. Bouncing,
rolling, or friction can cause measurement errors, and the sensor may interfere
with the process.
· Target electrically “hot”—Current-conducting equipment and components
present a hazard to personnel and instruments alike. Infrared sensors place both
out of harm’s way.
· Target fragile—When thin webs or delicate materials are measured, a contact-
ing sensor can often damage the product.
· Target very small—The mass of a contacting sensor that is large with respect
to the target being measured will usually conduct thermal energy away from the
target surface, reduce the temperature, and produce erroneous results.
· Target remote—If a target is very far away from, or inaccessible to, contacting
sensors, IR measurement is the only option.
· Target temperature changing—Infrared sensors are much faster than
thermocouples. Infrared radiant energy travels from the target to the sensor at
the speed of light, and a rapidly changing temperature can be monitored with
millisecond response, or faster, by IR sensors.
· Target destructive to thermocouples—When the high mortality rate of
thermocouples due to jarring, burning, or erosion becomes a serious factor, an
IR sensor is a far more cost-effective alternative.
· Multiple measurements required—When many points on a target need to be
measured, it is usually more practical to re-aim an IR sensor than to reposition a
thermocouple, or to deploy a great number of thermocouples. The fast response
of the IR sensor is also important here.

When IR scanning and imaging systems are applied to solve temperature moni-
toring and control problems, another very powerful advantage is apparent: the
ability to scan many points on the product surface in an extremely short time and
produce thermal maps for visual inspection or automatic computer-controlled
Introduction 5

analysis. Thermal maps are called thermograms. The thermogram of a target

may be presented in terms of surface radiant energy contrast, in which case it is
called a qualitative thermogram. It is more often presented in terms of apparent
surface temperature distribution, in which case it is called a quantitative ther-
mogram.
There are, of course, limitations to the noncontact approach—conditions that
may make it impractical or ineffective. These will become apparent as the discus-
sions progress.

1.4 Some Historical Background

When materials get very hot (above 100°C), they radiate energy in the visible as
well as in the IR, and the color of a glowing metal is a fair indication of its tempera-
ture (the whiter the color, the higher the temperature). The ancient sword maker and
blacksmith knew from the color of a heated metal when it was time to quench and
temper. This technique is still in use today; precision optical “matching” pyrome-
ters are used to match the “brightness color” of a product with that of a glowing fila-
ment, and the brightness of the filament is controlled by adjusting a knob calibrated
in temperature. The next logical step is to substitute a photomultiplier for the opera-
tor’s eye and thus calibrate the measurement. Finally, a differential measurement is
made between the actual brightness of the product and the desired brightness (the
set point), and the differential signal is injected into the process and used to drive
the product temperature to the set point.
With the advent of modern IR detectors, the precision measurement of thermal
energy radiating from surfaces that do not “glow” visibly became possible. Mea-
surements of cool surfaces, well below 0°C, are routinely accomplished with even
the least expensive of IR sensors.
The formal discovery of IR energy beyond the visible light portion of the spec-
trum is credited to William Herschel (1738–1822). Herschel was a musician who
studied science, optics, and astronomy as avocations; they eventually became his
life’s work. Around the year 1800, he set up an experiment to learn if the variously
colored rays from a beam of sunlight dispersed by a prism might differ in their
power to heat a surface. His experiment included a prism, a pasteboard, and three
thermometers, which were then relatively new scientific instruments. After placing
the thermometers under the red, green, and violet lights, he devised “heating ef-
fects” roughly proportional to 55 for red, 24 for green, and 16 for violet. (There is
no reference to the units of measurement.) Suspecting that the heating effect might
continue to increase beyond the red, Herschel repeated his experiment using ruled
paper and found that the maximum heating occurred some distance beyond the red
light (about 1/2 inch). No heating was detected at the other end beyond the violet.
Herschel went on to establish that radiant heat, like light, can refract through
materials and reflect off surfaces. It is interesting to note that all of these observa-
tions were made at a time when both light and radiant heat were thought to consist
of material particles.
6 Chapter 1

1.5 Evolution of IR Cameras

Although conceptualized in much earlier writings, practical IR scanning and imag-
ing instruments were not built until military requirements for night vision tools
stimulated the development of IR line scanners in the late 1940s and IR thermal
viewers in the early 1950s. The first real-time (15 frames per second) field-de-
ployable passive IR units (the U.S. Army’s AN/PAS series) using thermoelectrical-
ly (TE)-cooled lead selenide (PbSe) linear arrays with mirror scanners were
field-tested in the 1960s and deployed in the 1970s. The first commercial units
(AGA 110) based on the AN/PAS were produced in 1983 and featured a TE-
cooled, 48-element PbSe linear array (2–5 µm) and an oscillating mirror scanner.
The AGA 110 weighed about 20 lbs including a battery belt. These produced quali-
tative thermograms and were used for plant predictive maintenance, roof scans, and
materials testing, as well as security and surveillance.
The first real-time thermal imager that produced quantitative thermograms was
introduced in 1963 (AGA Thermovision). These imagers used liquid nitrogen-
cooled indium antimonide (InSb) as a detector and two high-speed scanning optical
elements to produce the image. It weighed more than 70 lbs. Over the next several
years, advancing technology resulted in improved performance, compact designs,
and a reduced price of quantitative thermal imagers, as well as the introduction of
computer-based diagnostic software.
Airborne forward-looking infrared (FLIR) systems using cryogenically cooled,
InSb (3–5 µm) linear focal plane arrays were available as early as the 1960s. The ar-
rays were oriented normal to the aircraft’s flight and used this “push broom” scan-
ning approach to produce aerial IR maps. They were massive and costly.
Infrared focal plane array (IRFPA) imagers based on 2D “staring” arrays were
perfected in the late 1980s. Mitsubishi introduced the first commercial FPA ther-
mal imager (Model 5120C) using a Stirling-cycle-cooled platinum silicide (PtSi)
array (2–5 µm) in 1989. (The Stirling-cycle cooler is a compact, sealed, elec-
tric-powered gas refrigeration unit into which the detector array is integrated. It is
currently the cooler most commonly used in commercial IR cameras where cool-
ing is required.)
The use of the “staring” array eliminated the need for scanning optics and all of
the dynamics and complexity they entail. Detector cooling, however, was still re-
quired, and the temperature measuring capability was not yet available.
The 1990s saw the most rapid advances in FPA technology and a wide prolifer-
ation of new cameras. In the early 1990s, compact, hand-held, radiometric FPA
cameras became available, producing computer-compatible quantitative thermo-
grams, on-board processing software, and a choice of Stirling-cycle-cooled detec-
tors, such as InSb (3–5 µm), mercury cadmium telluride (HgCdTe) (8–12 µm), and
gallium arsenide (GaAs) quantum well IR photodetectors (QWIPs) in selected
bands from 4–10 µm.
Uncooled long-wave IRFPA cameras were developed in the mid-1990s. These
featured uncooled microbolometric and ferroelectric detector arrays (8–14 µm),
Introduction 7

and required no detector cooling and no scanning. Solid state thermoelectric de-
vices are used only to temperature-stabilize uncooled detector arrays.
At this writing, full-featured IR cameras are commonly available that weigh
less than 1 lb., are about the size of a hair blower, and are priced at less than $7000,
with prices expected to drop even farther over the next few years.
Chapter 2

Basics of Noncontact Thermal

Measurements

2.1 Heat Transfer and Radiation Exchange Basics

This section will provide the reader with an understanding of how heat transfer
phenomena affect noncontact IR thermal sensing and thermographic measure-
ments. Since making IR measurements depends on measuring the distribution of
radiant thermal energy (heat) emitted from a target surface, the thermographer
must have a sound understanding of heat, temperature and the various types of
heat transfer to undertake an effective program of IR thermal imaging, or
thermography.

2.1.1 Heat and temperature

What we often refer to as a heat source (like an oil furnace or an electric heater) is
really one form or another of energy conversion; the energy stored in one object is
converted to heat and flows to another object. Heat can be defined as thermal en-
ergy in transition. It flows from one place or object to another as a result of temper-
ature difference, and the flow of heat changes the energy levels in the objects.
Temperature is a property of matter and not a measurement of internal energy. It de-
fines the direction of heat flow when another temperature is known.

Heat always flows from the object that is at the higher temperature to the object that
is at the lower temperature.

As a result of heat transfer, hotter objects tend to become cooler and cooler ob-
jects become hotter, approaching thermal equilibrium. To maintain a steady-state
condition, energy needs to be continuously supplied to the hotter object by some
means of energy conversion so that the temperatures, and hence the heat flow, re-
main constant.

2.1.2 Converting temperature units

Temperature is expressed in either absolute or relative terms. There are two abso-
lute scales called Rankine (English system) and Kelvin (metric system). There are

9
10 Chapter 2

two corresponding relative scales called Fahrenheit (English system) and Celsius
or centigrade (metric system).
Absolute zero is the temperature at which no molecular action takes place. This
is expressed as zero Kelvins or zero Rankines (0 K or 0 R). Relative temperature is
expressed as degrees Celsius or degrees Fahrenheit (°C or °F). The numerical rela-
tions among the four scales are as follows:

TFahrenheit – 32
TCelsius = , (2.1)
1.8
TFahrenheit = 1.8 (TCelsius + 32), (2.2)
TRankine = TFahrenheit + 459.69, (2.3)
TKelvin = TCelsius + 273.16. (2.4)

Absolute zero is equal to –273.1°C and to –459.7°F. To convert changes in temper-

ature or delta T (DT) between the English and metric systems, the simple 9/5 (1.8
to 1) relationship is used:

A DT of 1°Celsius is equal to a DT of 1.8°Fahrenheit. (2.5)

Table 2.1, located at the end of this chapter, is a conversion table to allow the rapid
conversion of temperature between Fahrenheit and Celsius values. The table in-
cludes instructions for its use.

2.1.3 Three modes of heat transfer

There are three modes of heat transfer: conduction, convection, and radiation. All
heat transfer processes occur by one or more of these three modes. Infrared thermo-
graphy is based on the measurement of radiative heat flow and is therefore most
closely related to the radiation mode of heat transfer.

2.1.4 Conduction
Conduction is the transfer of heat in stationary media. It is the only mode of heat
flow in solids but can also take place in liquids and gases. It occurs as the result of
molecular collisions (in liquids) and atomic vibrations (in solids) whereby energy is
moved, one molecule at a time, from higher temperature sites to lower temperature
sites. Figure 2.1 is an illustration of conductive heat flow.
The Fourier conduction law expresses the conductive heat flow through the
slab shown in Fig. 2.1,

Q k(T1 – T2)
= , (2.6)
A L
Basics of Noncontact Thermal Measurements 11

Figure 2.1 Conductive heat flow.

where Q/A is the rate of heat transfer through the slab per unit area (BTU/h-ft2)
perpendicular to the flow, L is the thickness of the slab (ft), T1 (deg F) is the
higher temperature (at the left), T2 is the lower temperature (at the right), and k is
the thermal conductivity of the slab material. Thermal conductivity is analogous
to electrical conductivity and inversely proportional to thermal resistance, as
shown in the lower portion of Fig. 2.1. The temperatures T1 and T2 are analogous
to voltages V1 and V2, and the heat flow Q/A is analogous to electrical current I,
so that if

V1 – V2
R electrical = , (2.7)
I

then

T1 – T2 L
R thermal = = . (2.8)
Q A k

Heat flow is usually expressed in English units, where k is expressed in

BTU/hr-ft2-°F and thermal resistance is in °F-hr-ft2/BTU.

2.1.5 Convection
Convective heat transfer takes place in a moving medium and is almost always as-
sociated with transfer between a solid and a moving fluid (such as air). Forced con-
vection takes place when an external driving force, such as a wind or an air pump,
moves the fluid. Free convection takes place when the temperature differences nec-
essary for heat transfer produce density changes in the fluid and the warmer fluid
rises as a result of increased buoyancy.
12 Chapter 2

Figure 2.2 Convective heat flow.

In convective heat flow, heat transfer takes effect by means of two mechanisms; the
direct conduction through the fluid, and the motion of the fluid itself. Figure 2.2 illus-
trates convective heat transfer between a flat plate and a moving fluid.
The presence of the plate causes the velocity of the fluid to decrease to zero at
the surface and influences its velocity throughout the thickness of a boundary layer.
The thickness of the boundary layer depends on the free velocity, V, of the fluid. It is
greater for free convection and smaller for forced convection. The rate of heat flow
depends in turn on the thickness of the convection layer as well as the temperature
difference between Ts and T¥ (Ts is the surface temperature, T¥ is the free field fluid
temperature outside the boundary layer). Newton’s cooling law defines the convec-
tive heat transfer coefficient as

Q A
h= , (2.9)
Ts – T¥

where h is expressed in BTU/hr-ft2-°F.

By rearranging Eq. (2.9), we obtain

Q T
= Ts – , (2.10)
A Rc

where Rc =1/h is the resistance to convective heat flow. Rc is also analogous to elec-
trical resistance and is easier to use when determining combined conductive and
convective heat transfer.

2.1.6 Radiation
Radiative heat transfer is unlike the other two modes in several respects:

1. It can take place across a vacuum.

2. It occurs by electromagnetic emission and absorption.
3. It occurs at the speed of light.
4. The energy transferred is proportional to the fourth power of the temperature
difference between the objects.
Basics of Noncontact Thermal Measurements 13

Figure 2.3 Infrared in the electromagnetic spectrum.

The electromagnetic spectrum is illustrated in Fig. 2.3. Radiative heat transfer takes
place in the IR portion of the spectrum, from 0.75 µm to about 100 µm, although
most practical measurements can be made out to about 20 µm (µ or µm stands for
micrometers or microns. A micron is one-millionth of a meter and the measurement
unit for radiant energy wavelength).

2.1.7 Radiation exchange at the target surface

The measurement of thermal IR radiation is the basis for noncontact temperature
measurement and thermography. Thermal IR radiation leaving a surface (W) is
called exitance or radiosity. It can be emitted from the surface, reflected off the sur-
face, or transmitted through the surface. This is illustrated in Fig. 2.4. The total
radiosity is equal to the sum of the emitted component (We), the reflected compo-
nent (Wr) and the transmitted component (Wt). The surface temperature is related
to We, the emitted component, only.

Figure 2.4 Radiative heat flow.

14 Chapter 2

Figure 2.5 Radiation impinging on a surface.

Thermal IR radiation impinging on a surface can be absorbed, reflected, or trans-

mitted as illustrated in Fig. 2.5. Kirchhoff’s law states that the sum of the three com-
ponents is always equal to the received radiation (the percentage sum of the three
components equals unity):

a (absorptivity) + r (reflectivity) + t (transmissivity) = 1.

2.1.8 Specular and diffuse surfaces

The roughness and surface characteristics will determine the type and direction of re-
flection of incident radiation. A smooth surface will reflect incident energy at an an-
gle complementary to the angle of incidence. This is called a specular reflector.
A rough or structured surface will scatter or disperse some of the incident radiation.
This is called a diffuse reflector. No perfectly specular or perfectly diffuse surface can
exist in nature. All real surfaces have some diffusivity and some specularity.
When making practical measurements, the specular or diffusing characteristics
of a target surface are taken into effect by accounting for the emissivity of the sur-
face. Emissivity is discussed as part of the detailed discussion of the characteristics
of IR thermal radiation in Sec. 2.3.

2.1.9 Transient heat exchange

The discussions of three types of heat exchange in Secs. 2.1.4–2.1.6 deal with
steady-state heat exchange for reasons of simplicity and ease of understanding.
Two fixed temperatures are assumed to exist at the two points between which the
heat flows. In many applications, however, temperatures are in transition, so that
the values shown for energy radiated from a target surface are the instantaneous
Basics of Noncontact Thermal Measurements 15

values at the moment measurements are made. There are numerous instances where
existing transient thermal conditions are exploited in order to use thermography to
reveal material or structural characteristics in test articles. The thermogram of the
outside surface of an insulated vessel carrying heated liquid, for example, should be
relatively isothermal and somewhat warmer than the ambient air. Insulation voids
or defects will cause warm anomalies to appear on the thermogram, allowing the
thermographer to pinpoint areas of defective or damaged insulation. Here a passive
approach can be taken because the transient heat flow from the liquid through the
insulation to the outside air produces a characteristic thermal pattern on the product
surface. Similarly, water-saturated areas on flat roofs will retain solar heat well into
the night. Long after the dry sections have radiated their stored heat to the cold night
sky, the saturated sections will continue to radiate, and will appear as warm anoma-
lies to the thermographer.
When there is no heat flow through the material or the test article to be evalu-
ated, an active, or thermal injection, approach is used to generate a transient heat
flow. This approach requires: (1) the generation of a controlled flow of thermal en-
ergy across the laminar structure of the sample material under test; (2) thermo-
graphic monitoring of one of the surfaces (or sometimes both) of the sample; and
(3) the search for the anomalies in the thermal patterns so produced that will indi-
cate a “defect” in accordance with established accept-reject criteria. This approach
has been used extensively and successfully by the aerospace community in the
evaluation of composite structures for impurities, flaws, voids, disbonds, delamina-
tions, and variations in structural integrity. A more detailed discussion of thermal
IR nondestructive material testing is provided in Chapter 9.

2.2 Infrared Measurement Problem

All targets radiate energy in the IR spectrum, as shown in Fig. 2.7. The hotter the
target, the more energy is radiated. Very hot targets radiate in the visible as well, and
our eyes can see this because they are sensitive to light. For example, the sun at
about 6000 K appears to glow almost white hot, a tungsten filament at about 3000 K
has a yellowish glow, and an electric stove element at 800 K glows red. As the stove
element cools it loses its visible glow but it continues to radiate. We can feel it with
a hand placed near the surface but we can’t see the glow because the energy has
shifted from red to IR. Infrared detectors can sense IR radiant energy and produce
useful electrical signals proportional to the temperature of target surfaces. Instru-
ments using IR detectors and optics to gather and focus energy from the targets onto
these detectors are capable of measuring target surface spot temperatures with sen-
sitivities down to 0.1°C and with response times in the microsecond range. They
are called point sensors or spot radiometers. Instruments that combine this mea-
surement capability with mechanisms for scanning the target surface are called in-
frared thermal imagers or infrared cameras. They can produce thermal maps or
thermograms where the brightness intensity or color hue of any spot on the map is
representative of the temperature of the surface at that point.
16 Chapter 2

In most cases, thermal imagers can be considered as extensions of radiation

thermometers or as arrays of radiation thermometers operating simultaneously. The
performance parameters of thermal imagers are extensions of the performance pa-
rameters of radiation thermometers. For ease of understanding, therefore, the basic
measurement problem is discussed in this chapter in terms of the measurement of a
single point. It is then expanded to cover thermal scanning and imaging.

2.2.1 Noncontact thermal measurements

Infrared noncontact thermal sensors are classified as infrared radiation thermometers
by the American Society for Test and Measurement (ASTM) even though they don’t
always read out in temperature. The laws of physics allow us to convert IR radiation
measurements to temperature measurements. We do this by measuring the self-emitted
radiation in the IR portion of the electromagnetic spectrum from target surfaces and
converting these measurements to electrical signals. In making these measurements
three sets of characteristics need to be considered, as illustrated in Fig. 2.6:

· The target surface.

· The transmitting medium between the target and the instrument.
· The measuring instrument.

2.2.2 Target surface

The chart of the electromagnetic spectrum (Fig. 2.3) indicates that the IR portion of
the spectrum lies adjacent to the visible. Every target surface above absolute zero
(0 K or –273°C) radiates energy in the IR. The hotter the target, the more radiant en-
ergy is emitted. When targets are hot enough they radiate or “glow” in the visible part
of the spectrum as well. As they cool, our eyes become incapable of seeing their emit-
ted radiation and they appear not to glow at all. Infrared sensors are employed here to
measure the radiation in the IR, which is related to target surface temperature.
The visible spectrum extends from energy wavelengths of 0.4 µm for violet
light to about 0.75 µm for red light. The IR spectrum extends from 0.75 µm to about
20 µm for practical purposes of temperature measurement.
Figure 2.7 shows the distribution of emitted energy over the electromagnetic
spectrum of targets at various temperatures. The sun, at 6000 K, appears almost
white hot since its emitted energy is centered over the visible spectrum with a peak
at 0.5 µm. Other targets, such as a tungsten filament at 3000 K, a red hot surface at
800 K, and the ambient earth at 300 K (about 30°C) are also shown in this illustra-
tion. It becomes apparent that, as surfaces cool, not only do they emit less energy,
but the wavelength distribution shifts to longer IR wavelengths. Even though the
eye becomes incapable of sensing this energy, IR sensors can “see” these invisible
longer wavelengths. They enable us to measure the self-emitted radiant energy
from even very cold targets and, thereby, determine the temperatures of target sur-
faces remotely and without contact.
Basics of Noncontact Thermal Measurements 17

Figure 2.6 Three sets of characteristics in making IR measurements.

Figure 2.7 Blackbody curves at various temperatures.

18 Chapter 2

Two physical laws define the radiant behavior illustrated in Fig. 2.7:

The Stephan-Boltzmann law,

W = deT4, (2.11)

and Wien’s displacement law,

b
lm = , (2.12)
T

where W = radiant flux emitted per unit area (watts/cm2),

e = emissivity (unity for a blackbody target),
d = Stephan-Boltzmann constant = 5.673 ´ 10 12 watts cm 2 K 2,
T = absolute temperature of target (K),
lm = wavelength of maximum radiation (µm), and
b = Wien’s displacement constant = 2897 (µm-K).

According to Eq. (2.11), the radiant energy emitted from the target surface (W)
equals two factors multiplied by the fourth power of the absolute temperature (T) of
the target. The instrument measures W and calculates T. One of the two factors (d)
is a constant (fixed number). Emissivity (e) is the other factor, and is a surface charac-
teristic that is constant for a specific material over a given range of temperatures and
under specific measurement conditions. For point measurements we can usually esti-
mate the emissivity setting we need to dial into the instrument from available tables
and charts. We can also learn experimentally the proper setting needed to make the
instrument produce the correct temperature reading by using samples of the actual
target material. We call this more practical setting value effective emissivity (e*).
According to Eq. (2.12), the wavelength at which a target radiates its peak en-
ergy is defined as simply a constant (b = 2897 » 3000) divided by the target temper-
ature (T) in Kelvins. For the 300 K ambient earth, for example, the peak wavelength
would be » 3000/300 or » 10 µm. This quick calculation is important in selecting
the proper instrument for a measurement task, as will be discussed in Chapter 3.
Target surfaces can be classified in three categories: blackbodies, graybodies,
and non-graybodies. The targets shown in Fig. 2.7 are all blackbody radiators (or
blackbodies). A blackbody radiator is a theoretical surface having unity emissivity at
all wavelengths and absorbing all of the energy available at its surface. This would be
an ideal target to measure since the temperature calculation within the instrument
would be simply mechanized and always constant. Fortunately, though blackbody ra-
diators do not exist in practice, the surface of most solids are graybodies, that is, sur-
faces whose emissivities are high and fairly constant with wavelength.
Figure 2.8 shows the comparative spectral distribution of energy emitted by a
blackbody, a graybody and a non-graybody, all at the same temperature. For gray-
body measurements a simple emissivity correction can usually be implemented
Basics of Noncontact Thermal Measurements 19

Figure 2.8 Spectral distributions of a blackbody, graybody, and non-graybody.

when temperature measurements are required. For non-graybodies the solutions are
a bit more difficult. To understand the reason for this, we must see what an instru-
ment sees when it is aimed at a non-gray target surface.
Figure 2.9 shows that the instrument sees three components of energy: emitted
energy (We), reflected energy from the environment (Wr) and, energy transmitted
through the target from sources behind the target (Wt). The percentage sum of these
components is always unity.
If the emissivity (e) of a graybody is very low, as in the case of polished metal
surfaces, the reflectance (r) becomes high (r = 1 – e) and can generate erroneous
readings if not properly handled. Reflected energy from a specific source can gen-
erally be redirected by proper orientation of the instrument with respect to the target
surface, as shown in Fig. 2.10. This illustrates the proper and improper orientation
for avoiding reflected energy from a specific source.

Figure 2.9 Components of energy reaching the measuring instrument.

20 Chapter 2

Figure 2.10 Aiming the instrument to avoid point reflections.

Since a blackbody reflects and transmits nothing, the instrument sees only We, the
emitted energy, when aimed at a blackbody target. For a graybody, the instrument
sees We and Wr, the emitted and reflected energy. Since a non-graybody may be
partially transparent, the instrument sees all three components when aimed at a
non-graybody. Often, in practice, the troublesome component is Wt, the energy
transmitted through a non-gray target from sources behind the target. A discussion
of solutions to this type of problem is included in Chapter 3.

2.2.3 Transmitting medium

The transmission characteristics of the medium in the measurement path between
the target and the instrument need to be considered in making noncontact thermal
measurements. No loss of energy is encountered when measuring through a vac-
uum. Furthermore, for short path lengths (a few feet, for example), most gases, in-
cluding the atmosphere, absorb very little energy and can be ignored (except where
measurements of precision temperature values are required). As the path length in-
creases, or as the air becomes heavy with water vapor, the energy loss by atmo-
spheric absorption may become significant. It is then necessary to consider the IR
transmission characteristics of the atmosphere.
Figure 2.11 illustrates the spectral transmission characteristics of 10 meters of
ground level atmosphere. Two spectral intervals can be seen to have very high
transmission. These are known as the 1–5 µm and the 8–14 µm atmospheric win-
dows, and almost all IR sensing and scanning instruments are designed to operate in
one or the other of these windows. Usually, the difficulties encountered with trans-
mitting media occur when the target is viewed by the instrument through another
solid object such as a glass or quartz viewing port. Figure 2.12 shows transmission
curves for various samples of glass and quartz. Upon seeing these, our first impres-
sion is that glass is opaque at 10 µm where ambient (30°C) surfaces radiate their
peak energy. This impression is correct and although in theory IR measurements
can be made of 30°C targets through glass, it is hardly practical. The first approach
to the problem is to attempt to eliminate the glass, or at least a portion through
Basics of Noncontact Thermal Measurements 21

Figure 2.11 Infrared atmospheric transmission for a 10-meter path at sea level (50%
relative humidity).

Figure 2.12 Spectral characteristics of glass samples (percent transmission, absorp-

tion, and reflectance).

which the instrument can be aimed at the target. If, for reasons of hazard, vacuum,
or product safety, a window must be present, we might substitute a material that
transmits in the longer wavelengths. Figure 2.13 shows the spectral transmission
characteristics of several of these materials, many of which transmit energy past
10 µm. A more detailed discussion of IR transmitting windows for inspection of
mid- and high-voltage electrical equipment is provided in Sec. 5.3.8. These materi-
als are often used as lenses and optical elements in low temperature IR sensors. Of
course, as targets become hotter, and the emitted energy shifts to the shorter wave-
lengths, glass and quartz windows pose less of a problem and are even used as ele-
ments and lenses in high temperature sensing instruments.
The characteristics of the window material will always have some effect on the
temperature measurement, but the attenuation can always be corrected by preca-
22 Chapter 2

Figure 2.13 Transmission of IR transmitting materials.

librating the instrument with a sample window placed between the instrument and a
target of known temperature.
In closing the discussion of the transmitting medium, it is important to note that
IR sensors can only work properly when all of the following spectral ranges coin-
cide or overlap:

· The spectral range over which the target emits.

· The spectral range over which the media transmits.
· The spectral range over which the sensor (the instrument) operates.

2.2.4 Measuring instrument

Figure 2.14 shows the necessary components of an IR radiation thermometer. Col-
lecting optics (an IR lens, for example) are necessary in order to focus the energy
emitted by the target onto the sensitive surface of an IR detector, which in turn con-
verts this energy into an electrical signal.
Basics of Noncontact Thermal Measurements 23

Figure 2.14 Components of an IR radiation thermometer.

When an IR radiation thermometer (point sensing instrument) is aimed at a target, it

collects energy within a collecting beam, the shape of which is determined by the
configuration of the optics and the detector. The cross section of this collecting
beam is called the field of view (FOV) of the instrument and it determines the size of
the area (spot size) on the target surface that is measured by the instrument. On
scanning and imaging instruments this is called the instantaneous field of view
(IFOV) and becomes one picture element on the thermogram.
Infrared optics are available in two general configurations, refractive and re-
flective. Refractive optics (lenses), which are at least partly transparent to the wave-
lengths of interest, are used most often for higher-temperature applications, where
their throughput losses can be ignored. Reflective optics (mirrors), which are more
efficient but somewhat complicate the optical path, are used more often for
low-temperature applications, where the energy levels cannot warrant throughput
energy losses. An IR interference filter is often placed in front of the detector to
limit the spectral region or band of the energy reaching the detector. The reasons for
spectral selectivity will be discussed later in this section.
The processing electronics unit amplifies and conditions the signal from the IR
detector and introduces corrections for such factors as detector ambient tempera-
ture drift and target surface emissivity. Generally, a meter indicates the target tem-
perature, and an analog and/or digital output is provided. The digital/analog signal
is used to record, display, alarm, control, correct, or any combination of these tasks.
Figure 2.15 illustrates the configuration of a typical instrument employing all
of the elements we have discussed. The germanium lens collects the energy from a
spot on the target surface and focuses it on the surface of the radiation thermopile
detector. The 8–14 µm filter limits the spectral band of the energy reaching the de-
tector so that it falls within the atmospheric window. The detector generates a direct
current electromagnetic force (dc emf) proportional to the energy emitted by the
target surface. The auto-zero amplifier senses ambient temperature changes and
prevents ambient drift errors. The output electronics unit conditions the signal and
computes the apparent target surface temperature based on a manual emissivity set-
24 Chapter 2

Figure 2.15 Typical IR radiation thermometer schematic (courtesy of Linear Labora-

tories).

ting. The analog output terminals accept a 15–30 volts DC (VDC) loop supply and
generate a 4–20 mA signal proportional to target surface temperature.
All IR detector-transducers exhibit some electrical change in response to the
radiant energy impinging on their sensitive surfaces. Depending on the type of de-
tector this may be an impedance change, a capacitance change, the generation of
an emf (voltage), or the release of photons. Detectors are available with response
times as fast as nanoseconds or as slow as fractions of seconds. Depending on the
requirement, either a broadband detector or a spectrally limited detector can be
selected.
Infrared detectors fall into two broad categories; thermal detectors that have
broad, uniform spectral responses, somewhat lower sensitivities and slower re-
sponse times (on the order of milliseconds), and photodetectors (also called photon
detectors) that have limited spectral responses, higher peak sensitivities and faster
response times (on the order of microseconds). Thermal detectors will generally
operate at or near room temperature, while photodetectors are generally cooled to
optimize performance. The HgCdTe detector, for example, is a photodetector
cooled to 77 K for 8–14 µm operation and to 195 K for 3–5 µm operation. Because
of its fast response, this detector is used extensively in high-speed scanning and im-
aging applications. The radiation thermopile, on the other hand, is a broad-band
thermal detector operating uncooled. It is used extensively for spot measurements
of relatively cool targets. Since it generates a dc emf proportional to the radiant en-
ergy reaching its surface, it is ideal for use in portable, battery-powered instru-
ments. Figure 2.16 illustrates the spectral responses of various IR detectors.
The applicability for these detectors to specific imaging applications is dis-
cussed in greater detail in later chapters.
Point-sensing instruments for measuring very hot targets usually operate in
shorter wavelengths, 0.9–1.1 µm, for example. This is known as the near infrared
(NIR) [or sometimes the short-wave infrared (SWIR) region]. Instruments for mea-
suring cooler targets usually operate in longer wavelengths (2–5 µm or 8–14 µm,
Basics of Noncontact Thermal Measurements 25

Figure 2.16 Response curves of various IR detectors.

for example). Most IR thermal imagers operate in either the 2–5 µm, known as the
mid-wave infrared (MWIR) region or 8–12 µm spectral region, known as the
long-range infrared (LWIR) region.

2.3 Thermal Scanning and Imaging Instruments

When problems in temperature monitoring and control cannot be solved by the
measurement of one or several discrete points on a target surface it becomes neces-
sary to spatially scan, that is to move the collecting beam (FOV) of the instrument
relative to the target. In the past this was done by inserting a movable optical ele-
ment into the collecting beam as illustrated in Fig. 2.17(a). Since the advent of
IRFPA detectors, line scanning instruments have become available with multi-ele-
ment linear arrays as illustrated in Fig. 2.17(b). A brief overview discussion of
scanning and imaging instruments follows.

2.3.1 Line scanning

The purpose of spatial scanning is to derive information concerning the distribution
of radiant energy over a target scene. Quite often a single straight line scanned on
the target is all that is necessary to locate a critical thermal anomaly. This can be ac-
complished by a single detector element and a scanning mirror or, most recently, by
a linear FPA where the location of each detector element in the linear array estab-
lishes the radiometric output signal for each point on the scan line.
26 Chapter 2

Figure 2.17 (a) The addition of a scanning element to a radiation thermometer for
single line scanning. (b) Eliminating the scanning element – the substitution of a lin-
ear FPA detector for the single element detector.

A typical high-speed commercial line scanner develops a high-resolution thermal

map by orienting the linear detector array normal to the motion of a moving target
such as a paper web or a strip steel process. The resulting output is a thermal strip
map of the process as it moves normal to the scan line. The scanning configuration
is illustrated in Fig. 2.18. The output signal information is in real-time computer
compatible format and can be used to monitor, control or predict the behavior of the
target.

2.3.2 Two-dimensional opto-mechanical scanning

To add another dimension to the scanning capability of an opto-mechanically
scanned instrument generally calls for an additional scanning element. Opto-me-
chanically scanned instruments have, for the most part, been superceded by instru-
ments using two-dimensional IR focal plane staring arrays, although there are still
opto-mechanically scanned imagers in use. For reference purposes, the schematic
of Fig. 2.19 illustrates the configuration of a typical raster scanning IR radiometer.
Basics of Noncontact Thermal Measurements 27

Figure 2.18 Infrared line scanner schematic and scanner operation.

Figure 2.19 Infrared opto-mechanical scanning imager (courtesy of FLIR Systems, Inc.).

2.3.3 Infrared focal plane array (IRFPA) cameras

In the mid 1980s detector mosaics or staring IRFPAs were used successfully for
military night vision FLIR viewers and, in the 1990s, were widely available for use
in commercial thermal imaging instruments. As of this writing, all commercially
marketed IR cameras incorporate staring focal plane detector arrays. In an IRFPA
camera each detector element is assigned one display picture element and mechani-
28 Chapter 2

cal scanning is eliminated altogether. IRFPA radiometers are adaptations of mili-

tary and aerospace FLIRs, but unlike FLIRs they are designed to be able to measure
the apparent temperature at the target surface and to produce quantitative thermo-
grams. They represent the most recent developments in FPA imagers and are avail-
able in compact, lightweight, battery operated configurations.
IRFPA cameras offer thermal resolution comparable to or better than opto-me-
chanically scanned imaging radiometers (0.02–0.2°C) and considerably better spatial
resolution (1 mrad or better with standard optics). At this writing, both qualitative
(measuring) and quantitative (non-measuring) IRFPA cameras are commercially
available, using both cooled and uncooled arrays, in a wide variety of configurations
and operating over a broad selection of spectral regions. With inherently faster re-
sponse, no moving parts and superior spatial resolution, IRFPA cameras have re-
placed opto-mechanically scanned imagers for virtually all applications.
Figure 2.20 is a schematic diagram of an IRFPA camera based on bolometric IR
detectors.
Modern IRFPA thermal imagers provide quantitative temperature measuring
capability and high resolution image quality. Detector cooling is sometimes re-
quired and this is most often accomplished by means of a thermoelectric, or Peltier
effect, cooler or an electric-powered Stirling-cycle nitrogen or helium cooler.

2.3.4 IRFPA detectors

The IRFPA detector is the heart of a thermal imaging system, and selecting the right
camera is crucial to the success of the thermographer’s mission. Today’s thermogra-
pher is the beneficiary of decades of IR detector development, engendered by the
needs of military and space programs. With the development of new detectors, the
choices become even wider, as illustrated by the spectral response curves of Fig. 2.16.
When selecting an instrument for an application, it is important to understand that the
detector is a limiting factor in the performance of the instrument as follows:

Figure 2.20 Infrared focal plane array camera schematic (courtesy of Honeywell, Inc.).
Basics of Noncontact Thermal Measurements 29

· The spatial resolution of the instrument can be no better than that allowed by
the detector.
· The spectral range of the instrument can be no broader than that of the detector.
· The thermal sensitivity of the instrument can be no better than that of the detector.
· The speed of response of the instrument can be no faster than that of the detector.

The newest and perhaps most versatile of the detectors shown is the QWIP array.
QWIP detectors are made from gallium arsenide (GaAs) material. These detectors
are narrow-band, high-speed, high-sensitivity detectors that can be designed to op-
erate in selected narrow bands from the MWIR (2–5 µm) to the LWIR (8–14 µm).
The versatility of this detector, as well as others, will be illustrated in the applica-
tions chapters in Part II of this text.

2.3.5 Pyroelectric vidicon thermal imagers

These instruments have also been superceded by instruments using two-dimensional
IR focal plane staring arrays, although there are some pyrovidicon imagers still in
use. For reference purposes, the following description and illustration are provided.
A pyroelectric vidicon or pyrovidicon is a video camera tube that operates in the
IR (2–20 µm) region instead of the visible spectrum. Electronically scanned ther-
mal imaging systems based on pyrovidicons and filtered to operate in the 8–14 µm
atmospheric window provide qualitative thermal images and are classified as ther-
mal viewers. Figure 2.21 is a cross-sectional schematic of a pyrovidicon camera
tube used in pyrovidicon imagers. The output of the pyrovidicon tube is compatible
with standard video processing electronics.
Published performance characteristics of commercially available IR thermal
imaging systems can be found in Appendix A. Detailed discussions of diagnostic
software and image recording methods can be found in Chapter 4.

Figure 2.21 Pyrovidicon camera tube schematic (courtesy of MSA, Inc.).

30 Chapter 2

Table 2.1 Temperature conversion chart.

Table Use Instructions

1. Start in the Temp. column and find the temperature you wish to convert.
2. If the temperature to be converted is in degrees C, scan to the right column for the de-
grees F equivalent.
3. If the temperature to be converted is in degrees F, scan to the left column for the de-
grees C equivalent.
Conversion Factors
°C = (°F – 32)/1.8 0 Kelvin = –273.16°C
°F = (°C ´ 1.8) + 32 0 Rankine = –459.69°F

°C Temp. °F °C Temp. °F °C Temp. °F

101 150 238 36.7 34 29.2 26.7 16 3.2
95.6 140 220 36.1 33 27.4 26.1 15 5
90 130 202 35.6 32 25.6 25.6 14 6.8
84.4 120 184 35 31 23.8 25 13 8.6
78.9 110 166 34.4 30 22 24.4 12 10.4
73.3 100 148 33.9 29 20.2 23.9 11 12.2
67.8 90 130 33.3 28 18.4 23.3 10 14
62.2 80 112 32.2 26 14.8 22.8 9 15.8
56.7 70 94 31.7 25 13 22.2 8 17.6
51.1 60 76 31.1 24 11.2 21.7 7 19.4
45.6 50 58 30.6 23 9.4 21.1 6 21.2
40 40 40 30 22 7.6 20.6 5 23
39.4 39 38.2 29.4 21 5.8 20 4 24.8
38.9 38 36.4 28.9 20 4 19.4 3 26.6
38.3 37 34.6 28.3 19 2.2 18.9 2 28.4
37.8 36 32.8 27.8 18 0.4 18.3 1 30.2
37.2 35 31 27.2 17 1.4 17.8 0 32
17.2 1 33.8 2.8 27 80.6 11.7 53 127.4
16.7 2 35.6 2.2 28 82.4 12.2 54 129.2
16.1 3 37.4 1.7 29 84.2 12.8 55 131
15.6 4 39.2 1.1 30 86 13.3 56 132.8
15 5 41 0.6 31 87.8 13.9 57 134.6
14.4 6 42.8 0 32 89.6 14.4 58 136.4
13.9 7 44.6 0.6 33 91.4 15 59 138.2
13.3 8 46.4 1.1 34 93.2 15.6 60 140
Basics of Noncontact Thermal Measurements 31

Table 2.1 continued

°C Temp. °F °C Temp. °F °C Temp. °F

12.8 9 48.2 1.7 35 95 16.1 61 141.8
12.2 10 50 2.2 36 96.8 16.7 62 143.6
11.1 12 53.6 2.8 37 98.6 17.2 63 145.4
10.6 13 55.4 3.3 38 100.4 17.8 64 147.2
10 14 57.2 3.9 39 102.2 18.3 65 149
9.4 15 59 4.4 40 104 18.9 66 150.8
8.9 16 60.8 5 41 105.8 19.4 67 152.6
8.3 17 62.6 5.6 42 107.6 20 68 154.4
7.8 18 64.4 6.1 43 109.4 20.6 69 156.2
7.5 19 66.2 6.7 44 111.2 21.1 70 158
6.7 20 68 7.2 45 113 21.7 71 159.8
6.1 21 69.8 7.8 46 114.8 22.2 72 161.6
5.6 22 71.6 8.3 47 116.6 22.8 73 163.4
5.0 23 73.4 8.9 48 118.4 23.3 74 165.2
4.4 24 75.2 10 50 122 23.9 75 167
3.9 25 77 10.6 51 123.8 24.4 76 168.8
3.3 26 78.8 11.1 52 125.6 25 77 170.6
Chapter 3

Matching the Instrument

to the Application

To select an instrument suitable to a particular application, the user needs to under-

stand how to determine and specify its required performance. This chapter dis-
cusses the performance parameters of radiation thermometers and IR cameras
(point-sensing instruments and scanning and imaging instruments respectively)
and their significance in solving applications.
Since IR cameras are essentially extensions of radiation thermometers, I will
demonstrate that many of the parameters are common to both.

3.1 Radiation Thermometers (Point-Sensing Instruments)

For radiation thermometers the following performance parameters should be con-
sidered:

· Temperature range: The high and low limits over which the target temperature
may vary.
· Absolute accuracy: As related to the National Institute of Standards and Tech-
nology (NIST) standard.
· Repeatability: How faithfully a reading is repeated for the same target.
· Temperature sensitivity: The smallest target temperature change the instrument
needs to detect.
· Speed of response: How fast the instrument responds to a temperature change at
the target surface.
· Target spot size and working distance: The size of the spot on the target to be
measured and its distance from the instrument.
· Output requirements: How the output signal is to be utilized.
· Spectral range: The portion of the IR spectrum over which the instrument will
operate.
· Sensor environment: The ambient conditions under which the instrument will
operate.

Temperature range and absolute accuracy will always be interrelated. For example,
the instrument might be expected to measure a range of temperatures from 0 to

33
34 Chapter 3

200°C with an absolute accuracy ±2°C over the entire range. This could alternately
be specified as ±1% absolute accuracy over full scale. On the other hand, we might
require the best accuracy at some specific temperature, say 100°C. In this case the
manufacturer should be so informed. The instrument can then be calibrated to accu-
rately match the manufacturer’s laboratory calibration standard at that temperature.
Since absolute accuracy is based on traceability to the NIST standard, it is difficult
for a manufacturer to comply with a tight specification for absolute accuracy. An
absolute accuracy of ±0.5°C ±1% of full scale is about as tight as can be reasonably
specified. Repeatability, on the other hand, can be more easily assured by the manu-
facturer and is usually more important to the user.
Temperature sensitivity is also called “thermal resolution” or “noise equivalent
temperature difference” (NETD). It is the smallest temperature change at the target
surface that we must clearly sense at the output of the instrument. This is almost al-
ways closely associated with the cost of the instrument, so unnecessarily fine tem-
perature sensitivity should not be specified. An important rule to remember is that
for any given instrument target sensitivity will improve for hotter targets where
there is more energy available for the instrument to measure. We should specify
temperature sensitivity, therefore, at a particular target temperature, and this should
be near the low end of the range of interest. We might, for example, specify temper-
ature sensitivity to be 0.25°C at a target temperature of 25°C, and be confident that
the sensitivity of the instrument will be at least that for targets hotter than 25°C.
Speed of response is generally defined as the time it takes the instrument output
to respond to 95% of a step change at the target surface. Figure 3.1 shows this
graphically. Note that the sensor time constant is defined by convention to be the
time required to reach 63% of a step change at the target surface. Instrument speed
of response is about five time constants, and is generally limited by the detector
used. As previously discussed, this limit is on the order of microseconds for
photodetectors and milliseconds for thermal detectors. There is, however, a tradeoff

Figure 3.1 Instrument speed of response and time constant.

Matching the Instrument to the Application 35

between speed of response and temperature sensitivity. As in all instrumentation

systems, as the speed of response becomes faster (wider information bandwidth)
the sensitivity becomes poorer (lower signal-to-noise ratio). We learn from this that
speed of response should not be overspecified.
Target spot size (also called spatial resolution) and working distance may be
specified as just that: 1 cm at 1 m, for example. Spot size is the projection of the sen-
sitive area of the detector at the target plane. We can express spot size in more gen-
eral terms such as FOV angle (10 mrad, 1 deg, 2 deg) or a FOV (spot size to working
distance) ratio (D/15, D/30, D/75). A D/15 ratio means that the instrument mea-
sures the emitted energy of a spot 1/15 the size of the working distance, for exam-
ple, 3 cm at 45 cm. These relationships are illustrated in Fig. 3.2, which includes a
quick method of calculating spot size based on working distance and manufacturer
furnished FOV information. Figure 3.3 illustrates FOVs of several instruments and
shows how an instrument can be selected based on the required spot size and work-
ing distance. An examination of the collecting beams of the instruments shown also
shows that, at very close working distances, this simple D/x ratio does not always
apply. If close-up information is not clearly provided in the product literature, the
instrument manufacturer should be consulted. For most applications the approach
in Fig. 3.2 will be suitable.
The output requirements are totally dependent on the user’s needs. If a readout
indicator is required, a wide selection is usually offered. An analog output suitable
for recording, monitoring and control is commonly provided. In addition, most
manufacturers offer a broad selection of output functions, including digital [binary
coded decimal (BCD) coded] outputs, high, low, and proportional set points, signal
peak or valley sensors, sample and hold circuits, and even closed-loop controls for
specific applications. Many presently available instruments, even portable hand-
held units, include microprocessors that provide many of the above functions on
standard models.

Figure 3.2 Instrument FOV determination.

36 Chapter 3

Figure 3.3 Fields of view of IR radiation thermometers (courtesy of Raytek, Inc.,

a Fluke company).
Matching the Instrument to the Application 37

As previously noted, the operating spectral range of the instrument is often

critical to its performance. For cooler targets, up to about 500°C, most manufactur-
ers offer instruments operating within the 8–14 µm atmospheric window. For hotter
targets shorter operating wavelengths are selected, usually shorter than 3 µm. One
reason for choosing shorter wavelengths is that this enables manufacturers to use
commonly available and less expensive quartz and glass optics, which have the
added benefit of being visibly transparent for more convenient aiming and sighting.
Another reason is that estimating effective emissivity incorrectly will result in
smaller temperature errors when measurements are made at shorter wavelengths.
A good general rule to follow, particularly when dealing with targets of low or un-
certain emissivities, is to work at the shortest wavelengths possible without compro-
mising sensitivity or risking susceptibility to reflections from visible energy sources.
Spectrally selective instruments may employ interference filters to allow only a
very specific broad or narrow band of wavelengths to reach the detector. (A spec-
trally selective detector or a combination of a spectrally selective detector and a fil-
ter may also be used.) This can make the instrument highly selective to a specific
material whose temperature is to be measured in the presence of an intervening me-
dium or an interfering background.
Say, for example, the objective is to measure the temperature of objects from
200–1000°C inside a heating chamber with a glass port, or inside a glass bell jar. An
instrument operating in the 1.5–2.5 µm band will “see” through the glass and make
the measurement easily.
A very important generic example of the need for spectral selectivity is in the
measurement of plastics in process being formed into films and other configura-
tions. Thin films of many plastics are virtually transparent to most IR wavelengths,
but do emit at certain wavelengths. Polyethylene, polypropylene, and other related
materials, for example, have a very strong, though narrow, absorption band at
3.45 µm. Polyethylene film is formed at about 200°C in the presence of heaters that
are at about 700°C. Figure 3.4 shows the transmission spectra of 1.5 mil-thick poly-
ethylene film and the narrow absorption band at 3.45 µm. The instrument selected
for measuring the surface of the film has a broadband thermal detector and a
3.45-µm spike band-pass filter. The filter makes the instrument blind to all energy
outside of 3.45 µm and enables it to measure the temperature of the surface of the
plastic film without seeing through the film to the heaters.
Figure 3.5 shows a similar solution for 0.5 mil-thick polyester (Mylar) film un-
der about the same temperature conditions. Here the strong polyester absorption
band from 7.7–8.2 µm dictates the use of a 7.9-µm spike filter placed in front of the
same broadband detector.

3.2 Infrared Cameras—Qualitative and Quantitative

The parameters used for assessing the performance of IR cameras are complex and
the methods used for testing performance have generated some controversy among
manufacturers and users of these instruments.
38 Chapter 3

Figure 3.4 Measuring temperature of polyethylene (courtesy of Barnes Div., Good-

year Corp.).

Figure 3.5 Measuring temperature of polyester (courtesy of Barnes Div., Goodyear

Corp.).

Since a thermal image is made up of a great number of discrete point measure-

ments, however, many of the performance parameters of IR thermal imagers are the
same as those of radiation thermometers (point sensing IR radiometers that read out
in temperature). Others derive from, or are extensions of, radiation thermometer
performance parameters.
Matching the Instrument to the Application 39

Qualitative cameras, also called thermal viewers, differ from quantitative cam-
eras, also called imaging radiometers, in that thermal viewers do not provide tem-
perature or thermal energy measurements. Therefore, some of the parameters
discussed will be of little importance to users who require qualitative rather than
quantitative thermal images.
To aid in camera selection, a detailed comparison of imager performance pa-
rameters is provided in Sec. 4.4.2.3. In this section, five categories of instruments
available in today’s commercial thermal imager market are compared, including
suggested applications for each.

3.2.1 Performance parameters of quantitative cameras

The Infrared Handbook (The Environmental Research Institute of Michigan, 1985)
provides an extensive table of terms and definitions (Sec. 19.1.2) and a list of speci-
men specifications (Sec. 19.4.1). The section of the handbook covering IR imaging
systems does not, however, deal with the imager as a quantitative measurement in-
strument, so the performance parameters related with temperature measurement
must be added. From the user’s point of view, some simplifications can be made
which result in some acceptable approximations. Bearing these qualifications in
mind, the following definitions of the key performance parameters of IR quantita-
tive cameras are offered:

· Total field of view (TFOV): The image size, in terms of scanning angle.
(Example: TFOV = 20°V ´ 30°H)
· Instantaneous field of view (IFOV): The angular projection of the detector ele-
ment at the target plane: Imaging spatial resolution.
(Example: IFOV= 2 mrad) (mrad means milliradians)
· Measurement spatial resolution (IFOVmeas or MFOV): The spatial resolution
describing the minimum target spot size on which an accurate temperature
measurement can be made.
(Example: IFOVmeas = 2 mrad)
· Frame repetition rate: The number of times every point on the target is scanned
in one second.
(Example: frame rate = 30 frames/second)
· Minimum resolvable temperature (MRT): The smallest blackbody equivalent
target temperature difference that can be observed: temperature sensitivity.
(Example: MRT = 0.1°C at 25°C temp.)

It shall be seen that MRT and the terms relating to spatial resolution are interrelated
and cannot be considered independently. Other parameters such as spectral ranges,
target temperature ranges, accuracy and repeatability, and focusing distances are
essentially the same as those defined previously for IR radiation thermometers, al-
though they may be expressed differently. Dynamic range and reference level
range, for example, are the terms that define the target temperature ranges for IR
40 Chapter 3

thermal cameras. While the operating spectral range of a radiation thermometer is

often critical to its performance, the spectral range of operation of a thermal camera
is not usually critical to the user. Almost all commercial thermal cameras operate in
either the 2–5 µm or the 8–12 µm atmospheric window, depending on the manufac-
turer’s choice of detector and detector cooling method. Filter wheels or slides are
usually available so that users can insert special interference filters and perform
spectrally selective measurements when necessary.
Despite some manufacturers’ claims to the contrary, there is usually little differ-
ence in overall quality of performance between a camera operating in the 2–5 µm
band and a camera operating in the 8–12 µm band, all other parameters being equal.
For a specific application, however, there may be a clear choice. One example of this
would be selecting a camera operating in the 2–5 µm band to observe a target through
a quartz window. Since quartz is virtually opaque in the 8–12 µm region, there would
be no alternative. Another example would be selecting a camera operating in the
8–12 µm band to observe a cool target through a long atmospheric path. Since long
path atmospheric absorption is much greater in the 2–5 µm than in the 8–12 µm win-
dow, the choice would be obvious.
For thermal viewers, parameters relating to temperature range are only applica-
ble in the broadest sense; absolute accuracy and stability parameters are not appli-
cable; MRT is applicable only as an approximation since stability cannot be
assured; IFOVmeas is not applicable.
Secondary features such as field uniformity and spatial distortion are design pa-
rameters, and are assumed to be handled by responsible manufacturers.
A discussion of the significant performance parameters (figures of merit) of IR
cameras follows.

3.2.1.1 Total field of view (TFOV) and instantaneous field of view (IFOV)
The TFOV of an IR Camera is, essentially, the projection of the focal plane detector
array at the target surface, and the IFOV is the projection of a single detector ele-
ment. TFOV and IFOV are illustrated in Fig. 3.6 that also describes how the total
target size and imaging spatial resolution at any given working distance may be cal-
culated from manufacturer’s specifications.

3.2.1.2 Temperature sensitivity: MRTD or MRT

Temperature sensitivity, also called thermal resolution or NETD for a radiation
thermometer, is the smallest temperature change at the target surface that can be
clearly sensed at the output of the instrument. For an imaging system, the term mini-
mum resolvable temperature (MRT) or minimum resolvable temperature difference
(MRTD) defines temperature sensitivity but also implies spatial resolution (IFOV).
MRTD is expressed as a function of angular spatial frequency.
For many years the test for MRTD has been accomplished by means of a subjec-
tive procedure developed by the Department of Defense community. This involves
Matching the Instrument to the Application 41

Figure 3.6 TFOV and IFOV of an IR camera.

selecting the smallest (highest frequency) standard periodic test pattern (four bars,
7:1 length to width aspect ratio) that can be distinguished as a four-bar contrast target
by the observer, and recording the smallest detectable element-to-element tempera-
ture difference between two blackbody elements on this pattern. Unlimited viewing
time and optimization of controls are allowed; and for scanning radiometers, the tar-
get is oriented with the bars normal to the fast scan (line scanning) direction. Fig-
ure 3.7 illustrates the setup using an ambient pattern and a heated background. The
MRTD curve shown is a function of spatial frequency (cycles/mrad). Additional
points on the curve are achieved by changing the pattern size or the distance to the
scanner. This subjective approach, while originally developed for opto-mechanically
scanned cameras, is equally valid for the new staring FPA cameras.

3.2.1.3 Imaging spatial resolution and instantaneous FOV

For thermal imagers, the IFOV expresses spatial resolution for imaging purposes
but not for measurement purposes. Measurement instantaneous field of view
(IFOVmeas or MFOV) expresses spatial resolution for measurement purposes. The
modulation transfer function (MTF) is a measure of imaging spatial resolution.
Modulation is a measure of radiance contrast and is expressed:

V max – V min
Modulation = .
V max + V min

Modulation transfer is the ratio of the modulation in the observed image to that in the
actual object. For any system, MTF will vary with scan angle and background.
A methodology was established by the military and accepted by manufacturers and
users alike, to measure the MTF of an imager and, thereby, to verify the spatial resolu-
tion for imaging (night vision) purposes. A sample procedure is illustrated in Fig. 3.8
42 Chapter 3

Figure 3.7 Test setup for MRTD measurement and MRTD curve (courtesy of FLIR Sys-
tems, Inc.).

MTF (modulation transfer function) =

Figure 3.8 Test setup for MTF measurement.

Matching the Instrument to the Application 43

for a system where IFOV is specified at 2.0 mrad using the same setup as illustrated in
Fig. 3.7. The procedure is as follows:
A standard four-bar (slit) resolution target (7:1 aspect ratio) with a 2-mm slit
width is placed in front of a heated blackbody reference surface (blackbody refer-
ence sources are described in Sec. 5.2.1) at a distance of 1 m from the primary optic
of the instrument (The ratio of the 2 mm slit width to the 1 m working distance is 2
mrad). The target is centered in the scanned field and oriented so that a single
line-scan output can be produced normal to the slit, and this output is monitored.
The analog signal value of the four peaks (Vmax), as the slits are scanned, and the an-
alog signal value of the three valleys (Vmin) are recorded using the bar target surface
ambient temperature as a base reference. The MTF is (Vmax – Vmin)/ (Vmax + Vmin). If
this is at least 0.35, the 2 mrad IFOV is verified.
Some users and manufacturers disagree regarding the acceptable minimum
value of MTF to verify imaging spatial resolution, with values varying between
0.35 and 0.5 depending on the manufacturer and the purpose of the instrument. For
most users a tested value of MTF of 0.35 for a slit width representing a specified
spatial resolution is generally considered sufficient to demonstrate that spatial reso-
lution for imaging purposes. Both MRTD and MTF are functions of spatial fre-
quency for any given system. This is illustrated in Fig. 3.9, for a typical system
rated by the manufacturer to be 1 milliradian. The cutoff frequency is where the
IFOV equals one cycle (one bar and one slit) so that the intersection of the two
curves at the half-cutoff frequency represents the actual performance of the system
for an MRTD of 1°C. MTF is seen to be about 0.22 for this system.

3.2.1.4 Measurement spatial resolution (IFOVmeas or MFOV) for

opto-mechanically scanned imagers
For measurement purposes, of course, the slit width should, ideally, be increased
until the modulation reaches unity. For this reason the MTF method was found to be
unsatisfactory for commercial thermal imagers where quantitative temperature
measurement and control are often necessary. Another procedure called the slit re-
sponse method was developed for this purpose and is generally accepted for mea-
suring IFOVmeas for opto-mechanically scanned cameras. In this method,
illustrated in Fig. 3.10, a single variable slit is placed in front of a blackbody source
and the slit width is varied until the resultant signal approaches the signal of the
blackbody reference. The curve shown is the slit response function (SRF). Since
there are other errors in the optics and the 100% level of SRF is approached rather
slowly, the slit width at which the SRF reaches 0.9 is usually accepted as the
IFOVmeas. Figures 3.7 and 3.10 are reprinted from C. Ohman’s paper, “Measure-
ment versus imaging in thermography,” Proc. Fifth IRIE, bk. 2, p. 65 (1985), which
provides a detailed description of setup for the slit response method, and a discus-
sion of imaging and measurement spatial resolution figures of merit.
44 Chapter 3

Figure 3.9 MRTD and MTF for a system rated at 1 mrad. (Reprinted with permission
from J. M. Lloyd, Thermal Imaging Systems, Plenum Press, 1975.)

Figure 3.10 Test setup for slit response function (courtesy of FLIR Systems, Inc.).
Matching the Instrument to the Application 45

3.2.1.5 Measurement spatial resolution (IFOVmeas or MFOV)

for FPA imagers
Since the configuration of a FPA camera differs from that of an opto-mechanically
scanned camera, the slit response test has shortcomings in determining IFOVmeas for
an FPA camera (also known as MFOV). It has been replaced by a two-dimensional ap-
proach more suitable to the FPA configuration. In this approach, known as the hole re-
sponse method, the variable slit is replaced by a series of precision apertures. These
apertures are placed, in turn, across the FOV between the camera and an extended ref-
erence source. The aperture size is increased until the aperture selected is large enough
to provide a predetermined percentage of the reference source signal (90 or 95%) at the
camera output. The IFOVmeas for the instrument under test is then calculated based on
the ratio of the diameter of the selected aperture (D) to the working distance to the aper-
ture (d). This is illustrated in Fig. 3.11.
A typical plot of the hole response function for a camera with a 120 ´ 120 ele-
ment FPA detector is illustrated in Fig. 3.12. For this camera, MFOV reaches 95%
when a = D/d = 8.2 mrad.

3.2.1.6 Speed of response and frame repetition rate

The speed of response of a radiation thermometer is generally defined as the time it
takes the instrument output to respond to 95% of a step change at the target surface
(about 5 time constants). This parameter is not applicable to thermal imagers,
where each element of the target surface is scanned so rapidly that the value for an
individual element may never reach 95% of the element-to-element contrast during
a single-frame scan. Frame integration techniques are used to improve measure-
ment precision, and image quality as well, where it is critical.
Frame repetition rate is the measure of data update of a thermal imager. It is the
number of times per second every element is scanned. Frame repetition rates of

Figure 3.11 Hole response method for determination of IFOVmeas (MFOV) for
FPA-based cameras.
46 Chapter 3

Figure 3.12 Plot of hole response function for an FPA-based camera where MFOV is
measured at 8.2 mrad (courtesy of FLIR Systems, Inc.).

30 Hz are typical for general purpose IR cameras. Frame repetition rates of over
1000 Hz are available in special purpose cameras.
(For opto-mechanically scanned imagers, this is not the same as field repetition
rate. Manufacturers of these cameras tended to use fast field rates with not all the
scan lines included in any one scan, and then interlace the fields so that it would
take multiple fields to complete a full frame. This produces a more flicker-free im-
age and is more pleasing to the eye than scanning full data frames at a slower rate.)

3.2.2 Performance parameters of qualitative cameras

For quantitative cameras, as previously mentioned, parameters relating to tempera-
ture range are only applicable in the broadest sense. Absolute accuracy and stability
parameters are not applicable; MRT is applicable only as an approximation since
stability cannot be assured and IFOVmeas is not applicable. Otherwise, all perfor-
mance parameters relating to quantitative imaging cameras are applicable to quali-
tative imaging cameras.

3.3 Thermal Imaging Software

In order to optimize the effectiveness of thermographic measurement programs the
thermographer needs a basic understanding of thermal image processing tech-
niques. The following is a broad discussion of thermal image processing and diag-
nostics. A more detailed description of currently available thermal imaging and
diagnostic software is provided in Chapter 4.
Thermal imaging software can be categorized into the following groupings:

· Quantitative thermal measurements of targets.

· Detailed processing and image diagnostics.
· Image recording, storage, and recovery.
Matching the Instrument to the Application 47

· Image comparison.
· Archiving and database development; report preparation.*

With the introductio of computer-assisted thermal image storage and processing,

thermography has become a far more exact science and the ability to perform image
analysis and trend analysis has greatly expanded its reach. Innovative software has
been tailored specifically for detailed image and thermal data analysis, and has
been rapidly updated and expanded.
Most software packages for thermographic image analysis and diagnostics of-
fer a number of standard features. These include spot temperature readout, multiple
X and Y analog traces, monochrome and multiple color scale selection, image shift,
rotation and magnification, area analysis with histogram display, image averaging
and filtering and permanent disk storage and retrieval. Some of these capabilities
are offered as part of the basic instrument and some are found in a diagnostics pack-
age offered separately. The newest field-portable instruments allow the thermogra-
pher to store images to disk during field measurements and perform detailed image
analysis upon return to home base.
The ability to perform differential thermography is a powerful feature of
thermographic software routines. This is the capability for archiving thermal im-
ages of acceptable operating components, assemblies and mechanisms, and using
these stored images as models for comparison to subsequently inspected items.
Subtractive routines produce differential images illustrating the deviation of each
pixel (picture element) from its corresponding model.
Another powerful routine recently introduced is an emissivity determination
and correction program which produces true surface temperature thermograms of
microelectronic devices and other very small targets. To perform this function, the
unpowered device is heated sequentially to two known low-level temperatures and
the stored thermal images are used to allow the computer to calculate the emissivity
of each pixel. The device is then powered and the image produced is corrected,
point-by-point, for the emissivities previously computed. There is great interest in
applying this spatial emissivity correction to larger targets such as circuit cards. The
difficulty in developing a reliable emissivity matrix lies in achieving tight control
over the temperature and temperature uniformity while heating a target of this size.
For the professional thermographer, the maintenance of an historical database
is most critical, and thermographic software allows this to be done systematically.
The historical data included with stored images (time, date, location, ambient con-
ditions, distance to target, emissivity setting, scanner serial number, and additional
stored comments) serve as important inpunts and subsequent backup for the written
report.

*
Although data and image database development is not an exclusive characteristic of thermal imaging
software, it should be considered an important part of the thermographer’s toolkit.
48 Chapter 3

3.4 Thermal Image Fusion Techniques

Thermal image fusion is defined as the fully registered combination of a thermal
image with another mode of image for the purpose of providing an enhanced single
view of a scene with extended information content. Most commonly in thermo-
graphy, a thermal image is fused with a visible image for dramatically improved
recognition and location of thermal anomalies. A more detailed description of cur-
rently available thermal image fusion capabilities is provided in Chapter 4, and ap-
plication examples are provided in later chapters.
Chapter 4

Instruments Overview

4.1 Introduction and Classification of Instruments

This chapter begins with a classification of IR sensing and imaging instruments by

type and application, listing commercially available instruments, from single-point
radiation thermometers, to line scanners, to high-speed, high-resolution thermal
imaging cameras.
A detailed discussion of performance characteristics and features follows,
along with a discussion of typical thermographic display approaches utilized by
various imager manufacturers. This is followed by a discussion of currently avail-
able thermographic image archiving, processing and report preparation software.
Finally, a tabulation of currently available instruments by category and manu-
facturer is appended, including a digest of performance characteristics and features.
A current index of manufacturers’ websites, addresses and phone numbers is also
appended.
Infrared sensing instruments are traditionally classified into three groups;
point-sensing, line-scanning, and thermal imaging. Point-sensing devices—com-
monly called infrared radiation thermometers—collect radiant energy from a spot
or area on the surface of an object to be measured (the target) and provide an output
indication, usually in terms of target temperature. Line-scanning instruments pro-
vide an output, generally an intensity-modulated signal, of the radiant energy (or, in
ideal cases, temperature) distribution along a single straight-line projection from
the target surface. Thermographic instruments—commonly called infrared cam-
eras—provide a digitized image, or thermal map, of the energy distribution over an
area on the target surface that is presented in the form of an intensity-modulated
black-and-white image or a synthesized color display. Point sensors and cameras
can be further divided into subgroups. Commercially available instruments in these
categories are as follows:

1. Point sensors:
· Infrared thermocouples and probes
· Portable (hand-held) instruments
· On-line monitors and controls
· Special instruments
2. Line scanners

49
50 Chapter 4

3. Cameras:
· Cameras, nonmeasuring (thermal viewers)
· Cameras, measuring (thermographic imagers)
· Special instruments

4.2 Instrument Manufacturers

Particularly in the point-sensing category, many companies offer the same instru-
ment under different private labels. In order to avoid duplication, the original man-
ufacturer or prime distributor will be listed whenever possible.
The charts in Appendix A provide a tabulation of all instruments known to the
author on which descriptive literature was available at the time of preparation of
this text. The performance characteristics are summarized rather than presented in
detail. For detailed performance information, the listed manufacturer should be
contacted. Appendix B is a listing of current websites, addresses and phone num-
bers of equipment manufacturers listed in Appendix A. The following discussions
will highlight the applications for which each instrument category and group is par-
ticularly suited based on configuration or performance characteristics. Applica-
tions themselves are discussed in detail in Chapters 6 through 12.

4.3 Discussion of Instruments

4.3.1 Point sensors (radiation thermometers)
4.3.1.1 Infrared thermocouples and probes
Infrared thermocouples are noncontacting devices, comprising an IR sensor and
lens, and providing a signal emf output proportional to the radiant exitance of a
point on a target. The solid state sensors operate on thermoelectric principles and
therefore require no bias or supply power. Infrared thermocouples are offered in
narrow temperature range segments (70–104°C, for example) and are designed to
be electrically interchangeable with specific contact thermocouples (type J, K, T, or
E, for example). While perhaps not considered instruments in the strictest sense,
these devices are simple to use, are used extensively in industrial applications, and
are worth studying as part of a thermographer’s toolbox. Numerous configurations
of IR thermocouples are commercially available, with prices ranging from less than
$100 to $800 (U.S.). An excellent review of IR thermocouples can be found in
Omega Engineering’s (Stamford, CT) Temperature Handbook, Volume E.
Temperature probes are portable spot-measuring instruments that can be a sim-
ple combination of an IR thermocouple and a readout device. They are character-
ized by a low price (from under $100 to $1,500), pocket portability, and a wide
collecting angle. They are battery powered and are generally optically preadjusted
for minimum spot size at a short working distance (a 1/4-in. spot at a 3/4-in. work-
ing distance is typical). Some models are designed to operate in a conventional
Instruments Overview 51

multimeter and some incorporate their own readout box with an LCD display. They
usually feature disposable batteries and some models have AC adapters. Tempera-
ture ranges are from about 0°F or slightly below to 600°F, and a sensitivity of ±1°F
is easily achieved. Emissivity adjustments are available on some models.
Probes are ideal for close-up measurements and find applications in circuit
board analysis, troubleshooting of electrical connections, inspection of plumbing
systems, and a variety of biological and medical studies. Most recently, consumer
versions of these devices have emerged for home use at extremely low prices. One
example is an IR ear thermometer to measure body temperature, available at phar-
macies for under $25.

4.3.1.2 Portable hand-held instruments

With some exceptions, portable hand-held instruments are pistol-shaped and de-
signed for middle-distance measurements. They are usually optically preadjusted
for infinity focus. A typical 2-deg FOV resolves a 7.5 cm (3 in.) spot at a 150 cm
(60 in.) working distance and a 30 cm (1 ft.) spot at a 9 m (30 ft.) working distance.
Prices range from under $200 to more than $3,500. Sighting and aiming methods
vary from simple aiming notches to enclosed illuminated reticles. Projected visible
laser beams are used in some models as aiming aids, to illuminate the center of the
spot being measured. There are instruments with extremely narrow FOVs (0.5 deg)
that include a rifle stock and telescopic sight. Most instruments in this group incor-
porate emissivity adjustments and some include microcomputers with limited
memory and datalogging capabilities. Most are available with a recorder output, al-
though this feature is seldom used. A meter is always provided, and the readout is
always in temperature units with one exception that reads in BTU/ft2-h. Digital
readouts featuring LEDs were introduced first but the LCD display is now used al-
most universally because its tiny power drain extends battery life. Therefore, most in-
struments offer replaceable rather than rechargeable batteries, and battery life
approaches one year. Some instruments in this group have zeroing adjustments, and
most include autozeroing features. Temperature ranges are typically from 0–1500°C.
Temperature sensitivity and readability are usually 1°(C or F), or 1% of scale, al-
though sensitivities on the order of 0.1°(C or F) are achievable.
This instrument group is particularly suited to applications where spot check-
ing of target temperatures is sufficient and continuous monitoring is not required.
A typical use would be for periodic maintenance checks of rotating machinery to
detect whether or not bearings are beginning to overheat. These instruments have
become an important part of many plant energy conservation programs, but are
equally useful in checking mix temperatures of food products, cosmetics, and in-
dustrial solvents. Although many of these instruments provide extremely accu-
rate readings, accuracy, like the recorder output, is less important to most users
than repeatability, ruggedness, portability, reliability, and ease of use. Some
newer models incorporate microcomputers with special features such as a data-

51
52 Chapter 4

logger, which has the capability to store as many as 60 readings for future re-
trieval and printout.

4.3.1.3 On-line monitoring and control

The one feature that distinguishes this instrument group from the others is dedi-
cated use. The instrument is generally mounted where it can measure the tempera-
ture of one specific target and remains there for the life of the instrument or the
process. With few exceptions, these instruments operate on line power. The output
signal of the instrument can be observed on a meter, used to operate a switch or re-
lay, feed a simple or sophisticated process control loop, or be used in any combina-
tion of these functions.
Early on-line instruments consisted of an optical sensing head and an electron-
ics/control readout unit at the other end of an interconnecting cable. This configura-
tion still exists to some extent, but most of the newer units feature sensing heads that
are more stable electronically, and hence more independent of the remote control
units. The trend is for these new sensors to mate with universal indicator/control units
that accept inputs from various types of industrial sensors. Infrared thermocouples, in
certain applications, might be configured to provide on-line monitoring and control
functions and, as such, the resulting instrument could fit into this category.
Because a customer selects an instrument in this group to perform a specific
task, the manufacturer usually provides a “shopping list” to the customer so that all
required features can be purchased.
Manufacturers offer sensing-head features such as variable or fixed focus,
sighting tubes, light pipes, water-coolable housings, air purge fittings, air curtain
devices, and see-through aiming with target-defining reticles. The shopping list for
the indicator/controller unit might include digital readout, BCD output, analog out-
put, single, double, or proportional set point, rate signals, sample and hold, peak or
valley sensor, and datalogger interface. Emissivity controls located in a prominent
place on a general purpose instrument are more likely to be located behind a bezel
on the sensor on these dedicated units, where they are set one time and locked.
Spectral characteristics are worth mentioning separately, although technically
they are part of the sensing-head shopping list. The spectral interval over which the
sensing head operates is selected to optimize the signal from the target, to reduce or
eliminate the effect of an interfering energy source, or to enable the instrument to
measure the surface temperature of thin films of material that are largely transpar-
ent to IR energy. This last application has made these instruments important factors
in the manufacture of thin film plastics as well as glass.

4.3.1.4 Special instruments

Several “special” categories of spot-measuring instruments are worth mentioning,

although they may, by strict definition, fit into one or more of the above categories.
Instruments Overview 53

The two-color or ratio pyrometer is one special case of on-line instrument. It is

particularly useful in high-temperature applications and in measuring small targets.
The effective emissivity of the target need not be known provided the emissivity is
constant and reflections are controlled. The target need not fill the FOV provided
the background is cool, constant, and uniform. Also, impurities in the optical path
resulting in broadband absorption do not affect the measurement since the measure-
ment is based on the ratio of energy in two spectral bands. Ratio pyrometers gener-
ally are not applicable to measurements below 500°F.
Another special case is the fiber optic-coupled thermometer, which allows in-
accessible targets to be measured by replacing the optic with a flexible or rigid fiber
optic bundle. This, of course, limits the spectral performance, and hence the tem-
perature range, to the higher values, but it has allowed temperature measurements
to be made when previously none were possible.
Another special application instrument known as the laser pyrometer incorpo-
rates a built-in laser projection system and uses the reflected energy of the active la-
ser to measure target reflectance. A built-in microcomputer calculates target
emissivity based on the measured reflectance and uses this to provide a corrected
true temperature reading. The laser pyrometer is useful for high-temperature dif-
fuse target surfaces.
Prices of instruments in the on-line control instrument group vary from less
than $1,000 for an IR switch to more than $15,000 for on-line instruments equipped
with many control features. Generally speaking, the price goes up when sensitivity,
small spot size, and speed of response are all required, and, of course, when many
shopping list items are added.

4.3.2 Line scanners

The purpose of spatial scanning is to derive information concerning the distribution

of radiant energy over a target scene. Quite often a single, straight line scanned on
the target is all that is necessary to locate a critical thermal anomaly. This can be ac-
complished by a single detector element and a scanning mirror or most recently by a
linear FPA.
Modern IR line-scanning instruments use uncooled IR linear FPAs. Here the
scan line is generated by the array and the array is moved with respect to the target
in a push broom fashion to generate a thermogram. In most applications the array is
held stationary and the target, such as a web process, is moved normal to the array
axis. This “no moving parts” approach results in reduced instrument costs and
greater reliability. The spatial resolution of the line scanner at the target plane is di-
rectly related to the number of detector elements in the linear focal plane array and
the scan angle.
All commercially available single-line scanners scan in object space so that
wide-angle scanning can be accomplished. Probably the first approach to line scan-
ning adopted commercially was in an aerial-type thermal mapper in which the line
54 Chapter 4

scanner was mounted on a moving aircraft and scanned lines normal to the direction
of motion. The outputs representing these individual scan lines were inten-
sity-modulated and serially displayed in shades of gray on a strip map, representing
the thermal map of the surface being overflown by the aircraft.
High-speed on-line commercial line scanners develop high-resolution thermal
maps by scanning normal to the motion of a moving target such as paper web or a
strip steel process. Alternately, they can be mounted on a moving platform and
made to overfly a stationary process, such as an electrolytic copper or zinc refining
tank house, at a controlled speed. The output signal information is in real-time com-
puter compatible format and can be used to monitor, control or predict the behavior
of the target. The best applications for this scanner are in on-line real-time process
monitoring and control.
Significant recent developments in this area have made families of line cameras
available, with a wide selection of linear FPA detectors based on the speed, resolu-
tion, and spectral sensitivity requirements of the process being monitored.

4.3.3 Infrared cameras (thermal imagers)

High-resolution thermal imagers featuring IRFPA detectors have completely re-
placed opto-mechanically scanned imagers, and at this writing, virtually all com-
mercially marketed IR cameras feature IRFPA detectors.
When problems in temperature monitoring and control cannot be solved by the
measurement of one or several discrete points on a target surface, it is then neces-
sary to thermally map the total area of the target surface. This is done through the
use of 2D staring FPA detectors. Each detector in the array stares at one point (or
pixel) at the target plane. The detector output is intensity-modulated in proportion
to the total exitant radiant energy at that specific point on the target surface. The im-
age produced is presented in monochrome or color where the gray shades or color
hues are intended to represent a thermal level at the target surface. As explained in
Sec. 1.3, these thermal images are called thermograms.
Thermal imagers, originally priced as high as $180,000, are now available for well
under $10,000, although special models can still cost in excess of $100,000. The new-
est offers in this category are the size and weight of a commercial video palmcorder.
As previously mentioned, the charts in Appendix A include listings of all ther-
mal imaging instruments on which descriptive literature was available when this
text was prepared. Performance characteristics are summarized as well. Appen-
dix B lists current websites, addresses, and phone numbers of the equipment manu-
facturers listed in Appendix A.
This next section discusses cameras (thermal imagers) as categorized in Sec. 4.1.

4.3.3.1 Cameras, nonmeasuring (thermal viewers)

Thermal viewers emphasize picture quality rather than measurement capability.
Most general-purpose thermal viewers use uncooled bolometric or ferroelectric de-
Instruments Overview 55

tector arrays. In the late 1990s the first thermal viewers to use uncooled FPA detec-
tors were introduced commercially, based on thermal IR night vision devices
developed for the military. The use of uncooled arrays represents a price break-
through in that some are currently priced at less than $7,000. They are used in
firefighting and driver’s aid applications as well as traditional security and night vi-
sion applications, and in a variety of predictive maintenance and building diagnos-
tics applications.
While the individual thermal detector elements are slow in response, on the or-
der of milliseconds, every one of the thousands of elements in the array is always
exposed to the incoming target radiation, and fast enough to respond fully to a typi-
cal 30-Hz video scanning rate. Initially offered to the security and law enforcement
market, these imagers continue to find their way into a wide variety of commercial
and industrial applications. Because these instruments have no measurement capa-
bilities, they are appropriately classified as thermal viewers. See Sec 4.3.3.2 for a
discussion of measuring IRFPA cameras.
For special applications where high speed, improved sensitivity, or spectral se-
lectivity is required, cooled photodetector arrays are used. These include PtSi,
InSb, HgCdTe, and most recently GaAs QWIPs, all of which require cooling. The
spectral response characteristics of these detectors are illustrated in Fig. 2.16.

4.3.3.2 Cameras, measuring (thermographic imagers)

Thermographic imagers emphasize both image quality and measurement capabil-
ity. Most general-purpose thermographic imagers (also called imaging radiome-
ters) use uncooled bolometric or ferroelectric detector arrays. These instruments
potentially provide quantitative temperature-measuring capability and high-resolu-
tion image quality. Higher performance imagers, with fast scan capabilities and
spatial resolution of up to 512 ´ 512 elements/frame or better sensitivity, often
require cooled detector arrays that for the most part use electric-powered, Stirling-
cycle, nitrogen gas coolers. All thermographic imagers provide a means for mea-
suring target surface temperature.
With few exceptions, these instruments operate within the 0.9–1.9 µm (NIR),
the 3–5 µm (MWIR), or the 8–14 µm (LWIR) atmospheric windows. In addition to
quantitative temperature-measuring capability in idealized circumstances, the gen-
eral-purpose, uncooled cameras offer excellent spatial resolution (about 1 mrad)
and minimum resolvable temperature (0.02–0.2°C). Most manufacturers also offer
isotherm graphics features, spectral filtering, interchangeable optics for different
total FOV, color, or monochrome (black and white) displays on-board image stor-
age and video recording capabilities and computer compatibility. Most gen-
eral-purpose systems in use today feature compact, field-portable, battery-operable
configurations. A complete system, including battery and image storage, can usu-
ally be handled easily by one person. Some special-purpose systems are not config-
ured for one person. Thermal imagers intended for the thermal examination of
microcircuit chips and other small devices, for example, are arranged in a bench
56 Chapter 4

type configuration. Systems designed for testing of printed circuit boards and simi-
lar targets, are also made to be integrated into a test bench with automatic test
equipment.
Base prices range from $7,000 to $25,000 for basic field-portable cameras and
up to $70,000 for special high-resolution imagers. The addition of special lenses
and computer-based diagnostic software packages can increase the price to well in
excess of $100,000.
Performance parameters continue to improve. Where the measurements are
made under controlled or laboratory conditions, extremely accurate and depend-
able measurements result. One model, the QFI InfraScope III, provides true tem-
perature measurement on microelectronics targets with full field emissivity
compensation and spot sizes down to 2.5 µm. On some portable models of FPA
imagers, it is currently possible to achieve thermal resolution better than 15 mK
(milliKelvins) (0.015°C) with imaging spatial resolution better than 3 µm on live
targets.

4.3.3.3 Performance comparisons of FPA measuring cameras

Most applications can be met by selecting from among the five categories of instru-
ments available in today’s commercial thermal imager market listed below:

1. Uncooled FPAs—the general purpose choice.

Uncooled IRFPA imagers, operating within the 7–14 µm region, are suitable for
most applications in:
· Predictive maintenance and condition monitoring
· Buildings, roofs, and infrastructure
· Process monitoring and control (except where there are high-speed or spectral
considerations)
· Medical and biological studies
· Materials evaluation and nondestructive testing (except for high-speed or
high-resolution applications)
· Security, surveillance, night vision, search and rescue, and firefighting
Typical performance characteristics of imagers in this category are:
· Temperature sensitivity (NETD): 0.08°C (80 milliKelvins) at 30°C
· Spectral range: 7.5–13 µm
· Spatial resolution: 1.3 milliradian (320 ´ 240-element microbolometric FPA)
· Frame repetition rate: 50/60 Hz
2. Mid-range (MWIR) InSb or PtSi FPAs.
Cooled PtSi or InSb imagers are preferable where spectral selectivity at shorter
wavelengths is important (such as plastic web temperature measurements) or for
high-temperature applications (such as furnace measurements).
Instruments Overview 57

Salient performance characteristics of a typical imager in this category are:

· Temperature sensitivity (NETD): 0.02°C (20 milliKelvins) at 30°C
· Spectral range: 3.4–5 µm
· Spatial resolution: 1.2 milliradian (256 ´ 256 element PtSi FPA)
· Frame repetition rate: 50/60 Hz
InSb-based imagers have somewhat better thermal sensitivity than PtSi-based
imagers and are somewhat more expensive.
3. High-speed, high-sensitivity photodetector FPAs—for special applications.
For special applications involving high-speed phenomena, high-thermal sensitiv-
ity, and processing flexibility at longer wavelengths, the detector of choice has be-
come the GaAs QWIP FPA.
Salient performance characteristics of a typical imager in this category are:
· Temperature sensitivity (NETD): 0.02°C (2 milliKelvins) at 30°C
· Spectral range: 8–9 µm
· Spatial resolution: 1.1 milliradian (320 ´ 240 element GaAs QWIP FPA)
· Frame repetition rate: selectable from 50/60 Hz to 750/900 Hz
4. NIR (near IR) FPAs—for telecommunications, fiber optic, and laser-profiling
applications.
Salient performance characteristics of a typical imager in this category are:
· Radiant sensitivity noise equivalent irradiance (NEI): 1 ´ 1010 ph/cm2/sec (be-
cause the applications for this type of instrument measure radiant power rather
than temperature, sensitivity is expressed in NEI rather than NETD)
· Spectral range: 900–1700 nm (0.9–1.7 µm)
· Spatial resolution: 1.2–1.6 milliradian (320 ´ 256 element InGaAs FPA)
· Frame repetition rate: 30 Hz
5. Special high-temperature FPA imaging pyrometers—for special high-tempera-
ture applications such as furnace temperature monitoring.
Salient performance characteristics of a typical imager in this category are:
· Temperature sensitivity (NETD): 1°C
· Spectral range: 700–1100 nm (0.7–1.1 µm) selected filters for ranges from
600–2400°C
· Spatial resolution: 1.2–1.6 milliradian (776 ´ 484 near IRFPA detector)
· Frame repetition rate: 30 Hz

4.4 Thermal Imaging Diagnostic Software

The new generation of thermal imagers features the capability to correct for field
measurement mission conditions such as working distance to the target (media at-
tenuation) and imager background temperature (ambient reflections off the target).
58 Chapter 4

These corrections can be made either at the time the measurements are made or
through post-processing corrections. Available diagnostic image-processing capa-
bilities can be generally categorized into six groups. Thermal imaging applications
often require the use of more than one of these six groups:

1. Quantitative thermal measurements of targets.

2. Detailed processing and image diagnostics.
3. Image recording, storage, and recovery.
4. Image comparison.
5. Thermal image fusion.
6. Report and database preparation.

4.4.1 Quantitative thermal measurements of targets

This is the capability of the thermal imaging system to provide the user with the true
radiance or temperature value of any point (or all points) on the target surface. For
true radiance measurements, the system throughput attenuation must be taken into
consideration as well as losses through the measurement medium (atmosphere, in
most cases). For true temperature measurement, the effective emissivity of the tar-
get must also be considered.
In order to provide true radiance values, the system calibration constants are
fed into the computer on initial setup, and a system of prompts assures the operator
that a change in the aperture setting, target distance, interchangeable lens, etc., is
fed into the computer each time a change in the operating conditions occurs. For
true temperature values the operator must insert an emissivity value for the target
and a setting for the temperature of the instrument background. The displayed tem-
perature readings then assume that the effective emissivity of the entire target sur-
face is equal to the inserted value.
In operation, a color scale (or monochrome gray scale) is provided along one
edge of the display with temperature shown corresponding to each color or gray
level. The operator can also place one or more spots or crosshairs on the image and
the temperature value of that pixel will appear in an appropriate location on the dis-
play. Some systems allow the assignment of several different values of effective
emissivity to different areas of the target selected by the operator with the resulting
temperature correction.
One system, developed for thermal imaging of semiconductor devices and
other microtargets, offers a spatial emissivity correction based on the actual mea-
surement of the effective emissivity over the surface of the target. By means of a
precision-controlled heated substage, the operator heats the unpowered device to
two known temperatures in sequence. At each temperature a radiance image is re-
corded. Using the known temperature and the known radiance for two temperatures
the effective emissivity matrix is computed, pixel-by-pixel, and stored. This matrix
is subsequently used to correct the powered radiance image of that specific device
and to provide a true temperature thermogram.
Instruments Overview 59

4.4.2 Detailed processing and image diagnostics

This section describes the capability of the computer to analyze each pixel of a ther-
mal image and to present information in a wide variety of qualitative and quantita-
tive forms for the convenience of the user. Some (but by no means all) of these
capabilities are discussed below.
In addition to the spot meter capability discussed previously, the operator may
call for profile displays. The analog trace, in x, y, or both, of the lines on the image
intersecting at the selected spot will then appear at the edge of the display. Some
systems allow the operator to display as many as seven sets of profiles simulta-
neously. Profiles of skew lines can also be displayed on some systems.
Areas can be drawn by the operator on the display in the form of circles, rectan-
gles, or point-to-point freeforms. These areas can be shifted, expanded, resized, or
rotated. They can be used to blank out or analyze portions of the image. On com-
mand, the computer will provide a detailed analysis of the entire image or the pixels
within the area, including maximum, minimum, and average values, number of pix-
els, or even a frequency histogram of the values within the area.
Although a standard (default) color scale is usually provided by the manufac-
turer, color scales can be created by the operator in almost infinite variety from as
many as 128 colors stored within the computer.
Zoom features allow the operator to expand a small area on the display for
closer examination, or to expand the colors for a small measurement range. Auto-
scale features provide the optimum display settings for any image if selected.
Three-dimensional features provide an isometric thermal contour map of the target
for enhanced recognition of thermal anomalies.

4.4.3 Image recording, storage, and recovery

Commercial thermal imaging systems have varied capabilities to index, record, and
retrieve images and data. Most systems offer limited internal image storage by
means of on-board removable computer disks (CDs), miniature flash disks, Per-
sonal Computer Memory Card International Association (PCMCIA) cards, or other
reusable storage devices. Limited image analysis software may also be incorpo-
rated into the field-portable instrument.
Images can be stored from a frozen frame thermogram of a live target on opera-
tor command, or the operator can set up an automatic sequence and a preset number
of images will be stored at preset time intervals. Most systems also offer video re-
cording options so that an entire measurement program can be recorded on video-
tape or DVD. These videos can then be played back into the system and images can
be stored on playback from videos. In addition, burst recording digital capture at
video rates (30–60 Hz) is now available from some manufacturers. Stored images
can be retrieved from storage and displayed on operator command. Current printer
technology allows the rapid printout of thermal and fused images and data, either
separately or as part of a formal report.
60 Chapter 4

Diagnostic software is generally offered separately from the basic imaging in-
strument, although some limited diagnostic software is usually included in the ba-
sic package for on-site analysis.
With the dramatic increase in media data storage capacities, the current trend
by manufacturers is to offer more and more on-board image analysis capabilities.
For extensive image storage and analysis, however, the images can be downloaded
to a computer with a large storage capacity and memory, where the extensive image
and data analysis software is resident in the computer hard drive.

4.4.4 Image comparison

This significant capability allows the automatic comparison of images taken at dif-
ferent times. The computer allows the operator to display two images, side by side
or in sequence, and to subtract one image from another, or one area from another,
and to display a pixel-by-pixel difference thermogram. This provides the capability
for archiving thermal images of acceptable components, assemblies and mecha-
nisms, and using these stored images as models for comparison to subsequently
produced items. Subtractive routines produce differential images illustrating the
deviation of each pixel (picture element) from its corresponding model. Image av-
eraging allows the computer to accumulate several scan frames and to display the
average of these frames. Comparison (subtraction) of images can be accomplished
between two real-time images, two stored images or a real-time and a stored image.

4.4.5 Thermal image fusion

Image fusion is defined as the intelligent combination of multi-modality sensor im-
agery for the purpose of providing an enhanced single view of a scene with ex-
tended information content. Thermal image fusion is the fully-registered combina-
tion of a thermal image with another mode of image for the purpose of providing an
enhanced single view of a scene with extended information content. The fusion of
thermal and visible images has become a powerful tool for the thermographer in
that it allows instant recognition of defect anomalies in even the most complex of
visual environments. Techniques for fusing images vary among manufacturers.
Both optical and digital techniques are used, which allows adjustments to the per-
cent blend to optimize the resulting image. The fully registered blending of the two
images allows the thermographer to pinpoint the exact location of thermal anoma-
lies on target surfaces. This is particularly helpful when target surfaces are either vi-
sually complex or mostly featureless.
Illustrations of the benefits of thermal image fusion are provided in later chap-
ters in the form of application examples.
Instruments Overview 61

4.4.6 Report and database preparation

Stimulated by the demand of the predictive maintenance community for timely and
comprehensive reporting of IR survey findings, most manufacturers of imaging ra-
diometers have developed comprehensive report preparation software. These pack-
ages provide templates that allow the thermographer to prepare reports in standard
word processor formats such as Word for Windows and to directly incorporate
tagged image file format (.tif), JPEG (.jpg.), bitmap (.bmp), and other digital im-
ages imported from various sources. Additional diagnostic software is customarily
provided in these packages so that post analysis and trending can be added to the re-
port.
Chapter 5

Using IR Sensing and Imaging

Instruments

5.1 Introduction: The Thermal Behavior of the Target

Manufacturers have spent a great deal of time and effort to make thermal sensing
and thermographic equipment relatively simple to operate and thermal imaging
software much easier to understand and implement. It is far simpler today than it
was ten or even five years ago for the novice thermographer to turn on the equip-
ment, aim at a target, and get an image. By the same token it is easier than ever to
misinterpret findings. For this reason, formal operator training is an important com-
ponent of a thermographic inspection program. Many equipment manufacturers
and training schools offer formal training and certification programs. See Sec. 5.4
for information on thermographer training and certification.
Operating IR instruments, especially quantitative imaging instruments, re-
quires planning, caution, and the ability to interpret the thermographic results. The
thermographer also needs a clear understanding of the thermal behavior of the tar-
gets of interest. Before beginning a measurement program, the thermographer
should address the following tasks:

· Understand the thermal behavior of the target.

· Prepare the equipment, particularly for field measurements.
· Use correct instrument operating procedures.

Ten sources of energy transfer at the target surface can cause IR thermal sensing and
imaging equipment to register apparent temperature changes. Some of these sources
represent real temperature changes at the target surface, and some do not. It is impor-
tant for the thermographer to understand these phenomena and to be able to distin-
guish between “real” and “apparent” target temperature changes. It is also important
to note that these real and apparent changes do not always occur individually, but also
may occur in combinations. Examples of the 10 sources of apparent target tempera-
ture difference are described in Secs. 5.1.1 to 5.1.10. They are tabulated as follows:

Apparent:
· Emissivity difference
· Reflectance difference

63
64 Chapter 5

· Transmittance difference
· Geometric difference

Real:
· Mass transport difference
· Phase-change difference
· Thermal capacitance difference
· Induced heating difference
· Energy conversion difference
· Direct heat transfer difference

5.1.1 Emissivity difference

As discussed in Chapter 2, the radiant energy emitted by a target surface is propor-
tional to emissivity as well as to the fourth power of the target temperature. If the
emissivity of the target surface changes, or if the wrong effective emissivity value is
assumed for the target, the apparent temperature reading will be in error. The resultant
inaccuracy will not be as a result of a real temperature change at the target surface.

5.1.2 Reflectance difference

An apparent temperature change will occur when thermal radiant energy from an ex-
ternal heat source is reflected off the target surface. The apparent change will be pro-
portional to a power of the temperature difference between the actual target and that
of the external heat source. It will also be proportional to the reflectance (1.0 minus
emissivity) of the target and to the emissivity of the external heat source. This appar-
ent change will not be as a result of a real temperature change at the target surface.

5.1.3 Transmittance difference

An apparent temperature change will occur when thermal radiant energy from an
external heat source behind the target surface is transmitted through the target sur-
face. The apparent change will be proportional to a power of the temperature differ-
ence between the actual target and that of the external heat source. It will also be
proportional to the transmittance of the target and to the emissivity of the external
heat source. This apparent change will not be as a result of a real temperature
change at the target surface.

5.1.4 Geometric difference

An apparent temperature change may occur as a result of the geometric shape of the
target. If the target surface is shaped so as to form a cavity, for example, multiple re-
flections of radiant energy among the cavity walls will result in an apparent in-
Using IR Sensing and Imaging Instruments 65

crease in emissivity. The corner of an enclosure with three mutually perpendicular

surfaces in close proximity is a good example of this. The apparent change is simi-
lar to that caused by an emissivity variation and is not as a result of a real tempera-
ture change at the target surface.

5.1.5 Mass transport difference

An example of mass transport difference is air leakage from the inside of a building
through the building surface (the target). The air in transit may heat or cool the tar-
get surface. This results in a real temperature change at the target surface.

5.1.6 Phase-change difference

An example of phase-change difference is water evaporating (changing from liquid
to gas) on or behind a target surface and temporarily cooling the surface. This re-
sults in a real temperature change at the target surface.

5.1.7 Thermal capacitance difference

An example of thermal capacitance difference is when solar heat stored in wa-
ter-saturated sections of a roof causes the surface of the roof to cool more slowly at
night, creating a contrast to the nonsaturated sections. This is because the wa-
ter-saturated sections have higher thermal capacitance than the dry sections, result-
ing in a real temperature change at the target surface.

5.1.8 Induced heating difference

An example of induced heating difference is the inductive heating of ferrous bolts
that are improperly installed in an aluminum buss bar. The magnetic field will cause
inductive heating in ferrous materials, resulting in a real temperature change at the
target surface.

5.1.9 Energy conversion difference

Most increases in temperature observed in a plant environment are as a result of en-
ergy conversion (friction to heat, chemical reaction to heat, etc.). A common example
of energy conversion difference is when the resistance of a poor connection converts
electric current to heat. This results in a real temperature change at the target surface.

5.1.10 Direct heat transfer difference

Direct heat transfer difference occurs by conduction, convection, or radiation, as
described in Chapter 2. Examples of direct heat transfer are found in nondestructive
66 Chapter 5

testing of materials where a uniform heat flow is generated, and observed thermal
anomalies indicate flaws. These are real temperature changes at the target surface.

5.1.11 Learning about the target environment

Although the thermographer’s ability to clearly identify which of the above radiant
energy-producing mechanisms are at work in a particular target environment may
not be necessary to make measurements, it is absolutely essential for the correct and
responsible interpretation of results. In situations where the thermographer is unfa-
miliar with the measurement environment, a knowledgeable facility representative
should accompany the thermographer during the measurements or be available for
consultation. By providing expert information concerning the processes taking
place and the likely sources of temperature differences, this assistance will enable
the thermographer to anticipate thermal behavior and to better understand and in-
terpret the thermographic results.

5.2 Preparation of Equipment for Operation

For point-sensing instruments, preparation for making measurements is a rather
simple matter of checking operation, checking battery status, and executing a sim-
ple calibration check. This preparation does, however, constitute a simple checklist,
and the checklist is a critical element in the successful field operation of thermal
sensing and imaging equipment. In field measurements time consumed, scheduling
of measurements, and the availability of on-site personnel make preparation of the
equipment a crucial factor. A seemingly small oversight in equipment preparation
can often waste considerable money and man-hours.

5.2.1 Calibration and radiation reference sources

Calibration against a known temperature reference is required for all IR measuring
instruments, and this is normally accomplished through the use of radiation refer-
ence sources known as blackbody simulators or blackbody sources. These are tem-
perature-controlled cavities or high-emissivity surfaces that are designed to
simulate a blackbody target at a specific temperature or over a specific temperature
range, with traceability to NIST. Factory calibration and traceability is provided by
the manufacturer. Since most quantitative thermographic instruments measure ra-
diant energy values that are converted to temperature readings by a computer, cali-
bration usually resides in the computer software and is identified with a specific
instrument serial number. If a specific instrument calibration is not available in
software, the computer will usually default to a generic calibration for that class of
instrument.
In addition to a blackbody calibration, the software is usually provided with
correction functions for ambient effects such as atmospheric attenuation as a func-
Using IR Sensing and Imaging Instruments 67

tion of working distance, and for emissivity correction. Default settings for these
values are normally in effect unless the operator chooses to vary them.

5.2.1.1 Checking calibration

In order to check the calibration in detail, a blackbody reference source must be
used. The blackbody must be placed in front of the instrument so that it subtends a
substantial area in the center of the image (much greater than the IFOV for point
sensors and the IFOVmeas for imagers). Where applicable, the correct measure-
ment conditions must be set into the computer (working distance = 10 m, ambient
temperature = 25°C, emissivity = 1, etc.), and the temperature reading compared to
the reference source setting. The spot measurement software diagnostic should be
used over as wide a range of temperatures as possible. If the instrument is not cali-
brated, it may be possible to restore it under certain conditions; refer to the opera-
tor’s handbook. Otherwise, it may be necessary to return it to the factory for
recalibration. Detailed calibrations should be updated at least every six months.
Periodic calibration “spot checks” also should be performed. Ideally, these
should be done before each field measurement mission and can be accomplished by
means of a high-quality radiation thermometer and high-emissivity sample targets.
To perform a spot check, the thermographer should place the target in front of the
instrument as above and set the emissivity the same for both instruments, then mea-
sure the temperature simultaneously with the imager and the radiation thermome-
ter. Spot checks should be run at a few temperatures covering the range of
temperatures anticipated for the specific measurement mission. Since the FOVs
and spectral ranges of the two instruments may not match, exact correlation may
not be possible, but if the errors are repeatable from day to day the procedure will
provide a high degree of confidence in the measurement results.

5.2.1.2 Transfer calibration

Instrument calibrations are run over a broad range of temperatures, with certain
maximum allowable errors occurring at temperatures within this broad range. If ex-
tremely accurate measurements are required within a narrow range of temperatures,
the thermographer may be able to improve on the measurement accuracy by per-
forming a transfer calibration. This requires introducing a radiation reference
source into the total FOV along with the target of interest with the reference set very
close to the temperature range of interest. Using the diagnostic software to measure
the temperature differences between the reference and various points of the target
of interest should provide improved accuracy. Some software packages allow the
thermographer to temporarily transfer the system calibration by placing crosshairs
over the radiation reference source and designating it as the absolute system refer-
ence at whatever value the thermographer assigns it.
68 Chapter 5

5.2.2 Equipment checklist

In preparation for a day of field measurements, the thermographer should use
checklists to ensure that there are no “surprises” on site. A standard checklist should
be prepared to include all items in the thermographic equipment inventory. These
should include instruments, spare lenses, tripods, harnesses, transport cases, carts,
batteries, chargers, liquid or gaseous cryogenic coolant, safety gear, special acces-
sories, film, diskettes, spare fuses, tool kits, data sheets, operator manuals, calibra-
tion data, radiation reference sources, interconnecting cables, accessory cables, and
special fixtures. Well in advance of the scheduled measurements, the thermogra-
pher can highlight all the items that will be required for a particular job. The high-
lighted standard list then becomes the checklist for the job.

5.2.3 Equipment checkout and calibration

The thermographer should perform a quick operation and calibration check to make
certain that the equipment is in working order and in calibration. This can be per-
formed by using an IR radiation reference blackbody source or by a more quick and
simple means such as a two-point check. This approximate test can be performed
by using two known targets such as ice water (0°C) and the palm of the thermogra-
pher’s hand (approximately 35°C).

5.2.4 Batteries
Too many thermographic field measurement missions have been postponed or pre-
maturely terminated because the thermographer ran out of charged batteries. This
can be embarrassing, very costly, and damaging to the thermographic profession.
The “batteries” item on the mission checklist should be understood to mean “fully
charged batteries,” and the thermographer should ensure that there is a comfortable
surplus of battery power available for each field measurement session. The fact that
batteries become discharged more rapidly in cold weather also needs to be consid-
ered when preparing for field measurements.

5.3 Avoiding Common Mistakes in Instrument Operation

Assuming that the instrument complement selected is appropriate to the measure-
ment application, there are a few things to remember to avoid common mistakes in
its use. These include the following:

· Learn and memorize the start-up procedure.

· Learn and memorize the default values.
· Set or use the correct emissivity.
· Make sure the target to be measured is larger than the IFOVmeas (or MFOV) of
the instrument.
Using IR Sensing and Imaging Instruments 69

· Aim the instrument as close to normal (perpendicular) with the target surface as
possible.
· Check for reflections off the target surface.
· Keep sensors or sensing heads as far away as possible from very hot targets.

The following sections review these items one by one.

5.3.1 Start-up procedure

Thermographers who operate several different models of thermographic and ther-
mal sensing equipment should refamiliarize themselves with the start-up procedure
of the equipment selected for a particular field measurement. This allows the
data-gathering process to begin with no unnecessary delays; it saves valuable on-site
time and inspires confidence on the part of facility personnel. A quick review of the
operator’s manual and a short dry run prior to leaving home base are usually all that
is required.

5.3.2 Memorizing the default values

The operator’s manual also provides default values for several important variables
in the measurement such as emissivity, ambient (background) temperature, dis-
tance from sensor to target, temperature scale (°F or °C), lens selection, and relative
humidity. These are the values the instrument’s data processing software automati-
cally uses to compute target temperature unless the thermographer changes these
values to match the actual measurement conditions. Typical default values are 1 m
distance to target, emissivity of 1.0, and background temperature of 25°C. Failure
to correct for these values—if for example the target is known to be 10 m away, is
known to have an effective emissivity of approximately 0.7, and is in an ambient
temperature of 10°C—can result in substantially erroneous results. By memorizing
the default values the thermographer will know when it is necessary to change them
and when time can be saved by using them unchanged without referring to a
look-up menu.

5.3.3 Setting the correct emissivity

Appendix C is a listing of various targets and their approximate generic emissivities.
Emissivities are shown for various temperatures and in several spectral bands. Where
not otherwise indicated, temperatures should be assumed to be 25°C.
These values can be used as a guide when absolute temperature values are not
critical. When measurement accuracy is important, however, it is always better to
directly determine the actual effective emissivity of the surface to be measured us-
ing the actual instrument to be used in the measurement. This is because emissivity
varies with surface characteristics and measurement spectral band, and will often
vary among samples of the same material.
70 Chapter 5

Several methods may be used to quickly estimate target effective emissivity. The
following steps outline one way to determine the emissivity setting needed for a par-
ticular target material using the instrument intended to be used for the measurement:

1. Prepare a sample of the material large enough to contain several spot sizes or
IFOVs of the instrument. A 10 cm ´ 10 cm (4 in. ´ 4 in.) sample is a good
choice.
2. Spray one half of the target sample with flat black (light absorbing) paint, or
cover it with black masking tape or some other substance of known high
emissivity.
3. Heat the sample to a uniform temperature as close as possible to the estimated
temperature at which the actual measurement will be made.
4. Set the instrument emissivity control to the known effective emissivity of the
coating and measure the temperature of the coated area with the instrument.
Note the measurement reading.
5. Immediately point to the uncoated area and adjust the emissivity set until the
reading obtained in step (4) above is repeated. This is the emissivity value that
should be used to measure the temperature of this material with this instrument.

This procedure is illustrated and summarized in Fig. 5.1.

5.3.4 Filling the IFOVmeas for accurate temperature measurements

The thermographer who needs to measure the temperature of a spot on a target
should be certain this spot completely fills the IFOVmeas of the instrument. If it
doesn’t, it is still possible to learn some useful things about the target with the in-
strument, but it is impossible to get an accurate reading of target temperature. The

Figure 5.1 Measuring target effective emissivity.

Using IR Sensing and Imaging Instruments 71

Figure 5.2 Quick calculation for target spot size and IFOV calculation.

quick calculation provided in Fig. 5.2 (Fig. 3.2 repeated) can be used to determine
spot size based on IFOVmeas and actual working distance. For example, if the tar-
get spot size is 5 cm or larger and the calculated spot size is 5 cm, the instrument
should be moved closer to the target or a higher magnification lens should be used.
If these remedies are not possible, some contribution of the target background tem-
perature will appear in the reading. Also, a 30% allowance should be made for er-
rors and instrument imperfections.

5.3.5 Aiming normal to the target surface

The actual emissivity of a target surface is partially due to the surface texture. It
stands to reason, then, that if the thermographer looks at a surface at a skimming
angle where the texture is not visible, the effective emissivity will change greatly
and produce misleading reflections. These can result in “cold” errors as well as
“hot” errors. A safe rule is to view the target at an angle within 30 deg of normal
(perpendicular). If the target emissivity is very high, even a 60-deg angle may be
necessary.

5.3.6 Recognizing and avoiding reflections from external sources

If there is a source of radiant energy in a position to reflect off the target surface and
into the instrument, the thermographer should take steps to avoid misleading re-
sults. The greatest likelihood of errors due to reflections from external sources ex-
ists when:

1. The target emissivity is low,

2. The target is cooler than its surroundings, or
3. The target surface is curved or irregularly shaped.
72 Chapter 5

One way to determine if reflections are present is to move the instrument and point
it at the target from several different directions. If the anomaly (the apparent hot or
cold spot) moves with the thermographer, it is a reflection. Once the reflection is
identified, the thermographer can eliminate the effect of an interfering source by
changing the viewing angle, by blocking the line of sight to the source, or by doing
both. This is illustrated in Fig. 2.10.

5.3.7 Avoiding radiant heat damage to the instrument

Unless specifically selected for continuous operation in close proximity to a very
hot target, the instrument may be damaged by extensive thermal radiation from a
target. A good rule to follow is to not leave the instrument sensing head in a location
where a human hand would suffer discomfort. It is also advisable to avoid aiming
instruments directly at the sun.

5.3.8 Using IR transmitting windows

Infrared transmitting sighting windows, that are also clear in the visible, are used
extensively by the predictive maintenance community and are useful for making
measurements whenever conditions require isolation between the instrument and
the target. During inspections of electrical equipment operating at elevated voltage,
for example, plant regulations frequently prohibit the opening of equipment cabi-
nets. Cabinets can be fitted with approved inspection window assemblies, often by
the cabinet manufacturers, to allow IR inspection of critical equipment without the
need for opening doors.
While inspecting equipment through an IR transmitting window, the transmis-
sion loss through the window as well as the thermal contribution of the window it-
self should be considered. If measurement accuracy is critical, the data furnished
with the window can be used to correct the measurement.

5.4 The Importance of Operator Training

As previously noted, it is a simple task for the novice thermographer to turn on an
IR camera and aim at a target to capture an image. By the same token it is easier than
ever to misinterpret findings. In order to be effective, today’s thermographers must
have a solid grounding in heat transfer and IR basics, as well as a clear understand-
ing of how the instruments operate. Formal operator training is offered by most
equipment manufacturers and several independent training centers.

5.4.1 Training programs and certification

Many organizations that conduct formal in-house self-monitoring thermography
programs conduct training for the thermographers they employ, often providing
Using IR Sensing and Imaging Instruments 73

certification in accordance with their specific needs. One example of this special-
ization is when power generation facilities train their electricians to perform predic-
tive maintenance thermographic inspections on power generation and distribution
systems. Another is when auto manufacturers train engineers to troubleshoot fabri-
cation machinery and plant facilities using thermographic equipment.
For those entities and individuals seeking outside formalization, a set of certifi-
cation guidelines for IR thermographers was developed for the American Society
for Nondestructive Testing (ASNT). The recommended Levels of Qualification for
IR thermographers follow those of the society’s traditional nondestructive evalua-
tion methods. The classroom training is based on the body of knowledge reviewed,
adopted, and updated by ASNT, summarized in ASNT Recommended Practice No.
SNT-TC-1A, and reviewed in “ASNT Level III Study Guide: Infrared and Thermal
Testing Method” (2001). The depths that these areas cover correspond to the levels
of the training. These levels as described in both publications are as follows:

Level I
A Level I infrared thermographer shall be qualified to perform specific IR inspec-
tions in accordance with detailed written instructions and to record the results, and
shall perform inspections under the cognizance of a Level II or Level III. The Level
I shall not independently perform nor evaluate inspection results for accep-
tance or rejection when such inspection results are for the purpose of verifying
compliance to code or regulatory requirements.

Level II
A Level II infrared thermographer shall be qualified to set up and calibrate
equipment, conduct inspections, and to interpret inspection results in accor-
dance with procedure requirements. The individual shall be familiar with the
limitations and scope of the method employed and shall have the ability to ap-
ply techniques over a broad range of applications within the limits of their cer-
tification. The Level II shall be able to organize and report inspection results.
A Level II must have the ability to correctly identify components and parts of
components within the scope of the IR inspection.

Level III
A Level III infrared thermographer is capable of designating a particular in-
spection technique, establishing techniques and procedures, and interpreting
results. The individual shall have sufficient practical background in his/her
area of expertise to develop innovative techniques and to assist in establishing
acceptance criteria where none are otherwise available. The individual shall
have general familiarity with other nondestructive evaluation (NDE) methods
and inspection technologies. The Level III individual shall be qualified to train
and examine Level I and Level II personnel for qualification and certification
as infrared thermographer.
74 Chapter 5

The training requirements for each level of IR thermographer qualification parallel

those for the other traditional NDE methods in that on-the-job training, educational
background, and classroom work all count toward qualification.
There are qualification examinations and annual requalification requirements
in all levels. It is up to the training organization and individual employers to imple-
ment the appropriate recommendations of the training program.
The experience and education recommendations for the three levels are:

Level I
A high school diploma (or equivalent) or 6 months’ experience.

Level II
A 2-year college or technical degree or 18 months’ experience.

Level III
A 4-year technical degree from a college or university or 5 years’ experience.

The training programs offered by manufacturers and training centers are, for
the most part, designed to reflect the ASNT certification guidelines, under
which actual certification is granted by the authority of the organization which
employs the thermographer.

Additional details can be found in SNT-TC-1A and the above referenced study
guide.
 Part II

Instrument Applications
Chapter 6

Introduction to Applications

Applications for IR thermal sensing and thermal imaging (thermography) are found
in virtually every aspect of every industry.
The remaining six chapters will discuss applications that fall generally into the
classifications listed below. However, some classifications overlap, and the solu-
tion to some problems involves multiple approaches that include several classifica-
tions. For example, the detection of moisture-laden sections on flat industrial roofs
is a classic application of passive IR nondestructive material testing. Since the con-
dition occurs on building roofs, it is most frequently included in the “buildings and
infrastructures” category, but when it is part of a facilities maintenance program it
could be considered a condition monitoring application.
The remaining six chapters discuss applications categories as follows:

Chapter 7 Plant Condition Monitoring and Predictive Maintenance

Chapter 8 Buildings and Infrastructure
Chapter 9 Materials Evaluation—Infrared Nondestructive Testing
Chapter 10 Process Monitoring and Control
Chapter 11 Night Vision, Security, and Surveillance
Chapter 12 Life Sciences Thermography

These chapters are offered as brief overviews of each classification. References are
provided where more in-depth information can be gathered on specific applica-
tions.
Tables 6.1 and 6.2 are partial listings of industrial applications of thermal sens-
ing and imaging instruments listed both by discipline and by industry. The overlaps
among disciplines and industries also can be observed.

Table 6.1 Industrial applications of thermal sensing and imaging instruments by in-
dustry.
Industry Applications
Metals Continuous casting, strip annealing, extrusion presses, rolling mills, induc
tion heating, resistance heating, heat treating, electrolytic refining
Glass Tank refractories, glass body temperatures, mold temperatures, bottle ma
chines, float glass, tempering and annealing, fiberglass manufacturing

77
78 Chapter 6

Table 6.1 continued

Industry Applications
Cement Kiln shell, refractory insulation, bridge delamination inspection
Textiles Permanent press heat setting, dye setting, foam lamination, carpet backing
Plastics Vacuum forming, extrusion, film process monitoring and control
Paper Dryer drums, coating ink drying
Chemical Furnace tube temperatures, pipe and vessel corrosion, mixing process
and petroleum monitoring and control
Food Rotary cooker temperatures, continuous IR ovens, mixers, continuous
and confection baking ovens, freeze dry processes
Asphalt paving Road stone dryer, mixing temperature, rolling temperature
Rubber Hot rubber sheets cooling and rolling, tire testing

Table 6.2 Industrial applications of thermal sensing and imaging instruments by

discipline.
Discipline Applications
Design Exhaust stacks, flue pipes, heating units ovens, boilers, furnaces, buildings
(offices, schools, hospitals, plants), process pipes, vessels, steam and water
lines, kilns, cryogenic storage vessels, electrical and electronic circuits and
microcircuits
Workmanship Operational procedures, installation of refractory materials, installation of
foam insulation materials, installation of fiberglass materials (roof insula
tion), replacement of parts and other repairs, roof inspection for moisture
saturation
Component failure Steam traps, underground steam lines, electrical lines and substations, elec
trical and electronic components and modules, insulation foam, fiberglass
and refractory, seals, low and high temperature, doors, ports, windows,
cooling towers, heat exchangers, plumbing lines and systems, motors,
pumps, ventilators, bearings
Chapter 7

Plant Condition Monitoring

and Predictive Maintenance

7.1 Introduction
The use of thermal sensing and imaging in plant condition monitoring and predic-
tive maintenance is probably the most widespread of all current applications. From
periodic spot checks of bearing temperatures on rotating machinery to fully docu-
mented facility-wide programs of predictive maintenance, condition monitoring
accounts for the deployment of more thermographic equipment than any other
commercial use. The basis for these programs is the fact that erratic or deviant ther-
mal behavior of operating equipment is generally a precursor to costly and ineffi-
cient operation and then to failure.
The use of IR thermal viewers and imagers for plant condition monitoring and
field preventive maintenance has grown over the past 25 years to become a univer-
sally accepted adjunct to power facility operation. Thermographic data from hun-
dreds of power line surveys have been collected, and standards have been
developed for the thermal behavior of electrical switchgear and electrical distribu-
tion equipment. Utilities such as the Northeast Utilities Service Company maintain
full-time staffs who perform continuing IR survey work, saving millions of dollars
annually in equipment and downtime. Some years ago the Ontario Hydro Corpora-
tion launched a new kind of thermographic survey van with standard thermal signa-
tures of hundreds of typical disconnects, transformers, power panels, and other
switchgear stored in its data banks. This allows rapid and accurate operator assess-
ment of equipment condition and leads to timely correction of incipient trouble
spots.
Nowhere are the risks of failures and shutdowns more critical than in the nu-
clear power generation industry. Therefore, nuclear power plants have come to be
the facilities that conduct the most comprehensive predictive maintenance pro-
grams using IR thermography. However, the applications within these programs are
typical to almost all plants and facilities.
Condition monitoring problem indications are known as findings because un-
usual heating conditions can be caused by normal events other than failure mecha-
nisms. Findings must therefore be accompanied by other condition information
before they can be validated as incipient problems. Findings fall into three broad
categories: electrical, mechanical, and miscellaneous.

79
80 Chapter 7

7.2 Electrical Findings

Electrical applications represent the primary use of IR thermography in facilities
and utilities. They also represent the most straightforward application of the equip-
ment. The most common electrical findings are caused by high electrical resistance,
short circuits, open circuits, inductive currents, and energized grounds.

7.2.1 High electrical resistance

High electrical resistance is the most common cause of thermal hot spots in electri-
cal equipment and power lines. Ohm’s law states that power dissipated in an operat-
ing element, and the resultant heating, is equal to the square of the current
multiplied by the resistance: P = I2R. When the line current is relatively constant
and resistance is higher than it should be, additional power is dissipated and a ther-
mal anomaly occurs. This is always costly and frequently dangerous. The cost fac-
tor is manifold. First, the connection dissipates valuable watts in the form of
unwanted heat instead of useful work. Second, the increased resistance causes an
additional voltage drop and results in increased current to the load with no increase
in work. Third, the elevation in temperature causes accelerated aging, which neces-
sitates earlier equipment replacement. Typical examples of resistive heating in-
clude loose connections, corroded connections, missing or broken conductor
strands, and undersized conductors. Figure 7.1 is an example of excessive heating
caused by high resistance at a clip connection due to deterioration of the connec-
tion. The upper end of the center clip appears to be more than 50°F warmer than the
corresponding connections on the other two phases.
In power lines and switchyards, hot connections due to deterioration are the
most common findings that are considered incipient failures. Figure 7.2 is an exam-
ple of overheating in a switchyard due to a faulty contact. The elevated contact re-
sistance results in a temperature rise of greater than 10°C.
Figure 7.3 is an example of a disastrous electrical failure that might have been
avoided with a more aggressive condition monitoring program. Here a leaking iso-
lator (arrow) that appears slightly overheated in the upper thermogram fails disas-
trously 30 seconds later, as shown in the lower thermogram.
Figure 7.4 is an example of the value of thermal image fusion in predictive
maintenance applications. Here the heated connections are easily identified by fus-
ing the thermal image and the visible image of an electrical panel.

7.2.2 Short circuits

When power line short circuits occur, they usually are of extremely brief duration
and have immediate and disastrous results. Short circuits within an operating com-
ponent, however, can be detected and diagnosed using thermographic equipment;
the shorted section will cause excessive current to flow, with resultant heating. One
example of this would be shorted sections of a current transformer winding. The
Plant Condition Monitoring and Predictive Maintenance 81

Figure 7.1 Excessive heating of a connecting clip due to deterioration (courtesy of

FLIR Systems, Inc.).

Figure 7.2 Overheating at a switchyard disconnect due to high contact resistance

(courtesy of Raytheon/Amber).

finding here would be that the transformer would appear hotter than normal and/or
hotter than other similar devices. Similar problems can occur within rotating equip-
ment such as motors and generators and within power supplies.
82 Chapter 7

Figure 7.3 Disastrous failure of leaking isolator (courtesy of FLIR Systems, Inc.).

7.2.3 Open circuits

Open circuits are often overlooked by inexperienced thermographers as indications
of potential problems because they do not generally show up as hot spots. An oper-
ating element running cooler than normal may indicate that the element is
open-circuited and inoperative. A common problem with inverters, for example, is
Plant Condition Monitoring and Predictive Maintenance 83

Figure 7.4 Fusion of a visible and thermal image of a complex electrical panel (cour-
tesy of Fluke Corp.).

“blown” (open) capacitors. The failed capacitors will appear cooler than other simi-
lar capacitors within the inverter. On power supplies, resistors or integrated circuit
chips that are open and inoperative will also appear colder than normal, although
the malfunction may cause excessive heating elsewhere in the operating element.

7.2.4 Inductive currents

Inductive currents can cause excessive heating within ferrous components or ele-
ments that are within the magnetic field of large equipment such as the main gener-
ator in a power plant. Hot spots can appear in seemingly unlikely locations such as
motor frames and structural elements. Several examples have been documented
where steel bolts have been inappropriately used to replace nonferrous bolts in
framework supporting large rotating machinery. Hot spots caused by inductive
heating do not always lead to danger or failure, but these findings should be well
documented by the conscientious thermographer.

7.2.5 Energized grounds

Energized grounds are commonly occurring phenomena in plants and facilities, and
are in many cases considered “life safety” situations. Since an energized ground
connection is usually extremely hot, it is seldom difficult to identify it thermo-
graphically. The problem is tracing the cause, which may be elusive. The cause may
be partial insulation breakdown in an operating element. The ground connection
may also be carrying induced currents due to a breakdown on an element in close
proximity. Most often the diagnosis requires considerable input from knowledge-
able facilities personnel.
84 Chapter 7

7.2.6 Condition guidelines

Thermographers who start new programs frequently ask the question, “How much
temperature deviation from normal constitutes a problem condition?” Because
there are so many factors, including ambient variations, that can influence tempera-
ture, there is no simple answer to the question. With this caution in mind, however,
it is reasonable to set forth guidelines to assess the severity of findings based on
common sense and experience. The development of guidelines began in the electri-
cal industry, and today most facilities have “rule-of-thumb” systems whereby they
classify the potential severity of a finding based on temperature rise and known
load conditions. An example of classification guidelines is provided in Table 7.1.
The guidelines listed are based on 50% of rated load. The method for adjusting the
guidelines as load conditions vary is also shown. Please note that these guidelines
are based on one company’s knowledge and experience. No single method is uni-
versally accepted.

Joules law: P = I2R. Use this to proportion the temperature rise to 50% of the
load.

Example: At 20% of load, an 8°C rise is seen. To proportion it to 50% of load,

multiply by the square of the load ratio as follows:

(50/20)2 = 6.25.
6.25 ´ 8°C = 50°C rise.

Table 7.2 summarizes another set of guidelines used in the electrical industry for
compensating for the cooling effects of wind loading on outdoor electrical
thermographic measurements. The table shows adjustment factors for wind speeds
up to 9 m/s (18 knots). Thermographic measurements are not recommended at wind
speeds greater than 9 m/s.

Table 7.1 Classification of electrical faults.

Temperature Rise
Class Description
(based on 50% max load)
I Greater than 0.5°C First stage of overheating. Should be kept under
control and repaired at the next scheduled main
tenance.
II 5 to 30°C Developed overheating. Repair at the first oppor
tune moment with due consideration to the load
ing environment.
III Greater than 30°C Acute overheating. Repair at once but with due
consideration to the load.
Plant Condition Monitoring and Predictive Maintenance 85

Table 7.2 Compensating for wind effects (courtesy of FLIR Systems, Inc.).

Wind Speed (m/s) Correction Factor

1 (or less) 1.00
2 1.36
3 1.64
4 1.86
5 2.06
6 2.23
7 2.40
8 2.50
9 (or more) measurements not recommended

Please note that these guidelines represent one company’s attempt to approximate
wind effects in the absence of a more formal protocol. They do not take into account
such variables as gusts and wind direction.

1 m/s = 2 knots = 2.2369 mph.

Example:
An excess temperature rise on a component is measured to be 5°C at a wind veloc-
ity of 8m/s. The actual excess temperature is calculated to be:

5 ´ 2.54 = 12.7°C.

7.3 Mechanical Findings

Mechanical findings that most frequently occur in plants and facilities are classified
in one of four categories: building defects, friction, valve or pipe malfunction
(blockage/leakage), and insulation defects within the plant. Building defects appli-
cations, including building insulation, are discussed in Chapter 8. The other three
categories are discussed below.

7.3.1 Friction
Identification of problems due to excessive friction and its resultant heating are the
most common types of mechanical applications for IR thermal sensing, and most of
these occur in rotating machinery. Problems encountered include worn, contami-
nated, or poorly lubricated bearings and couplings and misaligned shafts. Typical
findings occur in pump motors such as those shown in Fig. 7.5, where the deteriora-
tion of lubricant in the motor to the right results in temperature rises at the location
86 Chapter 7

Figure 7.5 Overheated pump motor at right caused by lubricant deterioration

(courtesy of General Motors Powertrain).

of the bearing. A misaligned shaft will result in unequal loading and cause heat gen-
eration at the point of highest mechanical resistance.

7.3.2 Valve or pipe blockage/leakage

Thermographic location of valve or pipe leakage may be simple or involved, de-
pending on a number of conditions. Detecting the leak is usually simple if the valve
or pipe section is not covered with insulating material, and if the temperature of the
fluid conducted by the valve or pipe section is sufficiently hotter or cooler than am-
bient. For example, when a hot fluid passes through a closed valve, the temperature
becomes elevated on the far side of the valve and can be observed thermogra-
phically. Steam traps are special valves that automatically cycle open and closed to
remove condensate from sections of steam process lines. If the thermographer has
prior knowledge of their appropriate operation, steam traps can be observed
thermographically to determine if they are operating properly.
Figure 7.6 shows a thermogram (above) and photo (below) of three steam traps.
In normal operation of this type of trap, the outlet (top) warms when the trap opens
and discharges, and cools when the trap closes and begins to refill. The malfunc-
tioning (leaking) trap on the left side exhibits no temperature differential between
the inlet and the outlet.
Blockage of a fluid transfer line can be simple to detect thermographically if
the fluid temperature is sufficiently hotter or cooler than ambient. If not, there are
more subtle approaches that have had documented success. The application of uni-
form transient heat, for example, will often result in temperature differentials at the
blockage site because of the difference in thermal capacity between the fluid (in liq-
uid form) and the solid blockage.
Plant Condition Monitoring and Predictive Maintenance 87

Figure 7.6 Abnormally functioning steam trap shown on the left side (courtesy of FLIR
Systems, Inc.).

7.3.3 Insulation within the plant or facility

Much of the equipment, conduit, and piping within a facility that contains or car-
ries heated or cooled fluid is customarily insulated to conserve thermal energy
and for safety reasons. Thermography is routinely used to test for uniformity and
integrity of thermal insulation. Observed thermal differentials can be used to de-
tect the effects of missing insulation, thinning or degraded insulation, and wet in-
sulation. A discussion of thermographic building insulation inspection is included
in Chapter 8.

7.4 Miscellaneous Applications

Miscellaneous applications – those that don’t exactly fit into the electrical or me-
chanical categories – are numerous and sometimes unique to one industry. The fol-
lowing applications are usually encountered in the power generation industry, but
also have counterparts in other industries.
88 Chapter 7

7.4.1 Rebar location

One of the first uses to which thermographic equipment was applied was in the
rapid location of rebars (steel reinforcing bars) in reinforced concrete walls so that
openings could be cut without damaging the reinforcement. The technique used
was based on induction heating. A current-carrying induction coil was placed
against the wall surface so that the steel rebars were heated and could be observed
with the IR imaging system. In this and similar applications, parallax effects can
make the hidden ferrous elements seem to appear in an offset location; care should
be taken to aim the sensor head perpendicular to the wall to avoid parallax.

7.4.2 Condenser air in-leakage

One of the more cost-sensitive surveys that has been developed is the periodic inspec-
tion of condensers for air in-leakage. The condenser is the component that changes
the steam into water after it has done work in the turbine. This is part of the system
that removes heat from the water to produce power. During the process a strong vac-
uum results and the inside of the condenser is at about 0.7 psia, 5% of normal atmo-
sphere (14.7 psia). Air leaking into the condenser below the water level adds dissolved
oxygen to the water and promotes corrosion, which in turn leads to early failures,
costly parts replacement, and excessive downtime. Although an individual leak may
be small, numerous leaks can inject unacceptable quantities of dissolved oxygen into
the water. Excessive air in-leakage above the water level may significantly reduce the
power potential of the turbine by blocking the steam flow.
In-leaking manifests itself as subtle cooling around valve stems, valve bonnets,
flanges, instrument connections, and manways that can be detected by scanning the
outside of the system with thermal imaging equipment. Since the cooling is fre-
quently less than 1°C, the inspection must be done with great care. This type of sur-
vey is performed quarterly at most nuclear facilities.

7.4.3 Containment spray ring headers

The containment spray ring header in a nuclear power generating facility is a safety
system that helps mitigate excessive heating in the reactor area by spraying endo-
thermic (heat-absorbing) sodium hydroxide (NaOH) into the area if necessary. The
header contains many nozzles that may periodically become blocked. Thermo-
graphic inspection to verify unblocked nozzles involves pumping heated air into
the header and observing the thermal patterns caused by the air leaving the nozzles
for consistency and temperature. Most frequently, because of the small nozzle size
and the required safe distance from the imager, the thermographer finds it necessary
to use a high-resolution telephoto IR lens.

7.4.4 Hydrogen igniters

Containment hydrogen igniters are safety devices that mitigate the buildup of excess
hydrogen in the reactor building by slowly burning it off in the event of a nuclear ac-
Plant Condition Monitoring and Predictive Maintenance 89

cident. The use of IR thermography for inspecting containment hydrogen igniters is

relatively recent. It allows the temperature of these highly inaccessible devices to be
measured remotely and without contact, but again, a telephoto IR lens is required.

7.4.5 Effluent thermal plumes

The thermal discharge of the power plant, and its expected environmental impact
on waterways, is routinely evaluated by thermographically inspecting the effluent
plume from an airborne platform such as a helicopter. The thermal plume is easily
observed from the air – the hottest spots on the water surface indicate the tempera-
ture and direction of the outfall.

7.4.6 Gas leak detection

Thermal imaging is the only reliable remote noncontact method for gas leak detec-
tion. This approach exploits the IR spectral absorption characteristics of invisible
gases. First, the spectral absorption band of the gas, or class of gases, necessary to de-
tect is determined. Then the instrument spectral response is selected to match that ab-
sorption band, usually by means of selectable or interchangeable interference filters.
The plume of leaking gas will then appear as an opaque, cool cloud (usually black)
against a warmer target background on the thermal image as shown in Fig. 7.7.

7.4.7 Seal failures

The failure of seals due to wear and fatigue can cause loss of energy and lead to di-
sastrous failure. Figure 7.8 is a photo (left) and thermogram (right) of a leaking seal
in a joint between a gas turbine and a steam boiler in a heat recovery steam genera-
tor (HRSG) system showing temperature rises of more than 300°C.

Figure 7.7 Gas leak in valve appears as a black cloud on the thermogram (courtesy
of FLIR Systems, Inc.).
90 Chapter 7

Figure 7.8 Leaking seal in a joint between a gas turbine and a steam boiler (courtesy
of SA Termografia Infrarroja).
Chapter 8

Buildings and Infrastructure

8.1 Introduction
Applying IR radiation measurements to the detection of energy losses in structures
was one of the first commercial uses for IR sensing and imaging. Generally speak-
ing it is a rather indirect use of the measurement tools available. Point sensors and
imagers can provide excellent information concerning the radiation temperature
and temperature distribution over building surfaces. The relationship between sur-
face temperature and energy loss, however, depends on a number of physical and
environmental factors as well as the insulating characteristics of the structural ma-
terials and the integrity of the structural section.
Driven by the energy crisis of the 1970s, which is still very much an issue,
communities and government agencies instituted IR aerial scans by adapting mil-
itary aerial thermal mappers. The purpose of these scans was to provide commu-
nities, residents, and commercial taxpayers with information concerning the heat
loss characteristics of their buildings. Although only losses through the roofs
were detected, unheated buildings did not register at all, and numerous environ-
mental factors clouded the results, these early programs raised community con-
sciousness and identified a new tool for energy conservation. They were also a
major driving force in the development of commercially available IR sensing and
imaging equipment.
Nationally sponsored and funded building retrofit and weatherization pro-
grams were put into effect in European countries (Sweden was the first), in Canada,
and in the U.S. Infrared thermal sensing and imaging equipment, now developed
specifically for the commercial market, was used extensively in these pro-
grams—first to assess the retrofit requirements, and subsequently to check the ef-
fectiveness of the work. These were, for the most part, ground-based instruments
that provided more comprehensive information about the structures and also pro-
vided “ground truth” baselines for the aerial scans. Although priorities have
changed, programs of this kind continue. In addition, although the initial thrust of
these applications was aimed at energy conservation, it soon became apparent that
very many other aspects of buildings and structures could be evaluated using IR
sensing and imaging equipment.

91
92 Chapter 8

8.2 Measuring Insulating Properties

As discussed in Chapter 2, the conductive heat flow through a laminar structure is re-
lated to both the temperature difference from one side of the structure to the other and
the aggregate thermal resistance of the materials encountered. Expressed more sim-
ply, the higher the thermal resistance of the materials, the less heat will flow. There-
fore, measuring the temperature on the outside of a structure and knowing the thick-
ness and the inside temperature permits the determination of thermal resistance
(insulating properties). A thorough, though simplified, explanation of heat flow
through structures can be found in the paper, “Fundamentals of heat transfer through
structures” (R. Madding, ThermoSense II, Proceedings, American Society of Photo-
grammetry, 1979), which serves as an excellent primer to this applications category.
As Madding points out, however, the measurement of conductive heat flow for insu-
lation assessment is only one factor in practical heat loss determination.

8.3 Considering the Total Structure

Madding goes on to explain some of the other factors such as air infiltration and
exfiltration, chimney effects, and thermal short circuits or bypasses which, in many
cases, can be serious enough to completely negate the benefits of a retrofit insula-
tion program.
Over the years thermographers have learned to consider the total structure
when evaluating the results of thermographic surveys and have learned to recog-
nize and isolate thermal patterns typically associated with air flow as well as those
caused by insulation deficiencies. An example of the distinct pattern difference is
illustrated in Figs. 8.1 and 8.2. Figure 8.1 illustrates the effects of air exfiltration on
the thermogram of an exterior wall, while Fig. 8.2 shows the distinct patterns cau-

Figure 8.1 Thermogram of a building showing the effects of air exfiltration (courtesy
of FLIR Systems, Inc.).
Buildings and Infrastructure 93

Figure 8.2 Thermogram of a building showing the effects of insulation deficiencies

(courtesy of FLIR Systems, Inc.).

sed by insulation deficiencies. Although temperature reference scales are shown,

absolute temperatures are not as significant as differentials and thermal patterns.
It should be noted that most structural applications are more concerned with
qualitative features, such as thermal patterns and thermal anomalies, than they are
with quantitative temperature measurements. The only reference to temperature
measurements might be the stipulation that, for most building inspections to be
valid, “there should be a minimum of 10°C between the inside and outside surface
temperatures of the building for at least three hours prior to the survey” (guideline
ANSI/ASHRAE 101-1981 in “Application of Infrared Sensing Devices to the As-
sessment of Building Heat Loss Characteristics,” American Society of Heating,
Refrigerating, and Air-Conditioning Engineers).

8.4 Industrial Roof Moisture Detection

Thermographic equipment has been used extensively for the detection of saturated
sections of flat industrial roofs since the 1970s. As in most buildings and structures
applications, these surveys are concerned with detection and identification of ther-
mal patterns rather than quantitative measurements. These patterns are indications
of subsurface moisture, and there are two approaches to making these measure-
ments. One depends on solar heating (insolation). The other approach, taken when
there has not been adequate insolation, requires that there be a minimum of a 10°C
difference between interior and exterior surface temperature for at least 24 hours
prior to the survey. Both are conducted at night with all surfaces clean and dry and
in the absence of high winds (no greater than 15 mph).
When there has been adequate solar heating of the roof during the day prior to
the survey, thermal energy is stored in the roof. The saturated sections have higher
thermal capacity than the dry sections and therefore store more heat. At night, the
94 Chapter 8

roof radiates thermal energy to the cold sky. At some time during the night, the dry
sections have expended all their stored heat but the saturated sections are still warm
due to the high thermal capacitance of the water. When this occurs, the thermogra-
pher can easily locate and identify the saturated sections. This approach is rela-
tively free of thermal artifacts due to vent pipes, exhaust fans, etc., particularly if
there is no temperature difference between the building’s interior and exterior.
The second approach is based on heat loss rather than solar gain. The saturated
roof sections are better heat conductors (poorer insulators) than the dry sections.
The temperature difference between the interior and exterior will cause heat to flow
more through the wet sections than the dry sections. Consequently, warmer areas on
the exterior surface indicate water saturation. Of course, since there is a tempera-
ture differential between the interior and exterior, this approach is more subject to
artifacts caused by air flow and thermal conduction through the roof. The appear-
ance of the thermograms is otherwise quite similar.
Figure 8.3 illustrates the detection of rampant roof moisture on a flat roof based
on solar heating. The saturated areas (lower left) appear to be more than 1°C
warmer than the unsaturated areas, and have a distinct shape that follows the satura-
tion patterns. The thermogram shown was taken from the roof, but both aerial and
rooftop-based scanning can provide effective surveys, each with advantages and
disadvantages. The aerial survey can cover many structures in a few minutes and
images from a more perpendicular vantage point, but it provides more general in-
formation, often missing small anomalies. The rooftop-based survey takes several
hours per structure but provides impressive detail. For validity, both should be ac-
companied by supporting intrusive evidence such as roof core samples.
Figure 8.4 illustrates the effects of heat loss through a peaked roof with a uni-
form inside temperature higher than the outside temperature. The thermal patterns
observed are dominated by differences in building insulation and no evidence of
water saturation is present.
In 1990, the ASTM released the Standard Practice for the Location of Wet In-
sulation in Roofing Systems Using Infrared Imaging (ASTM C1153-90), which
outlines the minimum criteria for an acceptable IR roof moisture survey and clearly
stipulates the requirement for both dry and wet core samples. It also defines the
minimum performance specifications of thermal sensing and imaging equipment
used to perform thermographic surveys.

8.5 Subsurface Leaks and Anomalies

Figure 8.5 illustrates the use of thermography to study subsurface thermal charac-
teristics. The location of the subsurface heating elements and the radiant heating
pattern of a parquet floor (left) are revealed in the thermogram (right) with no ap-
parent leaks. A leak would show up as a thermal anomaly.
Thermography is used frequently on floors and ice skating rinks to avoid dam-
age to heating/cooling elements during repairs and modifications.
Buildings and Infrastructure 95

Figure 8.3 Thermogram of a roof with moisture saturation (courtesy of Infrared Ther-
mal Imaging Corp.).

Figure 8.4 Roof thermogram with heated interior showing insulation differences and
no water saturation (courtesy of Infrared Thermal Imaging Corp.).

Figure 8.5 Photo (left) and thermogram (right) of a radiantly heated floor (courtesy
of SI Termografia Infrarroja).
96 Chapter 8

Figure 8.6 Insulation void on visibly featureless wall is pinpointed using thermal image
fusion (courtesy of Fluke Corp.).

8.6 Thermal Image Fusion Benefit

One benefit of thermal image fusion in building diagnostics is the ability to pinpoint
the location of thermal anomalies on visibly featureless targets. One such example
is illustrated in Fig. 8.6. Blending the visible and thermal images of an interior wall
surface allows the thermographer to locate an insulation void (blue area) with preci-
sion.
Also shown is the picture-in-picture feature available on some of the new IR
cameras. The left-hand image is IR only, the center image is visible only, and the
right-hand image is a 50% blend of the two images. A visible mark on the floor is
used as an orientation point.

8.7 Thermographic Inspection of Our Aging Infrastructure

The techniques described in the preceding sections of this chapter are applicable, to
a large extent, to insulated and laminar structures throughout the economy. Within
the past decade considerable thermographic inspection work has been done on in-
dustrial structures, bridges, and roadways aimed at the detection and evaluation of
cracks, voids, delaminations, and other signs of aging. Because most of the pub-
lished work regarding these applications was performed using external sources of
heat, they fall into the category of active thermography applications, which are dis-
cussed in Chapter 9, Materials Testing.
Chapter 9

Materials Testing

9.1 Materials Testing—IR Nondestructive Testing

Infrared thermal imaging (thermographic) systems measure the self-emitted radiant
energy from the surface of a target remotely and without contact, and produce ther-
mal images in monochrome or color that characterize the distribution of surface
temperature. Using the thermal distribution on the surface of a product sample as a
measure of acceptability is only valid when thermal signatures of acceptable prod-
ucts have been studied, when standard acceptable patterns have been determined,
and when maximum allowable deviations from these standards have been estab-
lished.
A passive measurement approach is taken to establish standard patterns when
products are being evaluated during normal operation or manufacture, and when
the process being monitored produces, or can be made to produce, the desired char-
acteristic thermal pattern on the product surface. The building thermograms shown
in Figs. 8.1 through 8.6 are examples of passive nondestructive testing when the
heat flow from the inside of the structures to the outside is part of normal operation.
When this cannot be made to occur, or when the products or materials are to be eval-
uated after manufacture, an active, or thermal injection, approach is necessary.
Thermal injection can be steady-state or transient (pulsed).
Infrared nondestructive testing (IRNDT) of laminar materials is based on two
facts: (1) that a good structural continuity invariably provides good thermal conti-
nuity, and (2) that voids, unbonds, and foreign matter affect the flow of thermal en-
ergy across (normal to) the laminar layers. The thermal injection approach consists
of the following requirements:

· Generation of a controlled flow of thermal energy across the laminar structure

of the sample material under test,
· Thermographic monitoring of one or sometimes both of the surfaces of the
sample, and
· A search for the anomalies in the thermal patterns so produced that they indi-
cate a defect in accordance with established accept-reject criteria.

The equipment necessary to perform IRNDT must therefore include not only
thermographic imaging instrumentation, but also the means to handle the test sam-
ples and to generate and control the injection of thermal energy into the samples.

97
98 Chapter 9

Mechanisms presently and previously used to generate and inject thermal en-
ergy into test samples include hot and cold air blowers, liquid immersion baths, heat
lamps, capacitor-driven flash lamps, controlled refrigerants, electric current,
scanned lasers, and induction heating. The aim has usually been to maximize the
normal thermal flow, minimize the lateral thermal flow along the material surface,
cause no permanent damage to the test samples, minimize and carefully meter the
test time, and generate as uniform a thermal pattern as possible across the surface of
the test sample. Since the energy source is usually a point, it is often difficult to gen-
erate a uniform thermal pattern on the sample surface. In recent years, however, the
addition of personal computers to store, recover, manipulate, and analyze data ob-
tained by thermographic systems has greatly expanded the power of thermography.
One of the more important software capabilities available today is that of key-
board-controlled image manipulation and subtraction. This image subtraction ca-
pability can be quite effective in compensating for limitations in heating pattern
uniformity.
The personal computer with appropriate diagnostic software, then, becomes
the third element of the modern thermographic nondestructive testing system.
Commercially available thermographic software packages include other features
that are not yet fully exploited but extremely promising for nondestructive materi-
als testing. Examples of these are area comparison and analysis capabilities for
comparing patterns in one segment of a sample to those on other segments. The new
software also facilitates the precision timing and recording of test sequences so that
they can be repeated with consistency, and should also be useful in identifying ther-
mal patterns that are frequently associated with specific kinds of flaws. An example
of this pattern recognition capability is in distinguishing between a surface
emissivity variation and a true thermal difference. An emissivity artifact will gener-
ally have a sharply defined boundary, and a true thermal difference will usually ex-
hibit a more gradual change and less sharply defined boundaries. The computer can
be used to help classify these anomalies.
The materials that are ideally suited for IRNDT evaluation are laminar in struc-
ture and have high and uniform surface emissivity. Most materials currently being
successfully evaluated by IRNDT are composed of layers of metals, plastics, com-
posites, or combinations of all three. The surfaces may be metal or plastic and the
core structure may be solid, amorphous, or geometrically configured. The geomet-
ric structure may be the classic honeycomb pattern or any of several new and inno-
vative patterns presently being considered by various airframe manufacturers. The
surfaces of the materials are usually uniform in appearance and finish, although
surface scratches and irregularities are frequently present.
Figure 9.1 illustrates a typical IRNDT configuration using the steady-state ac-
tive (heat injection) method. Continuous uniform heat is applied to one surface of a
laminar test sample and an IR scanner views the opposite surface. When all of the
variables listed are optimized, two types of defects are detectable. A metal occlu-
sion within the structure has a higher thermal conductivity than the ply material and
results in a warm spot on the scanned surface. A void within the structure has a
Materials Testing 99

Figure 9.1 Example of steady-state, active (heat injection) IRNDT for occlusion and
void detection.

lower thermal conductivity than the ply material and results in a cool spot on the
scanned surface.
The two-sided configuration is usually the simplest to implement. In some
applications, however, depending on the predicted heat flow characteristics of the
materials, it may be more desirable to use a one-sided configuration where the
heat source and the imager are both aimed at the same surface. When both sur-
faces are not readily accessible, of course, the one-sided configuration is the only
alternative.

9.2 Failure Modes and Establishment of Acceptance Criteria

Typical failure modes of these materials are caused by voids between layers,
unbonds between layers, impurities or foreign material in the laminar interfaces,
and significant irregularities (damage) to the geometric core structure. Criteria for
acceptability of each part to be evaluated must be established in terms of minimum
size of void to be detected, minimum area of disbond that can be said to constitute a
defect, and any other void or disbond characteristic that is deemed significant. To
start the program, then, it becomes necessary to use samples of known acceptable
and known defective parts. Ideally, the defective samples furnished should include
known defects of each classification and the minimum sizes required to be detected
and identified. When this isn’t possible it becomes necessary to synthesize flaws in
the samples to simulate the minimum defects.

9.3 Selecting the Right IR Imaging System

Once the basis for acceptance and rejection of each of the samples is established,
then the performance characteristics for the thermographic equipment can be deter-
mined. To be effective, thermographic equipment should offer resolution, sensitiv-
100 Chapter 9

ity, and versatility somewhat beyond that necessary to detect and identify the
expected defects. The most critical of the imager performance characteristics are:
minimum resolvable temperature—the smallest change in blackbody equivalent
temperature that can be clearly detected by the scanning system; spatial resolu-
tion—the instantaneous minimum spot size at the plane of the target in which a tem-
perature change can be detected; and scan speed—the frequency with which
complete thermographic target information is repeated (updated) by the scanner.
The selection of an imager is usually based on a thermal sensitivity (MRT) and spa-
tial resolution to easily detect the rejectable anomalies, and a scan speed adequate
for ease and convenience of operation. Scan speed can be critical when thermal
anomalies are expected to be transient. In testing aluminum–to–aluminum bonds,
for example, very fast capture speeds are necessary.
The effective surface emissivities may become a factor when the parts are made
of unfinished or polished metal. As emissivity decreases, reflectivity increases and
the scanner may detect ambient background reflections and reflections of other local
unrelated sources of thermal energy. The problem of limiting or baffling these un-
wanted reflections off low-emissivity surfaces is no different than making direct ther-
mal IR temperature measurements, but with the advantage that anomalies or
differences are sought rather than absolute temperature measurements. Since patterns
are more significant than absolute temperature measurements, apparent temperature
variations caused by differences in effective emissivity are not of prime importance.
Figure 9.2 illustrates the detection of cable insulation defects using the con-
trolled flow of electrical current through the conductors as an active heat source.
The heat generated in the conductors as a result of current flow, which can be ex-
pressed as P = I2R, flows radially outward to the cable or harness surface, resulting
in an even or isothermal temperature distribution over the surface except where in-
sulation defects are present. Voids, bubbles, and cracks in the insulation produce
anomalies in the thermal patterns that indicate defects in accordance with estab-
lished accept-reject criteria.

Figure 9.2 Three-view thermogram of a cable section with electrical current used as
the active heat source (courtesy of Materials Technologies Corp.).
Materials Testing 101

In the test shown, a mirror configuration is used to produce three simultaneous

views of the test sample, with each view covering 1/3 of the periphery. A surface
chafe can be seen at the left end, and cracks can be seen at the left and center.
For in-situ cable assemblies, it is often undesirable to inject current or to access
cable terminations. In those instances external heat injection is necessary, which
adds to the complexity of fixturing and controlling the thermal energy source.
One of the earliest, and probably the most successful, IRNDT application has
been in detecting flaws in aircraft structures. In the 1970s IRNDT was used to pro-
duce the C5-A cargo transport. This application continues to be important, and most
major airframe manufacturers have ongoing in-house IRNDT programs. In many
of the more recent applications, target test configurations do not allow two-sided
access; the solution is often to use pulsed energy sources or to both heat and monitor
the accessible surface.

9.4 Pulsed Heat Injection Applications

Since the early 1990s, innovative approaches to heat injection such as thermal pulse
and thermal wave propagation have improved the capability for detecting and as-
sessing small and buried flaws. These improvements, coupled with improvements
in computer enhancement methods for isolating and analyzing thermographic pat-
terns, have had an important effect on image understanding and flaw recognition.
With few exceptions, these new approaches involve the time-gating of thermal
image sequences following the application of heat, usually a pulse, in order to char-
acterize defects at various depths below the target surface. The term time-resolved
infrared radiometry (TRIR) is generally used to describe the technique, as illus-
trated graphically in Fig. 9.3.

Figure 9.3 Basis for time-resolved IR radiometry (TRIR) (courtesy of Johns Hopkins Uni-
versity).
102 Chapter 9

After an initial heating pulse is applied to the front surface, heat propagates into
the material and the surface begins to cool uniformly. If a thermal obstruction such
as a disbond or void is encountered, the heat propagation is impeded, causing a
warm anomaly on the cooling surface to appear directly above the void. All other
factors being equal, the timing of the appearance of the warm anomaly on the sur-
face can then be related to the depth of the thermal discontinuities encoun-
tered—the anomaly from a shallow defect will appear sooner and that from a
deeper defect will appear later. Consequently, a time-dependent image search can
yield the optimum image of flaws at any given depth. The illustration shows how
successive thermograms can reveal different depth-related information.
Many publications use different terms to describe the same or similar tech-
niques, which may be confusing to the reader. Much of the work in this area was pi-
oneered by scientists at Wayne State University (Detroit, Michigan), Johns
Hopkins University (Baltimore, Maryland), Universite Laval (Quebec, Canada),
and other institutions. In its earliest applications, in 1978, the pulse injection tech-
nique was limited to single- point measurement and was called photoacoustic mi-
croscopy because although heat does not generally flow in thermal waves, the flow
of heat in the pulsed samples simulated the propagation and reflection of sound
waves. The availability of high-speed imagers dramatically increased the speed,
and hence the usefulness and popularity, of the technique. The pulsed approach to
TRIR thermography has been called thermal wave imaging, pulsed thermography,
and time-gated thermography, among others.
In general, a typical pulsed thermography system consists of the following ele-
ments:

· A pulsed heat source (flash lamps, pulsed laser, time-gated microwave)

· An IR camera
· Image processing hardware (electronic switching and gating)
· Image processing software
· A personal computer

This basic configuration is illustrated in Fig. 9.4.

Figure 9.5 illustrates several results of thermal wave injection and com-
puter–enhanced image analyses. These are furnished by Thermal Wave Imaging,
Inc. Figure 9.5(a) shows a buried adhesive disbond between the 11-ply skin and a
rudder spar on an F15 aircraft rudder assembly. Figure 9.5(b) is a 3D presentation of
an aircraft lap seam in which severely corroded areas appear as red peaks surround-
ing the fasteners (blue). Figure 9.5(c) is a comparison of a good spot weld (left) and
a bad one (right). Figure 9.5(d) illustrates several flaws under a boron epoxy patch
(clockwise from top right): hydraulic fluid infiltration, skin-to-core disbond, miss-
ing core, Teflon insert, and water infiltration (center). Figure 9.5(e) shows impact
damage to a graphite epoxy panel. Figure 9.5(f) is an E2-C2 propeller with a diago-
nal crack in the foam under the fiberglass skin.
Materials Testing 103

Figure 9.4 Configuration for pulsed thermography (courtesy of Thermal Wave Im-
aging, Inc.).

9.4.1 New signal-based technique simplifies image interpretation

In 2000 a newly-developed technique known as thermographic signal recon-
struction (TSR) was introduced that aimed to improve image quality and simplify
operator decision making. TSR is based on signal processing rather than image
processing and is made possible by the speed and power of today’s computers.
TSR data processing reduces hundreds of image data points to an equation with a
few coefficients. Temporal noise is reduced by means of a low-pass filter, and the
images are reconstructed mathematically with reduced noise and improved clar-
ity. The process is automated so that decision making (defect or no defect, depth
of defect, etc.) can be objective rather than based on the operator’s visual interpre-
tation.
Figure 9.6 illustrates the effectiveness of TSR. The left-hand image is the raw
pulsed-thermography image of a graphite epoxy test sample. The center image is a
mathematically processed reconstructed image, and the right-hand image is a com-
puter-generated color-coded depth map. Depths are shown in mils (thousandths of
an inch).

9.4.2 Case study: Boiler tube corrosion thinning assessment

Applications involving the reduction-to-practice of pulsed thermography tech-
niques include an Electric Power Research Institute (EPRI) project to detect the ex-
tent of erosion/corrosion damage in power generation boiler tubes. The material in
this section is reprinted with permission from EPRI.
This application involved three tests on three prepared samples of representa-
tive boiler tube configurations conducted under laboratory conditions, followed by
an in-situ test on an actual section of boiler tubing to verify the technique. The
pulsed IR imaging equipment included a shrouded bank of xenon flash lamps with
104 Chapter 9

Figure 9.5 Examples of IRNDT images using thermal wave injection—see text for de-
scriptions (courtesy of Thermal Wave Imaging, Inc.).

Figure 9.6 Results of thermal image reconstruction on a graphite epoxy sample

(courtesy of Thermal Wave Imaging, Inc.).
Materials Testing 105

reflectors specially designed for enhanced flash uniformity, a CPU to synchronize

the data collection with the flash lamps, and a high-resolution IR camera.
The in-situ test was run on an external section of sidewall penthouse tubing, 20 ft.
wide ´ 15 ft. high, that had corrosion damage caused by a leaking roof. Ultrasonic
testing had indicated reduced wall thickness. The thermal image (Fig. 9.7) verified
the presence of all the thinning detected by ultrasound and also indicated the extent of
the thinning along the tubes. For comparison, Fig. 9.8 is a thermal image taken under
the same conditions of a section of new tubes not yet placed into service.

Figure 9.7 In-situ thermogram of a boiler tube section indicating areas of thinning
due to corrosion.

Figure 9.8 Thermogram of a new section of boiler tubing not yet put into service—no
thinning indicated.
106 Chapter 9

9.5 Infrastructure NDT

Active thermography has been applied successfully to the detection of voids and
other dangerous defects in large concrete structures such as runways, taxiways,
roads, bridges, and concrete roofs. In most of the documented work in this area, the
Sun serves as a source of uniform heat. After a day of the sun’s heating, large con-
crete expanses such as runways can be expected to be uniformly warm. Subsurface
voids and erosion in the concrete cause changes in thermal capacity and conductiv-
ity within the concrete, resulting in observable variations in surface temperature.
As in thermographic roof surveys, these anomalous indications may be mis-
leading and should be confirmed with a backup test discipline. Ground-penetrating
radar has been used successfully as a backup discipline to thermography in concrete
void detection. Examples of this multidisciplinary approach are provided in the pa-
per “Infrared remote sensing of hidden subsurface voids in large concrete struc-
tures,” G. J. Weil, Proc. SPIE 3436, Infrared Technology and Applications XXIV
(1998).
Chapter 10

Product and Process

Monitoring and Control

10.1 Evolution of Noncontact Process Control

The first rule of noncontact temperature measurement is that it is almost always a
surface measurement. The sensor is pointed at a spot on the surface of the product
and measures the IR radiation from this spot. The instantaneous size of the target
spot depends on the sensor’s collecting optics and the working distance to the tar-
get. The measurement is made in radiance and converted to an equivalent tempera-
ture value, if needed, by inserting a correction for the measured or estimated target
surface emissivity. Typically, the decision to control a process is not made until a
simple IR sensor is deployed and data are gathered over a period of operating time,
under a variety of expected operating conditions, and at different points in the pro-
cess. The condition (quality, consistency, etc.) of the product is correlated to the
temperature variations experienced at the various monitored locations. The point
(or points) in the process where temperature behavior is most closely related to
product condition is selected as the permanent monitoring/control site (or sites).
Variations in signal at this site are used to control the process. This can be done
manually, with an observer maintaining the temperature reading within allowable
limits by manually turning the process on and off, or by adjusting the process driv-
ing control (gas valve, heater current, speed adjustment, etc.). The trend, however,
is to close the loop by means of a computer/data processor for automatic control of
the process. The three control types described above—monitor, open-loop control,
and closed-loop control—are illustrated in Fig. 10.1.
The schematic of Fig. 10.2 illustrates a typical configuration for process control
using multiple sensors and multiple control outputs. Modern IR sensors are as ver-
satile electrically as conventional sensors; analog signals of current or voltage,
BCD digital signals, linear with radiance, or temperature are all available. The sen-
sor outputs are fed, along with other signals (pressure, humidity, moisture, flow
speed, etc.) into the universal data acquisition interface. From this point the appro-
priate control mode, be it proportional (P), proportional plus integral (PI), propor-
tional plus integral plus differential (PID), or any of a number of advanced control
options, is selected by the control system designer. Madding’s paper, referenced
above, provides an in-depth discussion of modern process control strategies.

107
108 Chapter 10

Figure 10.1 Three methods of accomplishing process control (revised and reprinted
from R. P. Madding, “Infrared sensors and process control,” Proc. SPIE 446, Thermo-
Sense VI, 1984, pp. 9–17).

Figure 10.2 Typical configuration for multisensor process control (courtesy of Raytek,
Inc., a Fluke company).
Product and Process Monitoring and Control 109

10.2 Full Image Process Monitoring

Infrared scanning and imaging systems can be used when measurement of one
point in the process, or even a number of points, is not considered adequate to char-
acterize the process for successful control. The most significant thing about this ap-
proach is that it is unique and unprecedented. Infrared point sensors are used, when
appropriate, in place of conventional temperature sensors, but IR scanners and
imagers are the only practical means to acquire a high-resolution thermal map of an
entire surface in real time (at or near TV rates). Furthermore, prior to the integration
of computers and image-processing software with thermal scanners, noncontact
full-surface thermal process control could not be considered.
When processes are in constant and uniform motion, an imaging system may
not be required to cover the full process image. To monitor and control processes in
motion, an IR line scanner can be used, scanning normal to the process flow, to gen-
erate a thermal strip map of the product as it passes the measurement site line (see
Fig. 2.18). If more than one measurement site line is required, additional line scan-
ners can be deployed. Alternately the line scanner can be set in motion to produce a
thermal map of a nonmoving process, as shown in Fig. 10.3.
In this case, a high-resolution scanner is used to monitor the electrolytic cells in
the tankhouse of a zinc refinery, where acres of acid-filled tanks contain pure metal
anode “starter” plates onto which the refined metal is deposited electrolytically
from unrefined cathodes in close proximity. When contact short circuits occur be-
tween electrode pairs in the tankhouse, metal production between the shorted pairs
is halted, excessive current flows, and power is wasted. An IR scanner, mounted in
a fiberglass environmental enclosure on the same overhead crane used to deposit
and remove electrodes from the acid bath, maps the process and pinpoints the
shorts, allowing service personnel to clear them with minimal exposure to toxic
acid fumes. The shorts appear as hot spots on the computer-monitored thermal map.

Figure 10.3 Electrolytic tankhouse scan where interelectrode shorts appear as hot
spots.
110 Chapter 10

They disappear after the shorts are cleared, and the process returns to normal. The
scanner communicates with the tankhouse host computer via a wireless photonics
link, providing statistical trending and a complete thermal history of the process.
This data can be used to determine total power consumption and energy efficiency.

10.3 Product Monitoring of Semiconductors

In the design, production, and quality control of semiconductor devices the thermal
budget is usually critical. Tiny electronic devices, a few microns across or smaller,
are mounted on (or integrated into) thin substrates. Operation generates heat, and
the management of this heat is essential to the efficiency and reliability of these de-
vices. The integration of high magnification IR optics and high-resolution FPA de-
tectors makes it possible to produce thermal images of these microscopic targets
during operation, with spatial resolution down to 2.5 µm, and to thereby monitor
performance and reliability.
Another consideration in thermal imaging of semiconductor devices is the
emissivity variation over the surface. Typically, these devices are constructed from
materials with widely ranging emissivity values, from near unity for ceramics and
oxides, to below 0.1 for gold and other unoxidized metals. As reviewed in Sec. 4.4.1,
measurement routines and diagnostic software have been incorporated into
high-resolution imagers to provide a spatial emissivity correction based on the ac-
tual measurement of the effective emissivity distribution of the target. By means of
a precision-controlled heated substage, the operator heats the unpowered device to
two known temperatures in sequence. At each temperature a radiance image is re-
corded. Using the known temperature and the known radiance for two temperatures
the emissivity matrix is computed, pixel-by-pixel, and stored. This matrix is subse-
quently used to correct the powered radiance image of that specific device and to
provide a “true temperature” thermogram. This is illustrated in Fig. 10.4.
The upper images are radiance thermograms of an unpowered sample device
(a) and the powered device (b). The emissivity matrix is at the lower left (c), and the
“true temperature” thermogram is at the lower right (d). The small hot areas at the
center of the temperature thermogram are not evident on the radiance images. The
spatial resolution of the images shown is about 25 µm.

10.4 Steel Wire Drawing Machine Monitoring

Heating occurs as steel wire is drawn through a hard die to reduce its diameter. This
frictional heating can be detrimental to wire quality if not controlled, as illustrated
in Fig. 10.5. The thermogram of the capstan on the left illustrates proper cooling
immediately after a reduction step. The thermogram of the capstan on the right il-
lustrates uneven cooling, which may lead to product degradation. Thermograms
such as these are routinely used in monitoring the wire drawing process in order to
adjust the process and optimize the quality of the final product.
Product and Process Monitoring and Control 111

Figure 10.4 Quadrant display of a device under test showing (a) unpowered radi-
ance, (b) powered radiance, (c) emissivity, and (d) “true temperature” (courtesy of
Quantum Focus Instruments, Inc.).

Figure 10.5 Wire drawing machine capstan thermograms showing (a) proper cool-
ing, and (b) improper cooling (courtesy of SI Termografia Infrarroja).
112 Chapter 10

10.5 Glass Products Monitoring (Spectral Considerations)

Monitoring glass products has proven to be a successful application of thermal im-
aging by exploiting the spectral characteristics of glass. Figure 10.6 shows the spec-
tral transmission characteristics of several thicknesses of glass lamp envelopes and
the operating spectral band of the camera used in the measurement (about 2–6 µm).
When a 2.35-µm band-pass filter is used, the envelope is virtually transparent and
the camera measures the filament temperatures (upper thermogram). When a
4.8-µm high-pass filter is used, the glass appears opaque and the camera measures
the glass surface temperature (lower thermogram).

10.6 Full Image Process Control

Whether a line scanner or an imager is used as the basic sensor, full image process
control can be defined as using an IR thermal image as a model against which to
compare, and thereby control, part or all of the thermal surface characteristic of a
product or process. The control method is similar to that used in point-sensing ap-
plications, although far broader in scope. The scanner or imager is first used to char-
acterize the thermal map of the product under ideal conditions. This is called the
criterion image—what the ideal thermal distribution would be if the process re-
sulted in perfectly acceptable products as designed. The digital value of each pixel
of the criterion image is stored.
Critical areas on the map such as welds and corners are examined, and allow-
able tolerances are applied based on product experience—that is, the allowable
variation is determined by its resultant effect on the end product quality. During the
actual process, the thermal map, or any critical portion of the map, is constantly
compared to the stored criterion image model by means of image subtraction and/or
statistical analysis techniques. (Image subtraction techniques are used when tem-
perature drift and registration between the criterion image and the test image can be
controlled. Statistical analysis techniques are used when they cannot.) The differ-
ences produced by this comparison are used to adjust or correct the settings of the
process mechanisms that govern the heat applied, or to alarm and automatically re-
set the process.
The most practical way to develop a criterion image is to make on-site mea-
surements. This entails continuous recording of thermal maps of the process over a
period of time during which acceptable product is being manufactured, and com-
puter-averaging these maps. If the process is not yet in operation, or if the existing
process does not produce acceptable products, a computer-generated design-based
criterion image is used.
The next step is to determine a tolerance matrix. This is the maximum global or
local deviation from the criterion image that will still result in acceptable product.
This step requires expert inputs from the process engineer, who has the most inti-
mate knowledge of the process, and knows which site points are most thermally
critical to product quality. Since the tolerance matrix exists only in software, it is
Product and Process Monitoring and Control 113

Figure 10.6 Using the same imager with different filters to measure temperatures of
the filaments (top thermogram) and the glass envelope (bottom thermogram)
(courtesy of FLIR Systems, Inc.).
114 Chapter 10

not prohibitive to start with a very narrow tolerance band and to widen the band as
practical considerations warrant.
Next is the implementation of controls. The number of control elements de-
ployed usually governs the tightness with which control of the thermal map can be
accomplished—but also, to a great extent, the cost of the control system. Here also,
on-line IR monitoring of an existing process can help determine what additional con-
trol elements are necessary to bring the product within acceptability limits.
The next step, and a most significant one, is the development and implementa-
tion of the algorithm that characterizes the effect of each of the control elements on
the overall thermal map of the process. While this algorithm can be calculated theo-
retically, it is more practically accomplished through statistical analysis of actual
on-site experimental measurements.

10.7 Closing the Loop—Examples

Finally, the control routine is written, using display screen graphics and a keyboard,
and the loop is closed. A simple example of such a routine is illustrated in Fig. 10.7. In

Figure 10.7 Thermal image process control using a line scanner and set points (cour-
tesy of FLIR Systems, Inc.).
Product and Process Monitoring and Control 115

this simulated example, an IR line scanner is aimed at a critical site line in a sheet pro-
cess, scanning normal to the process flow. The upper display is the criterion image, in
this case a single line scan defining the ideal shape of the thermal distribution across
the process. This shape is managed by six set-point relays, three high and three low,
that control heaters located upstream in the process from the site line. Values for the
high set points (above the scan line) and low set points (below the scan line) are en-
tered into the keyboard. The control system then works to maintain the shape of the
thermal profile always in the safe (black) region. The lower display shows the result-
ing distribution of this profile with time, always within the preset acceptable limits.
Another practical example is related to the non-uniform heating of plastic
blanks moving through an oven prior to being molded. The aim here was a uniform
surface temperature of 300°F. The configuration of the oven, however, resulted in a
basic heat pattern non-uniformity which, combined with ambient temperature vari-
ations from site to site and blank indexing variations, typically produced a thermal
map similar to the 3D strip map presentation shown in Fig. 10.8(a). The net result
was an unacceptably high rejection rate for the finished parts.

Figure 10.8 Full image process control using a line scanner and multiple zones:
(a) before implementation of full image process control; (b) after implementation of
full image process control (courtesy of FLIR Systems, Inc.).
116 Chapter 10

To implement full image process control, an IR line scanner is placed at the

oven exit, scanning across each blank as it leaves the oven. The forward movement
of the part, combined with the fast response of the line scanner, provides the full
thermal map to the computer. A full statistical control chart is software-generated,
based on mean temperature and standard deviation over the entire surface. The
oven heater is zoned and the computer interfaced to a relay control board with one
relay managing a set-point controller for each zone. The statistics for each control
zone are calculated based on the corresponding section on the part, and a
closed-loop statistical process control algorithm is implemented. The result is seen
on the 3D strip map presentation shown in Fig. 10.8(b). The color hues indicate
temperatures in accordance with the scale at the left. The control level temperature
is about 300°F.
Chapter 11

Night Vision, Security,

and Surveillance

11.1 Introduction
The earliest development of thermal IR imaging systems was based on military re-
quirements for night vision capability. The first night vision devices were of the
“star scope” variety, based on radiance amplification or “image intensification” of
available light. Early military star scopes used NIR illuminators that could be de-
tected by enemy sensors, and so offered limited military advantage. These were
eventually replaced by “undetectable” passive image intensifiers based on high
sensitivity GaAs photocathodes. The first truly passive thermal night vision devices
operated in the IR and were based on the detection of thermal radiation from the tar-
get surface. For more than half a century, from the introduction of the first thermal
IR devices through the current development of uncooled IR FPAs, the military has
continued to be a driving force in this evolution. In the aftermath of the 9/11 attack
in the U.S. and the worldwide SARS outbreak in 2002–2003, increased awareness
of the need for homeland security has placed a strong emphasis on wider deploy-
ment of IR instrumentation for surveillance and threat detection.
Unlike the needs of most industrial applications, thermal imagers for night vi-
sion, security, and surveillance applications require little or no temperature mea-
surement capability. The key requirement here is to present an image of the target
with the best possible spatial and thermal resolution, at the greatest possible dis-
tance from the target, under the worst conditions of obscuration and absorption in
the intervening atmospheric path, and without the possibility of detection by enemy
sensors.
Since instruments used for these applications usually need to detect and iden-
tify tactical targets through atmosphere in the dark and in bad weather, they gener-
ally operate in the 8–12 µm spectral window where the atmosphere has very little
absorption. Exceptions to this are IR seeking and homing sensors that are sensitive
to specific target emission signatures, such as rocket engine plumes. These instru-
ments usually operate somewhere in the 3–5 µm region.
During the Gulf War in the early 1990s, U.S. citizens were made aware of some
of the weapon enhancement capabilities of IR imaging through the news media,
and the entertainment media continues to illustrate (and sometimes exaggerate)

117
118 Chapter 11

current surveillance capabilities. The purpose of this brief chapter is to provide an

overview and some illustrations of both military and nonmilitary applications.

11.2 Comparing Thermal Imagers with Image Intensifiers

An image intensifier is a device with an electronic tube equipped with a light-sensi-
tive electron emitter at one end and a phosphor screen at the other. This device is
used in astronomy and in military and nonmilitary surveillance systems to provide
night vision. An image intensifier amplifies available visible and NIR (0.3–0.9 µm)
light reflected off the target surface and therefore cannot operate in total darkness.
An IR thermal imager is a device that senses self-emitted IR radiation, propor-
tional to temperature, from the surface of a target and converts it to an image, where
the brightness (or color hue) is proportional to the intensity of energy emitted from
the surface. The presence or absence of visible light has little or no effect on a ther-
mal imager. It is used in both military and nonmilitary applications.

11.3 Homeland Security and other Nonmilitary Applications

Specific nonmilitary areas of applications include the following:

· Aerial-, ground-, and sea-based search and rescue

· Firefighting
· Space and airborne reconnaissance
· Police surveillance, crime detection, and security
· Driver’s aid night vision

11.3.1 Aerial-, ground-, and sea-based search and rescue

Thermal imagers, both hand-held and gimbal-mounted, are used extensively for
search and rescue operations. High resolution thermal imagers allow search and
rescue personnel to locate and identify wreckage and personnel in the sea by ther-
mal signature, even at great distances and under adverse weather conditions. The
8–12 µm atmospheric window in which they operate provides optimum night and
day detection through fog and mist. Figure 11.1 is a thermogram of a vessel at sea in
night fog.

11.3.2 Firefighting and first response

The same qualitative thermal-imaging instruments have been adapted to fire detec-
tion applications. From the ground or the air, these instruments detect incipient fires
and unextinguished portions of forest fires. Firefighters report that at most struc-
tural fires they don’t see flames, just dense smoke. The 8–12 µm spectral band in
which the instruments operate also provides improved visibility (less absorption
Night Vision, Security, and Surveillance 119

Figure 11.1 Thermogram of a vessel at sea at night in fog (8–12 µm) (courtesy of FLIR
Systems, Inc.).

loss) through smoke. This allows the quick location of victims in smoke-filled
structures; also, the source of the fire can be located rapidly to help save even more
lives as well as the structure. For other first responders, thermal imagers can pro-
vide rapid location of intruders and danger points and help in the location of living
victims. Adaptations of military helmet-mounted thermal imaging displays are be-
coming standard equipment for firefighters and other first-response teams.

11.3.3 Space and airborne reconnaissance

Although most reconnaissance applications are related to military applications,
thermal imagers continue to find uses in weather reconnaissance, location and mon-
itoring of volcanic activity, location and tracking of natural thermal currents (the
Gulf Stream) as well as man-made thermal effluents from power generation facili-
ties, and even the location and tracking of schools of fish by the associated sea sur-
face thermal activity.

11.3.4 Police surveillance and crime detection and security

Since 1995, selected police cruisers have been outfitted with portable, low-cost
night vision imaging systems that have been effective in crime interdiction. Built
around uncooled IRFPA detectors, these systems allow police to approach sus-
pected crime areas in total darkness. Combined with helicopter-mounted systems,
these systems have also allowed the pursuit and apprehension of suspected offend-
ers in darkness with reduced risk to law enforcement personnel. The same technol-
ogy has been applied to perimeter and zone protection thermal imaging devices to
warn of intruders in critical areas such as nuclear facilities. Figure 11.2 is a
thermogram of an intruder at night taken at a distance of greater than 100 yards.
120 Chapter 11

Figure 11.2 Thermogram of an intruder at night (8–12 µm) (courtesy of FLIR Systems,
Inc.).

Cool area
reveals hidden
compartment

Figure 11.3 Hidden compartment in a vehicle (courtesy of BAE Systems).

Thermal imaging has been used at border crossings to detect hidden compartments
in vehicles, as illustrated in Fig. 11.3. The space inside the compartment forms a
thermal barrier between the engine and the surface, causing the surface temperature
to be cooler.

11.3.5 Driver’s aid night vision

Since 1998, when Cadillac first offered driver’s aid night vision packages, drivers
of both passenger vehicles and trucks have benefited from the advantages of these
devices. Based on uncooled IRFPA technology, these devices operate in the
8–12 µm spectral region. They provide drivers with enhanced vision through
smoke, fog, and drizzle, and extend their ability to see humans, animals, and other
Night Vision, Security, and Surveillance 121

Figure 11.4 Driver’s thermal image (top) compared to visible image (bottom) (cour-
tesy of FLIR Systems, Inc.).

warm objects well beyond normal headlight range. Figure 11.4 is a comparison of
the driver’s thermal view (top) with a visible image of the same scene (bottom).
Figure 11.5 is a high-resolution thermogram taken of freeway traffic at night.

11.3.6 New thermal image fusion applications

Figure 11.6 illustrates the fusion of a thermal and a visible image from a smoke trial
to simulate battlefield conditions. The scene in the visible image (a) is obscured by
the smoke. The thermal image (b) shows thermal events clearly but hides some of
the visible details. The fused image (c) reveals both visible and thermal details with
true registration. The fusion algorithm is proprietary to Waterfall Solutions.

11.3.7 New military applications

Military applications of thermal imaging technologies include search and rescue, tar-
get surveillance, threat detection and assessment, weapons and mines detection, and
weapons and missile guidance. Figure 11.7 shows a military helicopter in flight and
illustrates the resolution capabilities of modern night vision surveillance systems.
122 Chapter 11

Figure 11.5 Thermogram of freeway traffic at night (8–12 µm) (courtesy of FLIR Sys-
tems, Inc.).

Figure 11.6 (a) Visible, (b) thermal, and (c) fused images with smoke (courtesy of
Waterfall Solutions, UK).

Figure 11.7 View of a military helicopter from the ground (courtesy of SI Termografia
Infrarroja).
Chapter 12

Life Sciences Thermography

12.1 Introduction
Perhaps the earliest nonmilitary application of thermal IR imaging was in the field
of health care diagnostics. As early as the late 1950s, a slow-scan thermal imager
(six minutes per scan) was applied to the early detection of breast cancer and incipi-
ent stroke. This approach was based on the reasoning that in any warm-blooded
creature, a disruption of normal function would produce a temperature change,
most often resulting in a skin temperature deviation. It was further reasoned that
since one side of the human body is for the most part a mirror image of the other,
temperature variations between the left and right sides would very often indicate
abnormalities. This reasoning proved correct, and although hampered by early op-
position from many in the medical profession, IR thermal sensing and imaging
(also known in the medical field as thermology) continues to be applied to human
and veterinary medicine, biological studies, and other areas of life sciences diag-
nostics and research. This chapter illustrates some examples.

12.2 Thermography as a Diagnostic Aid in the Early Detection

of Breast Cancer
Breast cancer screening is based on the principle that chemical and blood vessel ac-
tivity in both precancerous tissue and the area surrounding a developing breast cancer
site is almost always higher than in the normal breast. Since precancerous and cancer-
ous masses are highly metabolic tissues, they need an abundant supply of nutrients to
maintain their growth. In order to grow, a cancerous mass increases blood circulation
to its cells by producing chemicals that keep existing blood vessels open, recruit dor-
mant vessels, and create new ones. This process (neoangiogenesis) increases regional
surface temperatures of the breast. Figure 12.1 compares thermograms of three pa-
tients showing a normal thermogram (a), fibrosystic changes (b), and an early stage
malignant tumor (c).
According to a 1997 report by the American Society of Clinical Oncology,
thermal changes in breast tissues have been demonstrated to show up well in ad-
vance of masses that appear in mammograms.*

*
“Infrared imaging as a useful adjunct to mammography,” Oncology/Oncology News International
6(9), September 1997.

123
124 Chapter 12

Figure 12.1 Sample breast thermograms of three patients: (a) normal, (b) fibrosystic
changes, and (c) early stage malignant tumor (courtesy of Meditherm).

Both lateral
views were
normal
Primary or
Secondary
Lesion

Centerline of the
Dog’s Back

Figure 12.2 Confirmed inflammations at two different locations on a dog’s back (cour-
tesy of FLIR Systems, Inc., the InfraMation 2000 conference, and Donna L. Harper, DVM).

Thermography is also used in sports medicine, chiropractic, and other disciplines

where stress and pain produce elevated local skin temperatures.

12.3 Veterinary Medicine

Figure 12.2 illustrates thermographic confirmation of intervertebral disk disease
(IVD) in a five-year-old springer spaniel. This dog had painful symptoms that indi-
cated IVD for six months, but all the x rays taken during this time showed normal
skeletal structure without degenerative changes. The thermogram revealed inflam-
mation at two different locations on the dog’s back to allow a definitive diagnosis of
early IVD and avoid additional diagnostic efforts.

12.4 Biological and Threat Assessment Applications

Biological applications of IR thermography range from crop disease surveys to
wild animal herd population assessments and fish migration patterns.
Life Sciences Thermography 125

Figure 12.3 Thermographic results of SARS screening: (a) normal subject, and (b) fe-
brile subject (courtesy of Meditherm).

The importance of threat assessment screening was illustrated by the

2002–2003 SARS epidemic and the more recent threat of avian flu. Typical airport
screening results are illustrated in Fig. 12.3. Image (a) shows a normal subject with
a maximum skin temperature of 37.53°C, and image (b) shows a febrile subject
with a maximum skin temperature of 38.67°C who then becomes a candidate for
further testing. The temperature scale is shown below the images.
Appendix A

Commercial Instrument
Performance Characteristics

Manufacturer Models Characteristics

A. Point Sensing
1. Probes and IR thermocouples
Everest 3800 series Thumb-size sensor with remote ana-
log output, 8–14 µm, ranges from 40
to +1100°C.
Exergen SmartIRt/c, powered Wide range of IR thermocouples with
ITt/c series, and standard and custom configurations.
SnakeEye series
Horiba IT550 32–572°F, 0–300°C, LCD display,
e set, hold button.
Linear quickTEMP, C500, –18 to +315°C, quickTEMP has LCD
C1600, and C1700 display and optional laser pointer. C500
series connects to a multimeter, C1600 has
multiple models with various ranges,
some models have e set. C1700 reads
heat flow in BTU/sq.ft./hr
Mikron M50, M500 IR Various temperature ranges from
thermocouples, 0–500°C.
MI-TS300, and
MTD100 heat
switches
Omega OS36, OS37, Modular and hand-held IR thermo-
and OS38 series IR couples, various ranges.
thermocouples
OS200, 500, 600, Close focus probes with LCD read-
88000, and OS20 outs.
series

127
128 Appendix A

Manufacturer Models Characteristics

1. Probes and IR thermocouples (continued)
Dickson D166 and 180 Various models –40 to +950°F, –45 to
series +538°C, hold button, LCD display, la-
ser pointer, emissivity control (e set).
Everest 100.3ZL and ZH, Several models from –30 to +1100°C,
6110.4ZL, LCD display, analog output, Vario-
6130.4ZH, 6000.1 Zooom™ aiming light, peak sampler,
Vario-Zooom™ differential available, rechargeable
battery.
Exergen Medical and veteri- Contacting IR temperature sensors for
nary temperature temporal artery, ear, and skin mea-
sensors surements, many models.
DX series Close-up sensor with reflective cone
for target emissivity correction; ran-
ges from –4.5 to +871°C, digital
readout.
MicroScanner E Series of devices that measure temper-
and Super E ature differentials by scanning the col-
lecting beam rapidly, several models.
Fluke Raynger Various models from –30–900°C,
MiniTemp, MX, 3I, dual LCD display, hi-lo alarms,
ST series RS232/analog output, datalogger;
max, min, mean, and differential; la-
ser aiming available.
Ircon ULTIMAX and Various models from –30 to
Ultimax Junior +3000°C, thru-the-lens sighting,
series spectral ranges 0.65, 0.96–1.06 and
8–13 µm (some models are
ratiopyrometers), LCD display, ana-
log and RS-232 outputs, replaceable
batteries.
Irtronics Sniper series Laser or visual sights, 8 wavelengths,
0–3000°F/C.
Land Cyclops series High- and low-temperature
(Minolta), (to 5500°C), small targets, variable
PockeTherm 30, focus, reticle display. Compac 3 is
30A, 31, 32C, low-temperature, fixed focus,
Compac 3 thru-lens sight.
Commercial Instrument Performance Characteristics 129

Manufacturer Models Characteristics

1. Probes and IR thermocouples (continued)
Linear LT, LTL, and LTS –29°–1093°C, 30:1 or 60:1 optics, la-
series ser pointer or nonparallax sight avail-
able, 1% accuracy, F-C switch, LCD
display.
Mikron M90, MIS, GA8, Various models, including ratio py-
M120, M125, and rometers, from –40 to +3000°C, LCD
Quantum 1 displays. Options: laser aiming light,
telescope, e set, various FOVs. Quan-
tum 1 has laser reflection emissivity
calculation and correction feature for
high-speed targets.
Omega HHM, OS520, Wide range of models with tempera-
OS631, OS900 ture ranges from –18–2482°C. Options
series, others include laser aiming, through-the-lens
viewing, BTU readout.
Palmer Wahl Heat Spy DHS-20 Various models from –40 to
series, DHS 30 +1760°C, analog, LCD and LED dis-
series, DHS 85 series, plays. Series DHS has e set,
DHS 520 series, peak-hold, and various FOVs includ-
DHS 100 series, ing telescopic. Through- the-lens
DHS-200 series, sighting and laser aiming features are
DHS-34 series, available.
DHS-53 series,
HAS-201 series
Pyrometer Pyrolaser laser Ranges from 600–3000°C, uses laser
pyrometer to measure reflectance and correct for
emissivity, thru-lens sights, recharge-
able battery.
Pyrofiber series Fiber optic coupled, ranges from
600–3000°C, uses laser to measure
reflectance and correct for emissivity,
thru-lens sights, rechargeable battery.
Quantum Logic QL1300 Laser/microcomputer pyrometer; ran-
ges from 350–3000°C; uses laser to
measure reflectance and correct for
emissivity; uses narrow-band inter-
changeable filters from 0.9–3.9 µm;
on-line models available.
130 Appendix A

Manufacturer Models Characteristics

1. Probes and IR thermocouples (continued)
Teletemp INFRAPRO 3 Various models from –32–+760 °C, re-
and 4, High Value, chargeable battery, e set, LED display.
and DT1100 Laser aiming and scope available.
Williamson 600, Viewtemp, Viewtemp is 25–1650°C, LED inside
Truetemp reticle, e set, rechargeable battery.
Truetemp is 2–color, 550–2200°C.
Model 600 has analog display, vari-
ous ranges from 75–3000°F.
3. Point sensing on-line
E2 Technology Heat switch (Solar Various heat pulse switches and
(now part of TD100 and Meteor ruggedized models from 260–1650°C,
Mikron) 300), Pulsar, and including ratio pyrometers.
Quasar series
Everest 3000 and 4000 Ranges from –40 to +1100° C, spot size
series available down to 0.01 in. Multiplexes
up to 8 heads through electronics.
Horiba IT-230 0–300°C, multiple ranges, digital out-
put with e-set, multiple control fea-
tures.
Ircon Modline 3 and 4 Various models and accessories, –18
series; SA, SR, and to +1375°C, integrated, fixed focus,
1100 series; Jave- 2-wire transmitters, spectral selection.
lin, Mirage, and Various models of 2-piece, –18 to
MiniIRT series; +3600°C with thru-lens sights, LCD
others display, spectral selection (including
ratio pyrometers), and control and
output options. IR pulse switches and
fiber optic coupled heads.
Irtronics Argosy, others Various ranges from 30–3000°C,
spectral selection, telephoto,
multizones, fiber optic coupled heads
available.
Land System 4, SOLO, Wide selection of instruments,
UNO, CF series 120–2600°C, 2-color, spectral selec-
tion, fiber optic, telephoto lens option,
modular, many accessories. SOLO is a
line of 2-wire thermometers.
Commercial Instrument Performance Characteristics 131

Manufacturer Models Characteristics

3. Point sensing on-line (continued)
Linear TM1000 series, TM1000 series are modular sensors,
M series, ranges from 0–2000°C, spectral se-
MX series lection, thru-lens sights, linearized
outputs, many control options. M se-
ries is lower cost but has fewer op-
tions. MX series consists of
customized units with
high-temperature and high-resolution
options.
Mikron M67 series Modular, ranges from 0–1650°C, spec-
tral selection, fixed and variable focus,
thru-lens sights, many accessories.
M68, M668, M600, Fiber optic, one color and ratio py-
M680 M770, rometers, ranges from 250–3500°C.
M780, MI series
M190 series 2-piece, 0–3000°C, spectral selection,
fixed and variable focus, thru-lens
sights, many accessories.
M77/78, others M77 is 2-color. M78 is 2-color, fiber
optic coupled.
Omega OS36, 39, 42, 65, Wide range of sensors including fi-
101, 1592 series, ber-optic coupled, ranges from –45 to
many others +3700°C.
Raytek (Fluke) Thermalert TX Various models, –18 to +2000°C, set
series points, e set, processing options,
spectral selections.
Compact series Intended for low-cost, multi-
ple-sensor applications.
Marathon series For high-temperature applications, up
to 3000°C, 1 µm spectral region, in-
clude ratio pyrometer and fiber optic
coupled models.
Williamson PRO-4-, PRO-50, Various models including 2-color, fi-
PRO 80, PRO 90, ber optic coupled, 30–2500°C, spec-
PRO 100, tral selections, many accessories.
PRO 200
132 Appendix A

Manufacturer Models Characteristics

3. Point sensing on-line (continued)
Williamson TempMatic 4000, Various models; ranges from
(continued) FiberView 5000, 30–2500°C; 2-wire, fixed focus trans-
500, 700, and 1000 mitters; 2-wire, fixed focus, sin-
series, TransTemp gle-wavelength and ratio pyrometers;
series some fiber optic coupled models.
B. Line Scanners
AIM LINAR, TMS35 Modular, Stirling-cycle-cooled HgCdTe,
288 ´ 4 array available in 2 wave-
lengths: 3–5 µm and 8–10 µm. TMS35
has temperature measuring capabili-
ties.
HGH (France) TERMASCAN Modular optomechanically scanned,
thermoelectrically cooled, PbSe or
HgCdTe detectors, 3–5 µm, high- res-
olution analog and digital outputs;
operates with control system host
computer.
Ircon ScanIR II series Modular, optomechanically scanned,
thermoelectrically cooled and un-
cooled detectors for various spectral
bands from 1–5.1 µm; high-resolution
analog and digital outputs; visible la-
ser alignment feature; operates with
host computer.
Land Landscan LS series Modular, optomechanically scanned,
adjustable scan rate; 6 models with
wavelengths from 1–5 µm, tempera-
ture ranges from 70–1400°C,
high-resolution analog and digital
outputs; operates with control system
host computer.
Mikron MikroLine series, 128, 160, or 256-element arrays of
2250, 2128, 2256 PbSe, pyroelectric, or GaAs and other
detectors; temperature ranges of
0–1300°C; spectral ranges of
1.4–1.8 µm, 3–5 µm, 4.8–5.2 µm and
8–14 µm; frame rates up to 18 kHz;
full process analysis software.
Commercial Instrument Performance Characteristics 133

Manufacturer Models Characteristics

B. Line Scanners (continued)
Raytek (Fluke) CS-100, GS-100, Optomechanically scanned; each sys-
TF-100, TIP-450 tem for a different process application,
(all using the modular thermoelectrically cooled, high-
MP-50 Thermalert resolution analog and digital outputs;
line scanner) various wavelengths; operate with inte-
gral control system or host computer.
Thermoteknix Centurion and Optomechanically scanned; using
WinCem thermoelectrically cooled, HgCdTe
detector, 3.5–4.2 µm, high-resolution;
temperature range 100–700°C, exten-
sive diagnostic and visualization soft-
ware.
C. Thermographic
1. Optomechanically scanned cameras
Jenoptik Varioscan series Stirling-cycle-cooled, liquid nitro-
gen-cooled, and TE-cooled HgCdTe
detector models for 8–12 and 3–5 µm
performance; 30-deg ´ 20-deg FOV
slow scan, high sensitivity, extensive
diagnostic software.
2. Cameras, FPA, nonmeasuring
AIM µCam, FS, HuntIR, Modular, building block cameras us-
and FL FLIR Fam- ing cooled HgCdTe, GaAs QWIP and
ilies PtSi FPAs from 128 ´ 128 element to
640 ´ 486 element.
AXSYS Cadet 75 Thermal imager for security and sur-
veillance; lightweight (3.5 lbs), features
uncooled 320 ´ 240 element microbo-
lometric FPA detector for 8–14 µm op-
eration, battery powered, monochrome
display, optional visible channel.
Viper XP Thermal imager for firefighting appli-
cations, special wide-field (75 deg)
viewing with rotating display, features
uncooled 320 ´ 240 element micro-
bolometric FPA detector for 8–14 µm
operation, battery powered, mono-
chrome display, with color isotherms.
134 Appendix A

Manufacturer Models Characteristics

2. Cameras, FPA, nonmeasuring (continued)
BAE MicroIR Uncooled 320 ´ 240 element micro-
bolometric FPA imager module in a
weatherproof, ruggedized housing.
Electrophysics PV-320A, 320M Uncooled barium-strontium-titanate
(BST) IRFPA imager, 2–14 µm or
0.6–20 µm 320 ´ 240 element array,
60-Hz frame rate, quantifiable option.
(PV320T has temperature measure-
ment capability).
PV320T Has temperature measurement capa-
bility added.
FLIR ThermaCAM E Uncooled miniaturized (less than 1.5
series lbs) 160(H) ´ 120(V) element micro-
bolometer FPA, portable, battery
powered, 7.5–13 µm, laser aimer,
nonmeasuring version.
SCOUT series Hand-held night vision imagers us-
ing uncooled microbolometer FPA
detectors, for security and surveil-
lance.
Sapphire, Ultra, Multipayload packaged systems for
and Star series commercial and military applications
featuring high resolution Stirling-
cycle-cooled InSb FPA (3–5 µm) and
QWIP FPA (8–9 µm) detectors.
(FLIR offers many other security and
surveillance-related products de-
scribed on its website).
Guangzhou SAT GF3000A Thermal imager for firefighting appli-
cations, features uncooled 160 ´ 120
element microbolometric FPA detec-
tor for 8–14 µm operation, battery
powered, monochrome display.
HGH VIGISCAN 11 High resolution 360 deg panoramic
scanner, cooled HgCdTe 288 ´ 4
array for perimeter security.
Commercial Instrument Performance Characteristics 135

Manufacturer Models Characteristics

2. Cameras, FPA, nonmeasuring (continued)
Horiba I21064A Uses 8 ´ 8 element thermopile array
to superimpose a colorized tempera-
ture grid over a visible image. Intro-
duced for SARS detection, 8–14 µm.
L3-Cincinnati Nightmaster, Night Many models of Stirling-cycle-cooled
Electronics Conqueror, others 160 ´ 120, 256 ´ 256 and 640 ´ 512
element InSb FPA imagers (3–5 µm)
for a wide variety of military, search,
and surveillance applications.
Marconi Argus series Firefighter thermal imagers.
Mikron MikroScan 7302, NIR cameras for ambient to 100°C
7402 for intrusion detection and seeing
through flames.
Mine Safety VideoTherm 2000 Uncooled 320 ´ 240 element
Appliance Corp. pyroelectric FPA hand-held viewer
with added measurement capability
by means of boresighted radiation
thermometer, monochrome or color
display (8–14 µm).
RedShift 160 Thermal Modular engine based on new
Camera RedShift patented thermal light valve
(TLV) technology; enables CMOS ar-
rays to convert thermal energy to visi-
ble images; uses 160 ´ 120 element
CMOS array.
Santa Barbara Various models High-resolution front end detector
Focal Plane and optics for integration into user’s
system, based on liquid nitro-
gen-cooled, 128 ´ 128 element
256 ´ 256, 320 ´ 240, 320 ´ 256,
640 ´ 480, and 512 ´ 512 element
InSb FPA detectors, 1–5 µm.
Thermoteknix MIRIC and Miniaturized uncooled modules us-
MIRICL ing microbolometric 164(H) ´
128(V), 384(H) ´ 288(V) and
640(H) ´ 480(V) element FPA
detectors, 7–14 µm.
136 Appendix A

Manufacturer Models Characteristics

2. Cameras, FPA, nonmeasuring (continued)
US Infrared THERMOviewer Portable, battery-powered, uncooled
BST 320 ´ 240 element IRFPA
imager, 2–14 µm spectral range,
60-Hz frame rate. Boresighted IR
thermometer provides spot measure-
ment reference; color display, aimed
at low-cost PdM applications.
Wuhan IR920, 922, and Uncooled microbolometer 320(H) ´
923 240(V) element FPA, 920 has image
radio transmitter and receiver. 922 is
helmet mount, 923 is long-range
monitoring/surveillance camera.
3. Cameras, FPA, radiometric (measuring)
AVIO (see TVS-200, 500, 700 Lightweight (3.5 lbs) unit featuring
Electrophysics uncooled 320 ´ 240 element micro-
for U.S. sales) bolometric FPA detector (8–14 µm),
temperature range –20 to +300°C, ex-
tendable to –40–2000°C, many diag-
nostic features, interchangeable lenses.
TVS-8500 Lightweight (3.5 lbs) unit featuring
Stirling-cycle-cooled 256 ´ 256 ele-
ment InSb FPA detector (3.5–4.1 and
4.5–5.1 µm), temperature range –40 to
+900°C, frame rate 120 Hz, many diag-
nostic features, interchangeable lenses.
Cedip (see
Electrophysics
for U.S. sales)
Electrophysic Jade MW Stirling-cycle-cooled 320 ´ 256 ele-
ment FPA MCT or InSb, 3–5 µm, ex-
tensive diagnostic software.
Jade LW Stirling- cycle-cooled 320 ´ 256 ele-
ment FPA MCT, 7.5–9.6 µm, exten-
sive diagnostic software.
Jade UC Uncooled 320 ´ 240 microbolometer
FPA, 8–14 µm, extensive diagnostic
software.
Commercial Instrument Performance Characteristics 137

Manufacturer Models Characteristics

3. Cameras, FPA, radiometric (measuring) (continued)
Electrophysics EZTherm series Lightweight (4.3 lbs) unit featuring
(continued) uncooled 320 ´ 240 BST FPA detec-
tor (7.5–14 µm), integrated flash
camera, temperature range –20 to
+250°C, stores more than 500 im-
ages, articulated sensing head, inter-
changeable lenses available.
HotShot series, LT, Lightweight (1.9 lbs) unit featuring
PRO, and XL uncooled 160 ´ 120 element microbo-
lometer FPA detector (7.5–14 µm),
integrated flash camera, temperature
range up to 500°C.
Silver 420M and High performance modular unit fea-
450M turing Stirling-cycle-cooled 320 ´
240 element InSb FPA (3.7–5.1 µm),
frame rates up to 1000 Hz, sensitivity
of < 20mK.
PV-320T Uncooled BST IRFPA imager, 2–
14 µm or 0.6–20 µm 320 ´ 240 ele-
ment array, 60-Hz frame rate, quanti-
fiable option included.
FLIR InfraCAM Low cost, lightweight (1.25 lbs) fea-
turing uncooled 120 ´ 120 element
microbolometer FPA, measurement
capability through post-processing.
ThermaCAM For building diagnostics, portable
B series (starting at 1.5 lbs), featuring
uncooled microbolometric FPA detec-
tors from 120 ´ 120 to 320 ´ 240 ele-
ments, 7.5–13 µm, extensive
diagnostic software.
ThermaCAM For various diagnostic applications,
E series portable (less than 1.5 lbs) featuring
uncooled microbolometric FPA detec-
tors from 160(H) ´ 120(V) to
320(H) ´ 240 (V) elements, 7.5–
13 µm, LCD display, laser aimer,
extensive diagnostic software.
138 Appendix A

Manufacturer Models Characteristics

3. Cameras, FPA, radiometric (measuring) (continued)
FLIR ThermaCAM P45 Uncooled high sensitivity micro-
(continued) ThermaCAM P65 bolometer 320(H) ´ 240(V) element
ThermaCAM FPA, portable, battery powered,
S65HSV 7.5–13 µm LCD display, extensive
diagnostic software. P65 has im-
proved sensitivity, laser aimer, added
LCD color display. S65HSV has laser
locater and visible camera.
ThermaCAM P640 High-performance unit featuring
uncooled 6420(H) ´ 480(V) element
high-sensitivity microbolometer FPA,
7.5–13 µm, portable, lightweight (2.6
lbs), integral, extensive diagnostic soft-
ware, laser aimer, LCD color display.
ThermoVision For automation applications, minia-
A series ture modules (starting at 0.26 lbs)
featuring uncooled microbolometric
FPA detectors from 160(H) ´ 120(V)
to 320(H) ´ 240 (V) elements,
7.5–13 µm, interchangeable optics.
ThermoVision HS High-resolution, high-speed models
and Researcher using 320 ´ 256 element FPAs, selection
series SC4000 and of detectors; InGaAs (0.9–1.7 µm) InSb
SC6000 (3–5 µm) or GaAs QWIP (8–9.2 µm),
programmable frame rate from 1–420 Hz.
ThermoVision Modular, compact units featuring
A20 series 160(H) ´ 120(V) element uncooled
microbolometer FPA detector,
7.5–13 µm, extensive diagnostic soft-
ware, many lenses available, includ-
ing microscope, low-cost industrial
automation camera.
ThermoVision Modular, compact units featuring
A40 series 320(H) ´ 240(V) element uncooled mi-
crobolometer FPA detector, 7.5–13 µm,
extensive diagnostic software, many
lenses available, including microscope,
low-cost industrial automation cameras.
Commercial Instrument Performance Characteristics 139

Manufacturer Models Characteristics

3. Cameras, FPA, radiometric (measuring) (continued)
FLIR Alpha Miniaturized, 160 ´ 128 element
(continued) microbolometer FPA, 7.7–13.5 µm.
Measuring capability by means of
added diagnostic software.
GasFindIR Special purpose instrument for locat-
ing and imaging gas leaks; features
Stirling-cycle-cooled 320 ´ 240 ele-
ment InSb FPA detector, 3–5 µm, and
a selection of interference filters for
the detection of various gases.
Merlin Family of imagers offering 320 ´ 256
element FPAs in four spectral bands:
InGaAs (0.9–1.68 µm, uncooled), InSb
(1.0–5.4 µm, Stirling-cycle- cooled),
GaAs QWIP (8–9 µm, Stirling-cycle-
cooled), and microbolometer (7.5–
13.5 µm, uncooled). Measuring capability
by means of added diagnostic software.
Phoenix Family of imagers offering 320 ´ 256
and 640 ´ 512 element FPAs in 3
spectral bands: InGaAs (0.9–1.7 µm,
uncooled), InSb (2–5 µm,
Stirling-cycle-cooled) and GaAs
QWIP (8–9.2 µm, Stirling-cycle-
cooled). Measuring capability by
means of added diagnostic software.
Guangzhou SATSAT HY6700, Family of imagers offering uncooled
6800, and 6850 microbolometer 320(H) ´ 240(V) ele-
ment FPA, 8–14 µm, extensive diag-
nostic software, and wide selection of
field-interchangeable lenses.
MC600 series Family of modular units for remote
detection and process monitoring ap-
plications featuring uncooled
320(H) ´ 240(V) element micro-
bolometric FPA detectors, 8–14 µm,
extensive diagnostic software, and
field-interchangeable lenses.
140 Appendix A

Manufacturer Models Characteristics

3. Cameras, FPA, radiometric (measuring) (continued)
Guangzhou SAT 120, 160, and Family of lightweight portable units
(continued) HOTFIND featuring uncooled microbolometer
160(H) ´ 120(V) element FPA, 8–
14 µm, and extensive diagnostic soft-
ware.
HGH IRCAM82 Stirling-cycle-cooled HgCdTe 320 ´
256 element FPA, 2-color, 3–4.8 µm
or 7.7–10.3 µm.
Infrared Solu- IR InSight series Portable lightweight (4 lbs) unit fea-
tions (Fluke turing 160 ´ 120 uncooled micro-
Thermography) bolometer FPA, 8–14 µm,
incorporates spot temperature mea-
surement feature.
FlexCam R2 Portable lightweight (4 lbs) unit fea-
turing 160 ´ 120 uncooled micro-
bolometer FPA, 8–14 µm,
incorporates full temperature mea-
surement capabilities from –20 to
+100°C.
Infrared Solu- Ti series Portable lightweight (4 lbs) unit featur-
tions ing uncooled microbolometer FPA de-
tectors from 120 ´ 96 pixels to 320 ´
240 pixels, 8–14 µm, wide selection of
temperature ranges, incorporates im-
age fusion feature for blending of ther-
mal and visible images.
IRISYS IRI 1001 Very low cost, portable, battery pow-
ered using uncooled 16 ´ 16 element
pyroelectric FPA, 8–14 µm spectral
region, connects to IBM PC and in-
cludes measurement and color display
software.
IRI 1002 Multipoint radiometer module for
process control; incorporates
uncooled 16 ´ 16 element
pyroelectric FPA, 8–14 µm spectral
region, with temperature readout of
256 data points remotely.
Commercial Instrument Performance Characteristics 141

Manufacturer Models Characteristics

3. Cameras, FPA, radiometric (measuring) (continued)
IRISYS IRI 4010 Portable lightweight (2 lbs) unit fea-
(continued) turing 160 ´ 120 uncooled micro-
bolometer FPA, 8–14 µm,
incorporates spot temperature mea-
surement feature, laser pointer.
Ircon Stinger and Uncooled pyroelectric 320(H) ´
Maxline2 series 240(V) element FPA, spectral range: 5,
8, or 8–14 µm, extensive diagnostic
software, for multiple process monitor-
ing and machine vision applications.
ISG K6000 series Portable (5 lbs) units featuring un-
cooled 320 ´ 240 element bolometric
FPA detectors, 8–14 µm, temperature
range –40 to +2000°C, interchange-
able lenses, many diagnostic features.
ISG, continued ELITE, FIRECAM, Portable (3 lbs) units featuring un-
TALISMAN cooled 320 ´ 240 element bolometric
FPA detectors, 8–14 µm, temperature
range up to +1150°C, packaged for
firefighting applications.
Jenoptik VarioTHERM Stirling-cycle-cooled, 256 ´ 256 PtSi
series FPA. 3.4–7 µm, portable, battery pow-
ered, extensive diagnostic software.
VarioCAM Portable (5 lbs) unit featuring
series uncooled 640 ´ 480 element bolomet-
ric FPA detectors, 7.5–14 µm, temper-
ature range –40 to +1200°C,
interchangeable lenses, many diagnos-
tic features.
L3-Cincinnati TVS8500 Stirling-cycle-cooled 256 ´ 256 ele-
Electronics ment InSb FPA, 3–5°; 13.7 degV ´
14.6 degH TFOV, multiple tempera-
ture measurement on multiple selected
pixels, emissivity compensation.,
lightweight, and portable with
on-board LCD color monitor, accesso-
ries (also offered by AVIO).
142 Appendix A

Manufacturer Models Characteristics

3. Cameras, FPA, radiometric (measuring) (continued)
Land FTI-6 Remote-controllable module featur-
ing thermoelectrically-cooled 256 ´
256 element HgCdTe FPA detector,
3.2– 4.2 µm, for process control and
plant monitoring; extensive diagnos-
tic software.
FTI Mini and Mv Modular, compact (3 lbs) units featur-
ing uncooled 160 ´ 120 element
microbolometric FPA detectors, 7–
14 µm; for continuous process control
and plant monitoring; extensive diag-
nostic software.
Land Guide M3 Extremely small (9 oz) palm-operated
and M4 cameras featuring uncooled 160 ´ 120
element microbolometric FPA detec-
tors, 7–14 µm, and extensive diagnos-
tic capabilities; stores up to 100
images.
Cyclops PPM and Hand-held units for predictive main-
Cyclops PPM+ ER tenance applications, featuring
uncooled 320 ´ 240 or 160 ´ 120 ele-
ment BST FPA detectors, 7–14 µm;
extensive diagnostic software.
Meditherm Med200IRIS Modular unit for life science applica-
tions featuring 160 ´ 120 and 320 ´
240 element microbolometric FPA de-
tectors, 7–14 µm, temperature range
18–40°C.
Mikron M7900 series Remote process monitoring modules
for high temperatures, 300–2500°C,
operates in narrow spectral bands in
the NIR using an uncooled 320 ´ 240
element detector array.
M9100 series Remote process monitoring modules
for high temperatures, 600–4000°C,
operates in narrow spectral bands in
the NIR using an uncooled 798 ´ 494
element detector array.
Commercial Instrument Performance Characteristics 143

Manufacturer Models Characteristics

3. Cameras, FPA, radiometric (measuring) (continued)
Mikron MikroScan 7102i Uncooled microbolometer 320 ´ 240
(continued) element FPA 8–14 µm, fixed mount
camera for on-line process monitor-
ing and control.
MikroScan 7200V, Lightweight, uncooled microbolometer
7400V 320 ´ 240 element FPA 8–14 µm, bat-
tery-powered portable viewer, onboard
display and flip-up LCD option.
M7500 Process monitoring online config-
ured, uncooled microbolometer 320 ´
240 element FPA 8–14 µm, designed
for remote operation.
M7800 Ultra lightweight (2.9 lbs), uncooled
microbolometer 320 ´ 240 element
FPA 8–14 µm, battery powered porta-
ble viewer, onboard display and flip-
up LCD option onboard storage of up
to 1300 images.
MikroScan 7515 Lightweight, uncooled microbo-
and 7600PRO lometer 320 ´ 240 element FPA 8–
14 µm, battery powered portable
viewer, onboard display and flip-up
LCD option, upgrade version of the
7200 with remote control option and
analysis and report-writing software,
7515 is 30 Hz, 7600PRO is 60 Hz.
Palmer Wahl HSI3000 Wahl Hand-held, lightweight camera, un-
Heat Spy cooled 160 ´ 120 element microbo-
lometer, 8–14 µm, –10 to +250°C range,
image storage up to 1000 on card.
Quantum Focus InfraScope II Lab operated imager for microelec-
Instruments tronics applications, features liquid ni-
trogen cooled InSb FPA (256 ´ 256 or
500 ´ 500 elements), automatic
emissivity matrix measurement and
compensation, full field temperature
measurement, spatial resolution down
to 2.5 µm, 60-Hz frame rate, inter-
changeable lenses.
144 Appendix A

Manufacturer Models Characteristics

3. Cameras, FPA, radiometric (measuring) (continued)
Thermoteknix VisIR Uncooled microbolometer 160(H) ´
120(V) element FPA, portable, bat-
tery-powered, 7.5–13 µm, integral
LCD display, image storage, radio
link, extensive diagnostic software.
Thermal Wave EchoTherm EchoTherm is an NDE system built
Imaging ThermoScope II around a selection of high speed FPA
imagers. Includes flash lamp sources,
power supplies, synchronizing elec-
tronics, and analytical software for
TRIR. ThermoScope is a field-por-
table version.
Wuhan IR912 and 913 Uncooled microbolometer 320(H) ´
240(V) element FPA, portable, bat-
tery powered, 8–14 µm, 912 and 913
have fold-out LCD display, extensive
diagnostic software.
Appendix B

Manufacturers of IR Sensing
and Imaging Instruments

Manufacturer Name and Address Phone Number/Website

AIM (AEG Infrarot-Module) +49 7131 6212 46 0
49-7131-6212-20 Theresinstrasse 2, www.aim-ir.de
D-74072, Heilbronn, Germany
AVIO (Nippon Avionics see L-3 Cincinnati 03 725-1610
Electronics) www.avio.co.jp
3-1, 1-chome, Nakane, Meguro-ku Tokyo
Axsys Technologies (formerly DIOP) (603) 898-1880
282 Main Street, Salem, NH 03079 www.axsys.com
BAE Systems (603) 885 4321
95 Canal St. P.O. Box NHQ3-1109, Nashua, www.baesystems.com
NH 03061
BPC International (918) 663-7833
1535 S. Memorial Dr. Suite 117, Tulsa, www.bpcintl.com
OK 74112
CEDIP Infrared Systems SA +33 01 60 37 01 00
19 rue Georges Bidault, www.cedip-infrared.com
77183 Croissy Beaubourg, France
Compix Inc. (503) 639-8496
15824 SW Upper Boones Ferry Road www.compix.com
Lake Oswego, OR 97035
The Dickson Company (312) 543-3747,
930 S. Westwood Ave., Addison, IL 60101 (800) 757-3747
www.dicksonweb.com
Electrophysics (973) 882-0211
373 Rte 46 West, Building E, Fairfield, www.electrophysicscorp.com
NJ 07004

145
146 Appendix B

Manufacturer Name and Address Phone Number/Website

E2 Technology Corp. (part of Mikron) (805) 644-9544
4475 DuPont Ct. #9, Ventura, CA 93003 www.e2t.com
Everest Interscience Corp. (800) 422-4342
1891 North Oracle Rd., Tucson, AZ 85705 www.everestinterscience.com
Exergen Corporation (800) 422-3006
400 Pleasant St., Watertown, MA www.exergen.com
FLIR Systems, Inc. World HQ (503) 684-3771,
27700A SW Parkway Avenue, Wilsonville, (800) 322-3771
OR 97070 www.flir.com
FLIR Systems Boston and Infrared (978) 901-8000,
Training Center (800) 464-6372
16 Esquire Road, N. Billerica, MA 01862 www.flirthermography.com
Fluke Corporation (800) 283-5853
PO Box 777, Everett WA 98206-0777 www.fluke.com
Guangzhou SAT Infrared Technology Co. Ltd. +86 (0)20-82229925
10 Dongjiang Ave. Guangzhou Tech. Dev. Dist., www.sat.com.cn
China, 510730
HGH Ingenierie Systems IR +33 1 69 35 47 70
ZAC de la Sabliere 10 rue Maryse Bastie, www.hgh.fr
Igny, F-91430, France
Horiba (949) 250-4811,
17671 Armstrong Ave., Irvine, CA 92614 (800) 446-7422
www.horibalab.com
Infrared Solutions, Inc. (now Fluke (800) 760-4523
Thermography) www.infraredsolutions.com
3550 Annapolis Lane N, Suite 70, Plymouth,
MN 55447
IRCON Instruments (847) 967-5151,
7300 N. Natches Ave., Niles, IL 60714 (800) 323-7660
www.ircon.com
IRISYS (804) 763-9243 (U.S. Sales)
13614 Northwich Terrace, Midlothian, www.irisys.co.uk
VA 23112
Irtronics Instruments Inc. (914) 693-6291
132 Forest Blvd., Ardsley, NY 10502 No website listed
Manufacturers of IR Sensing and Imaging Instruments 147

Manufacturer Name and Address Phone Number/Website

ISG Thermal Systems USA, Inc. (678) 442-1234,
305 Petty Road, Lawrenceville, GA 30043 (877) 733-3473
www.isginfrared.com
JENOPTIK, GmbH +49 3641 65 39 42
Goschwitzer Strabe 25, D-07745, Jena, www.jenoptik-los.com
Germany
L-3 Communications Cincinnati Electronics (212) 697-1111
600 Third Avenue, NY, NY 10016, www.cmccinci.com
Land Instruments, Inc. (now Ametek) (215) 504-8000
10 Friends Lane, Newtown, PA 18940 www.landinstruments.net
Linear Laboratories (510) 226-0488,
42025 Osgood Rd, Fremont, CA 94539 (800) 536-0262
www.linearlabs.com
Marconi Electronic Systems (now Ericsson) (914) 592-6050,
4 Westchester Plaza, Elmsford, NY 10523 (800) 342-5338
www.marconi.com
Meditherm (252)-504-3635,
222 Lewis Road, Beaufort, NC 28516 (866) 281-5479
www.meditherm.com
Mikron Infrared, Inc. (201) 405-0900,
16 Thornton Road, Oakland, NJ 07436 (800) 631-0176
www.mikroninfrared.com
Mine Safety Appliances company (724) 766-7700,
1000 Cranbury Woods Road, Cranbury, (800) 821-3642
PA 16066 www.msanet.com
Mikron Infrared, Inc. (201) 405-0900,
16 Thornton Road, Oakland, NJ 07436 (800) 631-0176
www.mikroninfrared.com
Mine Safety Appliances company (724) 766-7700,
1000 Cranbury Woods Road, Cranbury, (800) 821-3642
PA 16066 www.msanet.com
NEC (see AVIO)
Nikon (see Pyrometer Instruments)
Omega Engineering, Inc. (203) 359-1660,
P.O. Box 4047, One Omega Dr., Stamford, (800)-848-4286
CT 06807 www.omega.com
148 Appendix B

Manufacturer Name and Address Phone Number/Website

Palmer Wahl Instrumentation Group (828) 658-3131
234 Old Weaverville Road, Asheville, (800) 421-2853
NC 28804 www.palmerwahl.com
Pyrometer Instrument Co. Inc. (609) 443-5522
92 North Main Street Bldg 18-D, Windsor, www.pyrometer.com
NJ 08561
Quantum Focus Instruments Corp. (760) 599-1122
990 Park Center Drive Suite D, Vista, www.quantumfocus.com
California 92083
Quantum Logic Corp. (203) 226-4135
Box 191, Westport, CT 06881 www.quantumlogic.com
Raytek, Inc. (a Fluke Company) (831) 458-1110,
1201 Shaffer Rd., Santa Cruz, CA 95060 (800) 227-8074
www.raytek.com
RedShift Systems, Inc. (781) 672-2662
1601 Trapelo Rd. Ste 214, Waltham, MA 02451 www.redshiftsystems.com
Telatemp Corp. (714) 879-2901,
PO Box 5160, 351 S. Raymond, Fullerton, (800) 321-5160
CA 92635 www.teletemp.com
Thermal Wave Imaging, Inc. (248) 414-3730
845 Livernois St., Ferndale, MI 48220 www.thermalwave.com
Thermoteknix Systems, Ltd., Teknix House +44 1223-204-000
2 Pembroke Ave., Waterbeach Cambridge, www.thermoteknix.com
UK CB5 9QR
US Infrared (see BPC International)
Williamson Corp. (978) 369-9607
70 Domino Dr. Box 1270, Concord, MA 01742 www.williamsonir.com
Wuhan Guide Electronic Industrial Co. Ltd. +86 27-87659277
Hongshan Chuangye Ctr BldgLuoyu Rd. www.wuhanguide.com
No. 424
Wuhan, China
Appendix C

Table of Generic Normal

Emissivities of Materials

Reprinted from Thermographic Inspection of Electrical Installations, Agema In-

frared Systems (now FLIR), publication 556 556 776 (1984). Spectral bands are as
indicated.

NOTE: Where temperature is not indicated, it is assumed to be 30°C.

SW = 2–5.6 µm; LW = 6.5–20 µm.

Wavelength Temperature
Material Emissivity
(micrometers) (°C)
Alumina brick SW 17 0.68
Aluminum, heavily SW 17 0.83–0.94
weathered
Aluminum foil 3 0.09
Aluminum foil (bright) 3 0.04
Aluminum disk, 3 0.28
roughened
Asbestos slate (wallboard) 3 0.96
Brick, common SW 17 0.81–0.86
Brick, facing, red SW 0.92
Brick, facing, yellow SW 0.92
Brick, masonry SW 0.72
Brick, red 5 0 0.94
Brick, waterproof SW 17 0.9
Chipboard, untreated SW 0.9
Concrete, dry 5 36 0.95
Concrete, rough SW 17 0.92–0.97
Copper, polished, annealed 10 0.01

149
150 Appendix C

Wavelength Temperature
Material Emissivity
(micrometers) (°C)
Fibre board (hard), SW 0.85
untreated
Fibre board (porous), SW 0.85
untreated
Filler, white SW 0.88
Firebrick SW 17 0.68
Formica LW 27 0.937
Frozen soil LW 0.93
Glass, chemical ware 5 35 0.97
(partly transparent)
Granite, natural surface 5 36 0.96
Gravel LW 0.28
Hardwood, across grain SW 17 0.82
Hardwood, along grain SW 17 0.68–0.73
Hessian Fabric, green SW 0.88
Hessian Fabric, uncolored SW 0.87
Iron, heavily rusted SW 17 0.91–0.96
Limestone, natural surface 5 36 0.96
Mortar SW 17 0.87
Mortar, dry 5 36 0.94
P.V.C. SW 17 0.91–0.93
Paint (by manufacturer)
Broma Alkyd enamel 3 40 0.98
102 gold leaf
Broma Alkyd enamel 3 0.95
113 light blue
Chromatone stabilized 3 25 0.26
silver finish – Aluma- 10 0.31
tone Corp.
Krylon flat black 1502 3 50 0.95
Krylon flat white 3 40 0.99
Krylon ultra-flat black 5 36 0.97
Table of Generic Normal Emissivities of Materials 151

Wavelength Temperature
Material Emissivity
(micrometers) (°C)
Paint (by manufacturer)
(continued)
3M black velvet coat- 3 40 >0.99
ing 9560 series optical
black
Oil SW 17 0.87
black flat SW 0.94
black gloss SW 0.92
gray flat SW 0.97
gray gloss SW 0.96
Plastic, black SW 0.95
Plastic, white SW 0.84
Paper, cardboard box 5 0.81
Paper, white SW 17 0.68
Perspex, plexiglass SW 17 0.86
Plaster Pipes, glazed SW 17 0.83
Plaster SW 17 0.86–0.9
Plasterboard, SW 0.9
untreated
Plastic, acrylic, clear 5 36 0.94
Plastic paper, red SW 0.94
Plywood SW 17 0.83–0.98
Plywood, commercial, 5 36 0.82
smooth finish, dry
Plywood, untreated SW 0.83
Polypropylene SW 17 0.97
Redwood (wrought), SW 0.83
untreated
Redwood (unwrought), SW 0.84
untreated
Rendering, gray SW 0.92
152 Appendix C

Wavelength Temperature
Material Emissivity
(micrometers) (°C)
Roofing Metal
Azure blue, smooth SW 0 0.54
Azure blue, textured SW 0 0.51
Burnished copper, SW 0 0.54
smooth
Burnished copper, SW 0 0.56
textured
Dark bronze, textured SW 0 0.7
Mansard brown, smooth SW 0 0.58
Matte black, smooth SW 0 0.73
Roman bronze, smooth SW 0 0.69
Slate gray, smooth SW 0 0.64
Stone white, smooth SW 0 0.57
Terra Cotta, smooth SW 0 0.61
Shingles – asphalt (sm. ce-
ramic-coated rock granules)
Adobe SW 0 0.77
Black SW 0 0.83
Bright Red SW 0 0.96
Chestnut Brown SW 0 0.67
Colonial Green SW 0 0.83
Dawn Mist SW 0 0.76
Desert Tan SW 0 0.74
Frost Blende SW 0 0.76
Meadow Green SW 0 0.78
Noire Black SW 0 0.90
Sea Green SW 0 0.83
Shadow Gray SW 0 0.81
Slate Blende SW 0 0.65
Snow White SW 0 0.81
Wedgewood Blue SW 0 0.75
Table of Generic Normal Emissivities of Materials 153

Wavelength Temperature
Material Emissivity
(micrometers) (°C)
Shingles – asphalt (sm. ce-
ramic-coated rock gran-
ules) (continued)
Wood Blende SW 0 0.75
Average SW 0 0.89
Fiberglass – asphalt sm
ceramic- coated rock
granules
Frost Blende SW 0 0.83
Mahogany SW 0 0.84
Meadow Mist SW 0 0.98
Noire Black SW 0 0.93
Snow White SW 0 0.74
Wood Blende SW 0 0.81
Average SW 0 0.86
Solid vinyl
Autumn gold, textured SW 0 0.79
Butternut beige, SW 0 0.80
textured
Lexington green, SW 0 0.86
textured
Oyster white, textured SW 0 0.88
Quaker gray, textured SW 0 0.89
Sunshine yellow, SW 0 0.75
textured
White, smooth SW 0 0.93
Average SW 0 0.94
Styrofoam, insulation 5 37 0.60
Tape, electrical, insulating, 5 35 0.97
black
Tape, masking 5 36 0.92
Tile, floor, asbestos 5 35 0.94
154 Appendix C

Wavelength Temperature
Material Emissivity
(micrometers) (°C)
Tile, glazed SW 17 0.94
Varnish, flat SW 0.93
Wallpaper (slight pattern) SW 0.85
It. gray
Wallpaper (slight pattern) SW 0.90
red
Wood, paneling, light 5 36 0.87
finish
Wood, polished spruce, 5 36 0.86
gray
Appendix D

A Glossary of Terms for the

Infrared Thermographer

(Reprinted courtesy of Honeyhill Technical Company—updated 8/28/06)

The following are explanations and definitions of terms commonly encountered by

the infrared thermographer. Many of these terms have multiple definitions and the
one provided is the one most applicable to infrared thermography. NOTE: In some
cases, the “textbook” definition of a term is replaced by one more explicitly dealing
with the practice of infrared thermography.

Absolute zero – The temperature that is zero on the Kelvin or Rankine temperature
scales, the temperature at which no molecular motion takes place in a material.
Absorptivity, symbol a (absorptance) – The proportion (as a fraction of 1) of the
radiant energy impinging on a material’s surface that is absorbed into the mate-
rial. For a black body, this is unity (1.0). Technically, absorptivity is the internal
absorptance per unit path length. In thermography, the two terms are often used
interchangeably.
(Note: same symbol as diffusivity, may be confusing).
Accuracy (of measurement) – The maximum deviation, expressed in % of scale or
in degrees C or F, that the reading of an instrument will deviate from an accept-
able standard reference, normally traceable to NIST (National Institute for
Standards and Technology).
Ambient operating range – Range of ambient temperatures over which an instru-
ment is designed to operate within published performance specifications.
Ambient temperature – Temperature of the air in the vicinity of the target (target
ambient) or the instrument (instrument ambient).
Ambient temperature compensation – Correction built into an instrument to pro-
vide automatic compensation in the measurement for variations in instrument
ambient temperature.
Apparent temperature – The target surface temperature indicated by an infrared
point sensor, line scanner or imager.
Anomaly – An irregularity, such as a thermal variation on an otherwise isothermal
surface; any indication that deviates from what is expected.
Artifact – A product of artificial character due to extraneous agency; an error
caused by an uncompensated anomaly. In thermography, for example, an

155
156 Appendix D

emissivity artifact simulates a change in surface temperature but is not a real

change.
Atmospheric windows (infrared) – The spectral intervals within the infrared
spectrum in which the atmosphere transmits radiant energy well (atmospheric
absorption is a minimum). These are roughly defined as 2–5 µm and 8–14 µm.
Background temperature, instrument – Apparent ambient temperature of the
scene behind and surrounding the instrument, as viewed from the target. The re-
flection of this background may appear in the image and affect the temperature
measurement. Most quantitative thermal sensing and imaging instruments pro-
vide a means for correcting measurements for this reflection. (See figure A-1.).
Background temperature, target – Apparent ambient temperature of the scene
behind and surrounding the target, as viewed from the instrument. When the
FOV of a point sensing instrument is larger than the target, the target back-
ground temperature will affect the instrument reading. (See figure A-1.).
Blackbody, blackbody radiator – A perfect emitter; an object that absorbs all the
radiant energy impinging on it and reflects and transmits none. A surface with
emissivity of unity (1.0) at all wavelengths.
Bolometer, infrared – A type of thermal infrared detector.
Celsius (Centigrade) – A temperature scale based on 0°C as the freezing point of
water and 100°C as the boiling point of water at standard atmospheric pressure;
a relative scale related to the Kelvin scale [0°C = 273.12K; 1°C(DT) = 1K(DT)].
Calibration – Checking and/or adjusting an instrument such that its readings agree
with a standard.
Calibration check – A routine check of an instrument against a reference to ensure
that the instrument has not deviated from calibration since its last use.
Calibration accuracy – The accuracy to which a calibration is performed, usually
based on the accuracy and sensitivity of the instruments and references used in
the calibration.
Calibration source, infrared – A blackbody or other target of known temperature
and effective emissivity used as a calibration reference.
Capacitance, thermal – This term is used to describe heat capacity in terms of an
electrical analog, where loss of heat is analogous to loss of charge on a capaci-
tor. Structures with high thermal capacitance change temperature more slowly
than those with low thermal capacitance.

Figure A-1 Target and instrument background.

A Glossary of Terms for the Infrared Thermographer 157

Capacity, heat – The heat capacity of a material, or a structure, describes its ability
to store heat. It is the product of the specific heat (cr) and the density (r) of the
material. This means that denser materials generally will have higher heat ca-
pacities than porous materials.
Color – A term sometimes used to define wavelength or spectral interval, as in
two-color radiometry (meaning a method that measures in two spectral inter-
vals); also used conventionally (visual color) as a means of displaying a ther-
mal image, as in color thermogram.
Colored body – See nongray body.
Conduction – The only mode of heat flow in solids, but can also take place in liq-
uids and gases. It occurs as the result of atomic vibrations (in solids) and molec-
ular collisions (in liquids and gases) whereby energy is transferred from
locations of higher temperature to locations of lower temperature.
Conductivity, thermal (symbol, k) – a material property defining the relative ca-
pability to carry heat by conduction in a static temperature gradient. Conductiv-
ity varies slightly with temperature in solids and liquids and with temperature
and pressure in gases. It is high for metals (copper has a k of 380 W/m-°C) and
low for porous materials (concrete has a k of 1.0) and gases.
Convection – The form of heat transfer that takes place in a moving medium and is
almost always associated with transfer between a solid (surface) and a moving
fluid (such as air), whereby energy is transferred from higher temperature sites
to lower temperature sites.
Detector, infrared – A transducer element that converts incoming radiant energy
impinging on its sensitive surface to a useful electrical signal.
Diffuse reflector – A surface that reflects a portion of the incident radiation in such
a manner that the reflected radiation is equal in all directions. A mirror is not a
diffuse reflector.
Diffusivity, thermal (symbol, a) – The ratio of conductivity (k) to the product of
density, (r) and specific heat (cr) [a = k/rcr cm2 sec 1 ]. The ability of a mate-
rial to distribute thermal energy after a change in heat input. A body with a high
diffusivity will reach a uniform temperature distribution faster than a body with
lower diffusivity.
(Note: same symbol as absorptivity, may be confusing.)
D* (detectivity star) – Sensitivity figure of merit of an infrared detec-
tor—detectivity is expressed inversely so that higher D*s indicate better per-
formance; taken at specific test conditions of chopping frequency and
information bandwidth and displayed as a function of spectral wavelength.
Display resolution, thermal – The precision with which an instrument displays its
assigned measurement parameter (temperature), usually expressed in degrees,
tenths of degrees, hundredths of degrees, etc.
Effective emissivity (symbol, e*) The measured emissivity value of a particular
target surface under existing measurement conditions (rather than the generic
tabulated value for the surface material) that can be used to correct a specific
158 Appendix D

measuring instrument to provide a correct temperature measurement (also

called emittance, but emittance is less preferable because it has been used to de-
scribe radiant exitance).
Effusivity, thermal (symbol, e) – A measure of the resistance of a material to tem-
perature change
[e = krcr cal cm2 °C 1 sec1/2] where:
k = thermal conductivity
r = bulk density
cr = specific heat
Emissivity (symbol, e) – The ratio of a target surface’s radiance to that of a
blackbody at the same temperature, viewed from the same angle and over the
same spectral interval; a generic look-up value for a material. Values range
from zero to 1.0.
EMI/RFI noise – Disturbances to electrical signals caused by electromagnetic in-
terference (EMI) or radio frequency interference (RFI). In thermography, this
may cause noise patterns to appear on the display.
Environmental rating – A rating given an operating unit (typically an electrical or
mechanical enclosure) to indicate the limits of the environmental conditions
under which the unit will function reliably and within published performance
specifications.
Exitance, radiant (also called radiosity) – Total infrared energy (radiant flux) leav-
ing a target surface. This is composed of radiated, reflected and transmitted com-
ponents. Only the radiated component is related to target surface temperature.
Fahrenheit – A temperature scale based on 32°F as the freezing point of water and
212°F as the boiling point of water at standard atmospheric pressure; a relative
scale related to the Rankine scale
[0°F = 459.67R; 1°F (DT) = 1R (DT)].
Field of view (FOV) – The angular subtense (expressed in angular degrees or radi-
ans per side if rectangular, and angular degrees or radians if circular) over
which an instrument will integrate all incoming radiant energy. In a radiation
thermometer this defines the target spot size; in a scanner or imager this defines
the scan angle or picture size or total field of view (TFOV).
Fiber optic, infrared – A flexible fiber made of a material that transmits infrared
energy, used for making noncontact temperature measurements when there is
not a direct line of sight between the instrument and the target.
Filter, spectral – An optical element, usually transmissive) used to restrict the
spectral band of energy received by the detector.
Focal plane array (FPA) – A linear or two-dimensional matrix of detector ele-
ments, typically used at the focal plane of an instrument. In thermography, rect-
angular FPAs are used in «staring» (non-scanning) infrared imagers. These are
called IRFPA imagers.
Focal point – The point at which the instrument optics image the infrared detector
at the target plane. In a radiation thermometer, this is where the spot size is the
A Glossary of Terms for the Infrared Thermographer 159

smallest. In a scanner or imager, this is where the instantaneous field of view

(IFOV) is smallest.
Foreground temperature – see instrument ambient background. Temperature of
the scene behind and surrounding the instrument, as viewed from the target.
(See figure A-1.)
Frame repetition rate – The time it takes an infrared imager to scan (update) every
thermogram picture element (pixel); in frames per second.
Full scale – The span between the minimum value and the maximum value that any
instrument is capable of measuring. In a thermometer this would be the span
between the highest and lowest temperature that can be measured.
Gray body – A radiating object whose emissivity is a constant value less than unity
(1.0) over a specific spectral range.
Hertz (Hz) – A unit of measurement of signal frequency; 1Hz = 1 cycle per second.
Hole response function, HRF – A measure of the measurement spatial resolution
(IFOVmeas or MFOV) of a focal plane array-based infrared camera.
Image, infrared – See Thermogram.
Imager, infrared – An infrared instrument that collects the infrared radiant energy
from a target surface and produces an image in monochrome (black-and-white)
or color, where the gray shades or color hues correspond respectively to target
exitance.
Image display tone – Gray shade or color hue on a thermogram.
Image fusion – The intelligent, fully registered, combination of multi-modality
sensor imagery for the purpose of providing an enhanced single view of a scene
with extended information content.
Image fusion, thermal – The fully-registered combination of a thermal image with
another mode of image for the purpose of providing an enhanced single view of
a scene with extended information content.
Image processing, thermal – Analysis of thermal images, usually by computer;
enhancing the image to prepare it for computer or visual analysis. In the case of
an infrared image or thermogram this could include temperature scaling, spot
temperature measurements, thermal profiles, image manipulation, subtraction
and storage.
Imaging radiometer – An infrared thermal imager that provides quantitative ther-
mal images.
Indium Antimonide (InSb) – A material from which fast, sensitive photodetectors
used in infrared sensors, scanners and imagers are made. Such detectors usually
requiring cooling while in operation.
Inertia, thermal – See thermal effusivity.
Infrared (IR) – The infrared spectrum is loosely defined as that portion of the elec-
tromagnetic continuum extending from the red visible (0.75 µm) to about
1000 µm. Because of instrument design considerations and the infrared trans-
mission characteristics of the atmosphere, however, most infrared measure-
ments are made between 0.75 and 20 µm.
160 Appendix D

Infrared (IR) camera – Any infrared imaging instrument that produces a thermo-
gram.
Infrared fiber optic – A fiber optic that transmits in the infrared region.
Infrared focal plane array (IRFPA) – A linear or two-dimensional matrix of indi-
vidual infrared detector elements, typically used as a detector in an infrared im-
aging instrument.
IRFPA imager or camera – An infrared imaging instrument that incorporates a
two-dimensional IRFPA (focal plane array) and produces a thermogram with-
out mechanical scanning.
Infrared radiation thermometer – An instrument that converts incoming infrared
radiant energy from a spot on a target surface to a measurement value that can
be related to the temperature of that spot.
Infrared thermal imager – An instrument or system that converts incoming infra-
red radiant energy from a target surface to a thermal map, or thermogram, on
which color hues or gray shades can be related to the temperature distribution
on that surface.
Infrared viewing window – A device incorporating a visibly transparent window
that is also transparent in the infrared.
Instantaneous field of view (IFOV) – The angular subtense (expressed in angular
degrees or radians per side if rectangular, and angular degrees or radians if
round) over which an instrument will integrate all incoming radiant energy; the
projection of the detector at the target plane. In a radiation thermometer this de-
fines the target spot size; in a line scanner or imager it represents one resolution
element in a scan line or a thermogram and is a measure of spatial resolution.
Isotherm – A pattern superimposed on a thermogram or on a line scan that includes
or highlights all points that have the same apparent temperature.
Kelvin – Absolute temperature scale related to the Celsius (or Centigrade) relative
scale. The Kelvin unit is equal to 1°C; 0 Kelvins = –273.16°C; the degree sign
and the word “degrees” are not used in describing Kelvin temperatures.
Laser pyrometer – An infrared radiation thermometer that projects a laser beam to
the target, uses the reflected laser energy to compute target effective emissivity
and automatically computes target temperature (assuming that the target is a
diffuse reflector)—not to be confused with laser-aided aiming devices on some
radiation thermometers.
Line scan rate – The number of target lines scanned by an infrared scanner or
imager in one second.
Line scanner, infrared – An instrument that scans an infrared field of view along a
straight line at the target plane in order to collect infrared radiant energy from a line
on the target surface, usually done by incorporating one scanning element within
the instrument. If the target (such as a sheet or web process) moves at a fixed rate
normal to the line scan direction, the result can be displayed as a thermogram.
LWIR – An acronym for long wave infrared, describing the long wave operating
region of certain infrared instruments, from about 7 to 14 µm.
A Glossary of Terms for the Infrared Thermographer 161

Measurement spatial resolution, IFOVmeas or MFOV – The smallest target spot

size on which an infrared camera can produce a measurement, expressed in terms
of angular subtense (mrad). The slit response function (SRF) test is used to mea-
sure IFOVmeas in optomechanically scanned imagers. The hole response function
(HRF) test is used to measure IFOVmeas in optomechanically scanned imagers.
Medium, transmitting medium – The composition of the measurement path be-
tween a target surface and the measuring instrument through which the radiant
energy propagates. This can be vacuum, gaseous (such as air), solid, liquid or
any combination of these.
Mercury cadmium telluride MCT (HgCdTe) – A material used for fast, sensitive
infrared photodetectors used in infrared sensors, scanners and imagers and re-
quiring cooled operation.
Micron (micrometer) – 1 millionth of a meter; a unit used to express wavelength
in the infrared; symbol is µm or µ (µm is preferred).
Milliradian (mrad) – One thousandth of a radian (1 radian = 180°/p); a unit used to
express instrument angular field of view; an angle whose tangent is equal to
0.001; (1mrad = 0.05729578°).
Minimum resolvable temperature (difference), MRT(D) – Thermal resolution;
thermal sensitivity—the smallest temperature difference that an instrument can
clearly distinguish out of the noise, taking into account characteristics of the
display and the subjective interpretation of the operator.
Modulation – In general, the changes in one wave train caused by another; in ther-
mal scanning and imaging, image luminant contrast; (Lmax – Lmin)/(Lmax + Lmin).
Modulation Transfer Function (MTF) – A measure of the ability of an imaging
system to reproduce the image of a target. A formalized procedure is used to
measure MTF. It assesses the spatial resolution of a scanning or imaging sys-
tem as a function of distance to the target.
MWIR – An acronym for mid wave infrared, describing the mid wave operating
region of certain infrared instruments, from about 2 to 5 µm.
Noise equivalent temperature (difference), NET(D) – The temperature differ-
ence that is just equal to the noise signal; a measure of thermal resolution, but
not taking into account characteristics of the display and the subjective inter-
pretation of the operator.
NIR – An acronym for near infrared, describing the near infrared operating region
of certain infrared instruments, from about 0.7 to 1.9 µm, also referred to as
short wave infrared, SWIR.
NIST, NIST traceability – The National Institute of Standards and Technology
(formerly NBS). Traceability to NIST is a means of ensuring that a reference
standard remains valid and its calibration remains current.
Nongray body – A radiating object that does not have a spectral radiation distribu-
tion similar to a black body and may be partly transparent to infrared (transmits
infrared energy at certain wavelengths); also called a “colored body” or “real
body”. Glass and plastic films are examples of nongray bodies.
162 Appendix D

Objective, objective lens – The primary lens of an optical system, on an infrared

instrument, usually the interchangeable lens that defines the total field of view.
Opaque – Impervious to radiant energy. In thermography an opaque material is one
that does not transmit thermal infrared energy. (t = 0)
Optical element, infrared – Any element that collects, transmits, restricts, re-
fracts or reflects infrared energy as part of an infrared sensing or imaging in-
strument.
Peak hold – A feature of an instrument whereby an output signal is maintained at
the peak instantaneous measurement for a specified duration.
Photodetector (photon detector) – A type of infrared detector that has fast re-
sponse, (on the order of microseconds) limited spectral response and usually
requires cooled operation; photodetectors are used in infrared radiation ther-
mometers, scanners and imagers.
Pulsed thermography – A term used to describe an active technique for infrared
nondestructive material testing, in which the sample is stimulated with pulses
of thermal energy, and where the time-based returned thermal images are pro-
cessed to determine flaw depth and severity; also called “pulse-stimulated im-
aging” and “thermal wave imaging.”
Pyroelectric detector – A type of thermal infrared detector that acts as a current
source with its output proportional to the rate of change of its temperature.
Pyroelectric vidicon (PEV) also called a pyrovidicon – a video camera tube with
its receiving element fabricated of pyroelectric material and sensitive to wave-
lengths from about 2 to 20 µm; used in infrared thermal viewers.
Pyrometer – Any instrument used for temperature measurement. A radiation or
brightness pyrometer measures visible energy and relates it to brightness or
color temperature. An infrared pyrometer measures infrared radiation and re-
lates it to target surface temperature.
QWIP – Quantum Well Infrared Photodetector; a fast, sensitive infrared photo-
detector used in infrared sensors, scanners and imagers and requiring cooled
operation. QWIPs are usually built on InGaAs (indium gallium arsenide) sub-
strates and their spectral operating regions can be tuned, during manufacture, to
narrow bands from the MWIR through the LWIR.
Radian – An angle equal to 180°/p or 57.29578 angular degrees.
Radiation, thermal – The mode of heat flow that occurs by emission and absorp-
tion of electromagnetic radiation, propagating at the speed of light and, unlike
conductive and convective heat flow, capable of propagating across a vacuum;
the form of heat transfer that allows infrared thermography to work since IR en-
ergy travels from the target to the detector by radiation.
Radiation reference source – A blackbody or other target of known temperature
and effective emissivity used as a reference to obtain optimum measurement
accuracy, ideally, traceable to NIST.
Radiation thermometer – See Infrared radiation thermometer.
Radiosity – See exitance, radiant.
A Glossary of Terms for the Infrared Thermographer 163

Rankine – Absolute temperature scale related to the Fahrenheit relative scale. The
Rankine unit is equal to 1°F; 0 Rankines = –459.72°F; the degree sign and the
word “degrees” are not used in describing Rankine temperatures.
Ratio pyrometer – An infrared thermometer that uses the ratio of incoming infra-
red radiant energy at two narrowly separated wavelengths to determine a tar-
get’s temperature independent of target emissivity. This assumes “Graybody”
conditions and is normally limited to relatively hot targets (above about
300°F).
Reference junction – In a thermocouple, the junction of the dissimilar metals that
is not the measurement junction. This is normally maintained at a constant ref-
erence temperature.
Reflectivity (symbol, r), (reflectance) – The ratio of the total energy reflected
from a surface to total incident on that surface; (r = 1 – e – t); for a perfect
mirror this approaches 1.0; for a black body the reflectivity is 0. Technically, re-
flectivity is the ratio of the intensity of the reflected radiation to the total radia-
tion and reflectance is the ratio of the reflected flux to the incident flux. In
thermography, the two terms are often used interchangeably.
Relative humidity – The ratio (in percent) of the water vapor content in the air to
the maximum content possible at that temperature and pressure.
Repeatability – The capability of an instrument to exactly repeat a reading on an
unvarying target over a short or long term time interval. For thermal measure-
ments, expressed in ± degrees or a percentage of full scale.
Resistance, thermal (symbol, R) – A measure of a material’s resistance to the flow
of thermal energy, inversely proportional to its thermal conductivity, k. (1/R = k)
Response time – The time it takes for an instrument output signal or display to re-
spond to a temperature step change at the target; expressed in seconds. (typi-
cally, to 95% of the final value, and approximately equal to 5 time constants)
RTD – Resistance temperature device; a sensor that measures temperature by a
change in resistance as a function of temperature.
Sample hold – A feature of an instrument whereby an output signal is maintained at
an instantaneous measurement value for a specified duration after a trigger or
until an external reset is applied.
Scan angle – For a line scanner, the total angular scan possible at the target plane,
typically 90°.
Scan position accuracy – For a line scanner, the precision with which instanta-
neous position along the scan line can be set or measured.
Sector – For a line scanner, a portion of the total scan angle over which measure-
ment is made at the target plane.
Seeback effect – The phenomenon that explains the operation of thermocouples;
that in a closed electrical circuit made up of two junctions of dissimilar metal
conductors, a DC current will flow as long as the two junctions are at different
temperatures. The phenomenon is reversible; if the temperatures at the two
junctions are reversed, the direction of current flow reverses.
164 Appendix D

Sensitivity – See MRTD, Minimum resolvable temperature difference.

Setpoint – Any temperature setting at which an activating signal or closure can be
preset so that, when the measured temperature reaches the setpoint, a control
signal, pulse or relay closure is generated.
Shock – A sudden application of force, for a specific time duration; also the tempo-
rary or permanent damage to a system as a result of a shock
Signal processing – Manipulation of temperature signal or image data for purposes of
enhancing or controlling a process. Examples for infrared radiation thermometers
are peak hold, valley hold, sample hold and averaging. Examples for scanners and
imagers are usually referred to as “image processing” and include isotherm en-
hancement, image averaging, alignment, image subtraction and image filtering.
Slit response function, SRF – A measure of the measurement spatial resolution
(IFOVmeas or MFOV) of an optomechanically-scanned infrared camera.
Spatial resolution – The spot size in terms of working distance (containing 95% of
the radiant energy, according to common usage). In an infrared radiation ther-
mometer this is expressed in angular degrees, milliradians or as a ratio (D/d) of
the target spot size to the working distance. In infrared cameras it is most often
expressed in milliradians.
Spectral response – The spectral wavelength interval over which an instrument or
sensor responds to infrared radiant energy, expressed in micrometers
(µm)—also, the relative manner (spectral response curve) in which it responds
over that interval.
Specular reflector – A smooth reflecting surface that reflects all incident radiant
energy at an angle complementary (equal around the normal) to the angle of in-
cidence. A mirror is an example of a specular reflector.
Spot – The instantaneous size (diameter unless otherwise specified) of the area at
the target plane that is being measured by the instrument. In infrared thermom-
etry, this is specified by most manufacturers to contain 95% of the radiant en-
ergy of an infinitely large target of the same temperature and emissivity.
Storage operating range – The temperature extremes over which an instrument
can be stored and, subsequently, operate within published performance specifi-
cations.
Subtense, angular – The angular diameter of an optical system or subsystem, ex-
pressed in angular degrees or milliradians. In thermography, the angle over
which a sensing instrument collects radiant energy.
SWIR – An acronym for short wave infrared, describing the short wave infrared
operating region of certain infrared instruments, from about 0.7 to 1.9 µm, also
referred to as near infrared, NIR.
Target – The object surface to be measured or imaged.
Temperature – A measure of the thermal energy contained by an object; the degree
of hotness or coldness of an object measurable by any of a number or relative
scales. Heat is defined as thermal energy in transit, and flows from objects of
higher temperature to objects of lower temperature.
A Glossary of Terms for the Infrared Thermographer 165

Temperature conversion – Converting from one temperature scale to another; the

relationships are:
C temperature = (F temperature – 32)(5/9)
F temperature = 9/5C temperature + 32
1°C(DT) = 5/9°F(DT)
0°C = 273.12 Kelvins; 0°F = 459.67 Rankines
Temperature measurement drift – A reading change (error), with time, of a target
with nonvarying temperature, which may be caused by a combination of ambi-
ent changes, line voltage changes and instrument characteristics.
Temperature resolution – See MRTD, minimum resolvable temperature differ-
ence.
Thermal detector, infrared – A type of infrared detector that changes electrical
characteristics as a function of temperature; typically, thermal detectors have
slow response, (on the order of milliseconds) broad spectral response and usu-
ally operate at room temperature; thermal detectors are commonly used in IR
radiation thermometers and in some imagers.
Thermal viewer – A nonmeasuring thermal imager that produces qualitative ther-
mal images related to thermal radiant distribution over the target surface.
Thermal wave imaging – A term used to describe an active technique for infrared
nondestructive material testing, in which the sample is stimulated with pulses
of thermal energy, and where the time-based returned thermal images are pro-
cessed to determine flaw depth and severity; also called “pulse-stimulated im-
aging” and “pulsed thermography.”
Thermistor – A temperature detector, usually a semiconductor, whose resistivity
decreases predictably with increasing temperature.
Thermistor bolometer, infrared – A thermistor so configured as to collect radiant
infrared energy; a type of thermal infrared detector.
Thermocouple – A device for measuring temperature based on the fact that oppo-
site junctions between certain dissimilar metals develop an electrical potential
when placed at different temperatures; typical thermocouple types are:
J iron/constantan
K chromel/alumel
T copper/constantan
E chromel/constantan
R platinum/platinum-30% rhodium
S platinum/platinum-10% rhodium
B platinum-6% rhodium/platinum-30% rhodium
G tungsten/tungsten-26% rhenium
C tungsten-5% rhenium/tungsten-26% rhenium
D tungsten-3% rhenium/tungsten-25% rhenium
Thermogram – A thermal map or image of a target where the gray tones or color
hues correspond to the distribution of infrared thermal radiant energy over the
surface of the target (qualitative thermogram); when correctly processed and
166 Appendix D

corrected, a graphic representation of surface’s apparent temperature distribu-

tion (quantitative thermogram).
Thermograph – Another word used to describe an infrared thermal imager.
Thermographer – A practitioner of thermography.
Thermographic Signal Reconstruction (TSR) – A signal processing technique
for reconstructing and improving time-resolved thermal images, used in pulsed
thermography material testing.
Thermography – The process involved in producing thermograms.
Thermology – A term sometimes used to describe thermography in medical appli-
cations.
Thermometer – Any device used for measuring temperature.
Thermopile – A device constructed by the arrangement of thermocouples in series
to add the thermoelectric voltage. A radiation thermopile is a thermopile with
junctions so arranged as to collect infrared radiant energy from a target, a type
of thermal infrared detector.
Time constant – The time it takes for any sensing element to respond to 63.2% of a
step change at the target being sensed. In infrared sensing and thermography,
the time constant of a detector is a limiting factor in instrument performance, as
it relates to response time.
Total field of view (TFOV) – In imagers, the total solid angle scanned, usually rect-
angular in cross section.
Transducer – Any device that can convert energy from one form to another. In
thermography, an IR detector is a transducer that converts infrared radiant en-
ergy to some useful electrical quantity.
Transfer calibration – A technique for correcting a temperature measurement or a
thermogram for various errors by placing a radiation reference standard adja-
cent to the target.
Transfer standard – A precision radiometric measurement instrument with NIST
traceable calibration used to calibrate radiation reference sources.
Transmissivity, (symbol t) (transmittance) – The proportion of infrared radiant
energy impinging on an object’s surface, for any given spectral interval, that is
transmitted through the object. (t = 1 – e – r) For a black body, transmis-
sivity = 0. Transmissivity is the internal transmittance per unit thickness of a
nondiffusing material.
Two-color pyrometer – See Ratio pyrometer.
Unity – One (1.0).
Valley hold – A feature of an instrument whereby an output signal is maintained at
the lowest instantaneous measurement for a specified duration; opposite of
peak-hold.
Working distance – The distance from the target to the instrument, usually to the
primary optic.
Zone – In line scanners, a scanned area created by the transverse linear motion of
the product or process under a measurement sector of the scanner.
 Herbert Kaplan received a BSEE degree from Brook-
lyn Polytechnic Institute in 1952. He has been in-
volved in photonics applications engineering,
specifically in the field of infrared sensing and imag-
ing, since 1963, when he joined Barnes Engineering
Company. In 1980 he formed Honeyhill Technical
Company, where he is presently the general manager.
An active infrared thermographer, Kaplan has
conducted measurement programs for a wide range of
clients including the U.S. Army, the U.S. Air Force,
NASA/JPL, and the Electric Power Research Institute
(EPRI). From 2000–2003 he served as co-chair and author liaison for the annual
“InfraMation” series of thermographers’ conferences co-sponsored by FLIR Sys-
tems and FLIR’s Infrared Training Center.
An SPIE Fellow (1990), Kaplan has authored numerous publications, including
Practical Applications of Infrared Thermal Sensing and Imaging Equipment, Second
Edition (SPIE Tutorial Text vol. TT34, 1999), the ASNT’s Thermal/Infrared Testing
Level III Study Guide (2001), a chapter on infrared thermography for McGraw-Hill’s
Electronic Failure Analysis Handbook (1997), several chapters for the ASNT’s Ther-
mal/Infrared Method Handbook (2001), and the Nuclear Maintenance Applications
Center’s Infrared Thermography Guide, Rev. 3 (2002) for EPRI.
Kaplan is a member and past chairman of SPIE’s Thermosense Working Group
and past chairman of the Thermosense conference. He has served on the edito-
rial review boards of Elsevier’s journal, Infrared Science and Technology, and of
Photonics Spectra magazine. For 12 years he was also a contributing editor for
Photonics Spectra, where he prepared the monthly “Photonics at Work” column
and other feature articles.
Kaplan currently resides in Boynton Beach, Florida.