Department of Mechanical Engineering 1
INSTRUMENTATION &
CONTROL
SYSTEMS(I&CS)
UNIT 1
MEASUREMENT & INSTRUMENTATION
SASHANK ASSISTANT PROFESSOR, GRIET
INTRODUCTION
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Instrumentation is a part of engineering science that involves
continuous monitoring and controlling of physical parameters to
increase the safety in working areas
It deals with various methods used for measurement, measuring
instruments employed and the problems associated with the
methods used for measurement
It plays a major role in both measuring and collecting information
from working areas and changing the field parameters as
required for the process
Control System is defined as a means by which a set of variable
quantities is held constant or caused to vary in a prescribed way
Department of Mechanical Engineering
OBJECTIVES
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To measure and control the field parameters to
increase safety and efficiency of the process
To maintain the operation of the plant within the
design expectations and to achieve a good quality
product
To achieve automatic control of process
To perform manipulation on the collected data
automatically
To achieve, good quality control
Department of Mechanical Engineering
CALIBRATION
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Calibration is a process of making a set of operations
to establish a relationship between the values indicated
by the measuring system and the corresponding known
value of the physical quantity
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CALIBRATION
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Static error is the numerical algebraic difference
between the value obtained by the measurement of the
quantity and the true value of the same quantity
Relative error(Fractional error) is defined as the ratio
of the static error to the true quantity
Department of Mechanical Engineering
MEASUREMENT & INSTRUMENT
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Measurement provides us with means for describing
the various physical and chemical parameters of
materials in quantitative terms
Instrument is the one which provide accurate
measurement in the technology fields
Instrument would sense a physical parameter and
translates into a format that can be interpreted
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MEASUREMENT METHODS
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Measurement Methods
Direct and Indirect Measurements
Primary, Secondary and Tertiary Measurements
Contact and Non-Contact type Measurements
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CLASSIFICATION OF MEASURING INSTRUMENTS
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Manual and Automatic Instruments
Self Generating and Power Operated Instruments
Self Contained and Remote Indicating Instruments
Deflection and Null Output Instruments
Analog and Digital Instruments
Contacting and Non-Contacting Instruments
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TYPES OF ERRORS
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Gross Errors
Systematic Errors
InstrumentalErrors
Environmental Errors
Observational Errors
Random or Accidental Errors
Certain Human Errors
Errors caused due to the disturbance to the equipment
Errors caused by fluctuating experimental conditions
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SOURCES OF ERRORS
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Calibration of Instrument
Instrument Reproducibility
Measuring Arrangement
Environmental Conditions
Work Piece
Observer’s Skill
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PERFORMANCE CHARACTERISTICS
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The Performance Characteristics of an instrumentation
system is concluded by how accurately the system
measures the required input and how absolutely it
rejects the undesirable inputs
Static
Characteristics
Dynamic Characteristics
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STATIC PERFORMANCE CHARACTERISTICS
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The Characteristics that does not vary with time are known as
static characteristics. These are determined by static calibration in
which the relationship between the output signal and the quantity
under study is experimentally determined
Accuracy, Precision, Sensitivity
Linearity
Stability
Error
Threshold
Resolution
Hysteresis
Dead space
Range and span
Reproducibility
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ACCURACY, PRECISION & SENSITIVITY
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Accuracy is the degree of closeness with which the
output of the instrument reached the true value of
the quantity being measured
Precision is the ability of the measuring system to
reproduce the same output values among several
independent measurements under specified
conditions within a given accuracy
Sensitivity is the ratio of magnitude of the output to
the magnitude of the input quantity being measured
Department of Mechanical Engineering
LINEARITY, STABILITY & ERROR
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Linearity is expressed as a percentage of deviation
from the linear value
Stability is the ability of the instrument to have the
same standard of performance over a prolonged
period of time
Error is the difference between the measured value
and the true value
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THRESHOLD, RESOLUTION, HYSTERESIS
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The smallest increment of quantity being measured
which can be detected with certainty by an
instrument represents the Threshold and Resolution
of the instrument
The dependence of output upon previous inputs is
called as Hysteresis
The change of input quantity upto the maximum
extent for which there is no output of instrument is
known as Dead Space
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DYNAMIC PERFORMANCE CHARACTERISTICS
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The Characteristics that varies with time are known as
dynamic characteristics. They are determined from the
mathematical model of a system
Bandwidth
Dynamic Range
Measurement Lag
Fidelity
Speed of Response
Dynamic Error
Settling Time
Time Constant
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DYNAMIC PERFORMANCE CHARACTERISTICS
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The dynamic sensitivity is obtained for certain range of
frequencies and this range of frequencies are known as
bandwidth
Dynamic Range is the range of signals for which the measuring
system is possible to respond constantly under dynamic
conditions
Measurement Lag is the time delay in response of the output
signal to the changes in the measured quantity
Fidelity is the degree of nearness with which the output
reproduces the time varying input within a conversion factor
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DYNAMIC PERFORMANCE CHARACTERISTICS
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Speed of Response is the quickness of an instrument with which it
responds to the sudden changes in amplitude of the input signal
Dynamic Error is the difference between the value indicated by
the measuring system and the true value of the quantity
Settling Time is the time required by the response of the system to
reach and stay within the close range of the steady state output
value
Time Constant is the time required for the output of the system to
reach 63.2% of the final output value
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GENERALIZED MEASURING SYSTEM
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Measurement is the conversion of physical
parameters into their corresponding numerical
values
The object’s property will be compared to a
standard unit i.e a unit which is already defined for
the particular property
The objective of measuring instrument is to provide
a numerical value which is proportional to the
quantity of the variable being measured
Department of Mechanical Engineering
GENERALIZED MEASURING SYSTEM
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Functional Elements
The instrumentation system contains following elements
Primary Sensing Elements (Any Sensor)
Variable Conversion Elements (Transducer)
Variables Manipulation Element(Electrical Amplifier)
Data Transmission Element (Cables, Radio Signals)
Data Processing Element(Convert Data into Useful Form)
Data Storage and Presentation Element (Digital display,
storage devices & Movement of pointer over calibrated
scale)
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GENERALIZED MEASURING SYSTEM
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GROUPINGS OF GENERALIZED MEASURING SYSTEM
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Functional Elements into 3 Groups
Input Stage (Detector-Transducer)
Variable to be Measured, Transforming the Signal
Intermediate Stage (Signal Conditioning)
Signal Amplification, Signal Filtration, Signal
Modification, Data Transmission
Output Stage (Data Presentation)
Visual Display, Graphic Record, Audible Alarms,
Numerical Readout
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INPUT-OUTPUT CONFIGURATION OF
MEASURING INSTRUMENTS
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The input-output relationship is characterised by the
operational transfer function ‘G’
The various inputs to the measurement system are
Desired Input(iD)
Interfering
Input(iI)
Modifying Input(iM)
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IDENTIFY THE FUNCTIONAL ELEMENTS IN
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DIAL INDICATOR
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IDENTIFY THE FUNCTIONAL ELEMENTS IN
PRESSURE ACTUATED THERMOMETER
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IDENTIFY THE FUNCTIONAL ELEMENTS IN
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DIGITAL REVOLUTION COUNTER
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IDENTIFY THE FUNCTIONAL ELEMENTS IN
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PRESSURE LEVEL SENSOR
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IDENTIFY THE FUNCTIONAL ELEMENTS IN
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LIQUID LEVEL FLOAT
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