This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what

changes have been made to the previous version. Because

it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.

Designation: E2847 − 13´1 E2847 − 14

Standard Test Method for

Calibration and Accuracy Verification of Wideband Infrared
Thermometers1
This standard is issued under the fixed designation E2847; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.

ε1 NOTE—Title corrected editorially in September 2013.

1. Scope
1.1 This test method covers electronic instruments intended for measurement of temperature by detecting the intensity of
thermal radiation exchanged between the subject of measurement and the sensor.
1.2 The devices covered by this test method are referred to as infrared thermometers in this document.
1.3 The infrared thermometers covered in this test method are instruments that are intended to measure temperatures below
1000°C, measure thermal radiation over a wide bandwidth in the infrared region, and are direct-reading in temperature.
1.4 This guide covers best practice in calibrating infrared thermometers. It addresses concerns that will help the user perform
more accurate calibrations. It also provides a structure for calculation of uncertainties and reporting of calibration results to include
uncertainty.
1.5 Details on the design and construction of infrared thermometers are not covered in this test method.
iTeh Standards
1.6 This test method does not cover infrared thermometry above 1000°C. It does not address the use of narrowband infrared
thermometers or infrared thermometers that do not indicate temperature directly.
(https://standards.iteh.ai)
1.7 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

conversions to SI units that are providedDocument Preview

1.8 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
for information only and are not considered standard.
2. Referenced Documents
2.1 ASTM Standards:2 ASTM E2847-14
https://standards.iteh.ai/catalog/standards/sist/1db20af1-8c8f-467c-b03d-169473c3659b/astm-e2847-14
E344 Terminology Relating to Thermometry and Hydrometry
E1256 Test Methods for Radiation Thermometers (Single Waveband Type)
E2758 Guide for Selection and Use of Wideband, Low Temperature Infrared Thermometers
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 cavity bottom, n—the portion of the cavity radiation source forming the end of the cavity.

1
This practice is under the jurisdiction of ASTM Committee E20 on Temperature Measurement and is the direct responsibility of Subcommittee E20.02 on Radiation
Thermometry.
Current edition approved May 1, 2013May 1, 2014. Published July 2013May 2014. Originally approved in 2011. Last previous edition approved in 20112013 as E2847–11.
DOI: 10.1520/E2847–13–13ε1. DOI: 10.1520/E2847–14.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.

3.1.1.1 Discussion—

The cavity bottom is the primary area where an infrared thermometer being calibrated measures radiation.
3.1.2 cavity radiation source, n—a concave shaped geometry approximating a perfect blackbody of controlled temperature and
defined emissivity used for calibration of radiation thermometers.

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States

1
 E2847 − 14
3.1.2.1 Discussion—

A cavity radiation source is a subset of thermal radiation sources.

3.1.2.2 Discussion—

To be a cavity radiation source of practical value for calibration, at least 90 % of the field-of-view of a radiation thermometer is
expected to be incident on the cavity bottom. In addition, the ratio of the length of the cavity versus the cavity diameter is expected
to be greater than or equal to 5:1.
3.1.3 cavity walls, n—the inside surfaces of the concave shape forming a cavity radiation source.
3.1.4 customer, n—the individual or institution to whom the calibration or accuracy verification is being provided.
3.1.5 distance-to-size ratio (D:S), n—see field-of-view.
3.1.6 effective emissivity, n—the ratio of the amount of energy over a given spectral band exiting a thermal radiation source to
that predicted by Planck’s Law at a given temperature.
3.1.7 field-of-view, n—a usually circular, flat surface of a measured object from which the radiation thermometer receives
radiation. (1)3

3
The boldface numbers in parentheses refer to a list of references at the end of this standard.

3.1.7.1 Discussion—

Many handheld infrared thermometers manufacturers include distance-to-size ratio (D:S) in their specifications. Distance-to-size

iTeh Standards
ratio relates to the following physical situation: at a given distance (D), the infrared thermometer measures a size (S) or diameter,
and a certain percentage of the thermal radiation received by the infrared thermometer is within this size. Field-of-view is a
measure of the property described by distance-to-size ratio. (1)
(https://standards.iteh.ai)
3.1.8 flatplate radiation source, n—a planar surface of controlled temperature and defined emissivity used for calibrations of
radiation thermometers.

3.1.8.1 Discussion—
Document Preview
ASTM
A flatplate radiation source is a subset of thermal radiation E2847-14
sources.
https://standards.iteh.ai/catalog/standards/sist/1db20af1-8c8f-467c-b03d-169473c3659b/astm-e2847-14
3.1.9 measuring temperature range, n—temperature range for which the radiation thermometer is designed. (1)
3.1.10 purge, n—a process that uses a dry gas to remove the possibility of vapor on a measuring surface.
3.1.11 radiance temperature, n—temperature of an ideal (or perfect) blackbody radiator having the same radiance over a given
spectral band as that of the surface being measured. (2)
3.1.12 thermal radiation source, n—a geometrically shaped object of controlled temperature and defined emissivity used for
calibration of radiation thermometers.
3.1.13 usage temperature range, n—temperature range for which a radiation thermometer is designed to be utilized by the end
user.
4. Summary of Practice
4.1 The practice consists of comparing the readout temperature of an infrared thermometer to the radiance temperature of a
radiation source. The radiance temperature shall correspond to the spectral range of the infrared thermometer under test.
4.2 The radiation source may be of two types. Ideally, the source will be a cavity source having an emissivity close to unity
(1.00). However, because the field-of-view of some infrared thermometers is larger than typical blackbody cavity apertures, a
large-area flatplate source may be used for these calibrations. In either case, the traceable measurement of the radiance temperature
of the source shall be known, along with calculated uncertainties.
4.3 The radiance temperature of the source shall be traceable to a national metrology institute such as the National Institute of
Standards and Technology (NIST) in Gaithersburg, Maryland or the National Research Council (NRC) in Ottawa, Ontario, Canada.
5. Significance and Use
5.1 This guide provides guidelines and basic test methods for the accuracy verification of infrared thermometers. It includes test
set-up and calculation of uncertainties. It is intended to provide the user with a consistent method, while remaining flexible in the
choice of calibration equipment. It is understood that the uncertainty obtained depends in large part upon the apparatus and

2
 E2847 − 14
instrumentation used. Therefore, since this guide is not prescriptive in approach, it provides detailed instruction in uncertainty
evaluation to accommodate the variety of apparatus and instrumentation that may be employed.
5.2 This guide is intended primarily for calibrating handheld infrared thermometers. However, the techniques described in this
guide may also be appropriate for calibrating other classes of radiation thermometers. It may also be of help to those calibrating
thermal imagers.
5.3 This guide specifies the necessary elements of the report of calibration for an infrared thermometer. The required elements
are intended as a communication tool to help the end user of these instruments make accurate measurements. The elements also
provide enough information, so that the results of the calibration can be reproduced in a separate laboratory.

6. Sources of Uncertainty
6.1 Uncertainties are present in all calibrations. Uncertainties are underestimated when their effects are underestimated or
omitted. The predominant sources of uncertainty are described in Section 10 and are listed in Table 1 and Table X1.1 of Appendix
X1.
6.2 Typically, the most prevalent sources of uncertainties in this method of calibration are: (1) emissivity estimation of the
calibration source, (2) size-of-source of the infrared thermometer, (3) temperature gradients on the radiation source, (4) improper
alignment of the infrared thermometer with respect to the radiation source, (5) calibration temperature of the radiation source, (6)
ambient temperature and (7) reflected temperature. The order of prevalence of these uncertainties may vary, depending on use of
proper procedure and the type of thermal radiation source used. Depending on the temperature of the radiation source, the
calibration method of the radiation source, the optical characteristics of the infrared thermometer and the detector and filter
characteristics of the infrared thermometer, the contribution of these uncertainties may change significantly in the overall
uncertainty budget.

7. Apparatus
7.1 Thermal Radiation Source:
iTeh Standards
7.1.1 There are two different classes of thermal radiation sources which can be used for infrared thermometer calibrations: a

(https://standards.iteh.ai)
cavity source and a flatplate source. Some sources may be considered a hybrid of both categories. Each of these sources has
advantages and disadvantages. The cavity source provides a source of radiation that has a more predictable emissivity. However,
the flatplate source can usually be made less expensively, and can be made with a diameter large enough to calibrate infrared
Document Preview
thermometers with low distance to size ratios (D:S).
7.1.2 Ideally, the size of the thermal radiation source should be specified by the infrared thermometer manufacturer. In many
cases, this information may not be available. In these cases a field-of-view test should be completed as discussed in E1256. The
portion of signal incident on the infrared thermometer ASTM E2847-14
that does not come from the source should be accounted for in the
uncertainty budget.
https://standards.iteh.ai/catalog/standards/sist/1db20af1-8c8f-467c-b03d-169473c3659b/astm-e2847-14
7.1.3 Cavity Source:
7.1.3.1 A cavity source can be constructed in several shapes as shown in Fig. 1. In general, a high length-to-diameter ratio (L:D)
or radius-to-diameter ratio (R:D) in the spherical case will result in a smaller uncertainty. A smaller conical angle Φ will also result
in a smaller uncertainty.
7.1.3.2 The location of a reference or a control probe, or both, and the thermal conductivity of the cavity walls are important
considerations in cavity source construction. In general, a reference or control probe should be as close as practical to the center
of the area where the infrared thermometer will typically measure, typically the cavity bottom. If there is a separation between the
location of the reference probe and the cavity surface, cavity walls with a higher thermal conductivity will result in a smaller
uncertainty due to temperature gradients in this region.

TABLE 1 Components of Uncertainty

Uncertainty Component Discussion Evaluation Method
Source Uncertainties
U1 Calibration Temperature 10.4 10.4.1
U2 Source Emissivity 10.5 10.2.3, X2.4 (example)
U3 Reflected Ambient Radiation 10.6 10.2.2, X2.5 (example)
U4 Source Heat Exchange 10.7 10.7.1
U5 Ambient Conditions 10.8 10.8.1
U6 Source Uniformity 10.9 10.9.1
Infrared Thermometer Uncertainties
U7 Size-of-Source Effect 10.11 Test Methods E1256
U8 Ambient Temperature 10.12 Appendix X3
U9 Atmospheric Absorption 10.13 X2.3
U10 Noise 10.14 10.14.1
U11 Display Resolution 10.15 10.15.2

3
 E2847 − 14

iTeh Standards
(https://standards.iteh.ai)
Document Preview FIG. 1 Cavity Shapes

7.1.3.3 The walls of the cavity source can be treated in several different ways. A painted or ceramic surface will generally result
in higher emissivity than an oxidized metal surface. ByASTMthe sameE2847-14
measure an oxidized metal surface will generally result in higher
https://standards.iteh.ai/catalog/standards/sist/1db20af1-8c8f-467c-b03d-169473c3659b/astm-e2847-14
emissivity than a non-oxidized metal surface. In some cases, it may be impossible to paint the cavity source surface. This is
especially true at high temperatures.
7.1.3.4 The effective emissivity of the cavity source shall be calculated to determine the radiance temperature of the cavity.
Calculation of effective emissivity is beyond the scope of this standard. Determination of effective emissivity can be
mathematically calculated or modeled.
7.1.4 Flatplate Source:
7.1.4.1 A flatplate source is a device that consists of a painted circular or rectangular plate. The emissivity is likely to be less
well defined than with a cavity source. This can be partially overcome by performing a radiometric transfer (see Scheme II in 7.3.7)
to the flatplate source. However, the radiometric transfer should be carried out with an instrument operating over a similar spectral
band as the infrared thermometer under test.
7.1.4.2 A cavity source is the preferred radiometric source for infrared thermometer calibrations. The cavity source has two
main advantages over a flatplate source. First, the cavity source has better defined emissivity and an emissivity much closer to unity
due to its geometric shape. Second, along with the emissvity being closer to unity, the effects of reflected temperature are lessened.
Temperature uniformity on the flatplate source may be more of a concern as well. However, a flatplate source has a main advantage
over a cavity source. The temperature controlled flatplate surface can be much larger than a typical cavity source opening, allowing
for much smaller D:S ratios (greater field-of-view).
7.2 Aperture:
7.2.1 An additional aperture may not be needed for all calibrations. An aperture is typically used to control scatter. If used, the
aperture should be temperature-controlled or reflective. An aperture should be used if recommended by the infrared thermometer
manufacturer. If an aperture is used for calibration, this information should be stated in the report of calibration. The information
that shall be included is the aperture distance, the aperture size, and the measuring distance. A possible configuration for aperture
use is shown in Fig. 2.
7.2.2 In Fig. 2, dapr is the aperture distance. The measuring distance is shown by dmeas.
7.3 Transfer Standard:

4
 E2847 − 14

FIG. 2 Use of an Aperture for a Calibration

iTeh Standards
7.3.1 The thermal radiation source shall be calibrated with a transfer standard traceable to a national metrological institute such
as the National Institute of Standards and Technology (NIST) or National Research Council (NRC). If a reference thermometer

(https://standards.iteh.ai)
(radiometric or contact) is used during the calibration of the unit-under-test, this serves as the calibration of the radiation source.
In this case, the reference thermometer shall have a calibration traceable to a national metrological institute.
7.3.2 This calibration of the thermal radiation source may take place in the calibration laboratory, or it may be done by a third
Document Preview
party calibration laboratory. The interval of these checks is determined by the calibration laboratory. The drift related to the
calibration interval is part of the calibration uncertainties for the infrared thermometer calibration.
7.3.3 Regardless of whether a cavity source or a flatplate source is used, there are two approaches to calibrating the source:
contact calibration (Fig. 3, Scheme I) and radiometricASTM E2847-14
calibration (Fig. 3, Scheme II). (3)
7.3.4 In Fig. 3 the arrows show the path of traceability to the International System of Units (SI) through a national metrological
https://standards.iteh.ai/catalog/standards/sist/1db20af1-8c8f-467c-b03d-169473c3659b/astm-e2847-14
institute (NMI). The reference radiation source is the cavity source or blackbody source used to calibrate the infrared thermometer.
In Scheme I, it is shown that the ∆T measurement and the emissivity correction shall be added into the temperature calculation.

FIG. 3 Calibration Schemes I and II

5
 E2847 − 14
The ∆T measurement is based on the difference in temperature between the reference thermometer and the cavity walls. The
emissivity correction is based on the radiation source not having the same emissivity as the infrared thermometer’s emissivity
setting. The symbol λ1 refers to the wavelength and bandwidth of the transfer radiation thermometer and the infrared thermometer.
7.3.5 In either scheme, the transfer standard shall be traceable to a national metrological institute.
7.3.6 In Scheme I, a contact thermometer is used as the transfer standard. The emissivity uncertainties become of greater
concern. This is especially the case when using a flatplate source.
7.3.7 In Scheme II, a radiation thermometer is used as the transfer standard. In this scheme, the emissivity and heat exchange
uncertainties are greatly reduced. This is especially significant in the case of using a flatplate source. the radiation thermometer
should operate over a similar spectral range as the infrared thermometer to be calibrated. Any differences in spectral range will
result in additional uncertaintes. For instance, if the radiation source is calibrated with an 8 to 14 µm radiation thermometer, and
an infrared thermometer with a 7 to 14 µm spectral response is being calibrated, even this difference in bandwidth shall be
accounted for in the uncertainty budget, since the radiance temperature (due mostly to the effective emissivity) will be different.
7.4 Ambient Temperature Thermometer:
7.4.1 The ambient temperature should be monitored during the calibration to ensure that it is within the laboratory’s limits. This
should be done using a calibrated thermometer. At a minimum, the laboratory’s ambient temperature limits should be recorded on
the report of calibration.
7.5 Mounting Device:
7.5.1 The infrared thermometer may be mounted on a tripod or similar mounting fixture. Mounting may not be required in the
case of a manually held calibration. In this case the hand is the mounting device.
7.6 Distance Measuring Device:
7.6.1 The distance between the radiation source and the infrared thermometer is a critical factor in calibration. This distance
should be either measured during the infrared thermometer calibration or set by fixturing. This measuring distance along with the
target size shall be recorded on the report of calibration.

iTeh Standards
7.7 Calibrations Below the Dew-Point or Frost-Point:
7.7.1 For calibrations where the set-point of the radiation source is below the dew or frost point, it may be necessary to purge

(https://standards.iteh.ai)
the area around the source with a dry gas such as dried nitrogen or dried air to prevent ice buildup. It may be desirable to use a
vacuum for this purpose. It is beyond the scope of this standard to recommend a specific design or method for such a purge.

8. Preparation of Apparatus
8.1 Infrared Thermometer:
Document Preview
8.1.1 The infrared thermometer should be allowed to reach ambient temperature before any measurements are made. The
amount of time may be specified by the manufacturer.ASTM If this isE2847-14
not the case, experimentation may need to be done to determine
https://standards.iteh.ai/catalog/standards/sist/1db20af1-8c8f-467c-b03d-169473c3659b/astm-e2847-14
the proper time for the device to thermally stabilize. This uncertainty should be accounted for in the ambient temperature section
of the uncertainty budget.
8.1.2 If a lens cleaning is required, it shall be performed following the manufacturer’s guidelines.
8.2 Radiation Source:
8.2.1 The radiation source should be set to the desired calibration temperature and allowed to stabilize at the set calibration
temperature. Any effects due to settling time should be accounted for in the uncertainty budget.
8.2.2 If a purge device is used with the radiation source for the calibration, it should be in place before the radiation source is
stabilized.

9. Procedure
9.1 Calibration Points:
9.1.1 The number of calibration points used during a calibration should be determined by the customer. If the customer does
not know what points to use for a calibration, a recommendation may be made. For an infrared thermometer used over a narrow
range of temperature, one point may be enough. For an infrared thermometer used over a wide range of temperature, a minimum
of three calibration points should be chosen. These points should represent at least the minimum, maximum and midpoint
temperature of the infrared thermometer usage temperature range. The usage range may not be the same as the measuring
temperature range of the infrared thermometer.
9.1.2 The order of calibration points may be arbitrary. However, it is important to note that heating of the infrared thermometer
by the calibration source may cause a condition similar to thermal shock. This is especially true when going from a calibration
source at a higher temperature to a calibration source at a lower temperature. Thus, it is best practice to calibrate at lower
temperature points before higher temperature points.
9.2 Steps 9.3 to 9.6 should be repeated for each calibration point.
9.3 Reflected Temperature: