Electronic Measurement and Instrumentation

Course Name: Electronic Measurement
and Instrumentation
Course Code: MC1307
Course Instructor- Princy Randhawa
Wednesday, February 6, 2019 1

Wednesday, February 6,
2019
2
Course Outcomes
CO.1 [MC1307.1] Measure various electrical parameters with accuracy, precision,
resolution.
CO.2 [MC1307.2] Explain the use of various electrical/electronic instruments, their
construction, principles of operation, standards and units of
measurements.
CO.3 [MC1307.3] Explain the industrial and laboratory applications of Electrical/Electronic
instruments.
CO.4 [MC1307.5] Understand the concept of AC and DC bridges for the measurement of
Resistance, Inductance and Capacitance.
CO.5 [MC1307.4] Select appropriate passive or active transducers for measurement of
physical phenomenon like temperature, pressure, flow, liquid level,
displacement, speed etc.

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Course Syllabus
Basic concepts of measurements: System configuration, calibration - Errors in measurements,
measuring instruments: Permanent magnet moving coil, Moving iron, Electrodynamometer type
and Rectifier type instruments, Applications - Measurement of Resistance, Inductance &
Capacitance: A.C. Bridges. Temperature Measurement: Temperature and heat, Definitions,
temperature scales, bimetallic thermometers, filled-bulb and glass stem thermometers, Resistance
Temperature Detector (RTD), principle and types, measuring circuits, Linear and Quadratic
approximation Thermistors, Thermocouples, optical pyrometers, Pressure Measurement:
Manometers, Elastic types, Bell gauges, Electrical types, Differential Pressure transmitters, Dead
weight Pressure gauges, Low Pressure Measurement: Mc. Leod gauge, Knudsen gauge, Pirani
gauge, Thermal conductivity gauges, Ionization gauge. Flow measurement: Classification of flow
meters, orifice meters, Venturi Flow meter, variable area flow meters, Laser Doppler
Anemometer (LDA), ultrasonic flow meters, Doppler flow meters, V-cone flow meters, purge
flow regulators, Measurement of mass flow rate: Radiation, angular momentum, Displacement
measurement (LDR, Photodiode, LVDT), Vibration measurement, Level Measurement, Angular
Velocity Measurement

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Course Objective
To provide students with a fundamental understanding
of the concepts, principles, procedures and the
computations used by engineers and technologies to
analyse select, specify design and maintain modern
instrumentation.

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Course Summary
This course is electronics based course dealing with measurements and
instrumentation designed for students in Physics Electronics, Electrical
and Electronics Engineering and allied disciplines. It is a theory course
based on the use of electrical and electronics instruments for
measurements. The course deals with topics such as Principle of
measurements, Errors, Accuracy, Units of measurements and electrical
standards, , introduction to the design of electronic equipment’s for
temperature, pressure, level, flow measurement, speed etc.

2019
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Books/References
Text Books:
• A.K. Sawhney, Electrical & Electronic Measurements and
Instrumentation, Dhanpat Rai & Co, New Delhi, 19th Edition, 2011.
• E. O. Doeblin, Measurement Systems: Application and Design,
McGraw Hill, New York, 6th Edition, 2012.
References:
• D. Patranabis, Principles of Industrial Instrumentation, Tata McGraw
Hill, New Delhi, 3rd Edition, 2010.
• A. K. Sawhney, A course in Mechanical Measurement and
Instrumentation, Dhanpat Rai and Co, New Delhi, 12th edition, 2002.
• Bela G. Liptak, Process Measurement and Analysis, Chilton Book
Company, Pennsylvania, 4th Edition, 2012

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Marks Scheme
 30 Marks –Sessional I & 2
 30 Marks Assignment
- Tutorial -5 Marks
- Quiz -10 marks
- Seminar -10 Marks
- Class Performance and Attendance- 5 marks
90 above- 5 marks
85-89- 4 marks
80– 84-3 marks
75-79 -2 marks
< 75 – 0 marks
 40 Marks –End Semester

Electrical & Electronics
 Electronics is a subset of electrical where you influence and control the behaviour
of electrons in a circuit by another current, without mechanical parts (switches,
relays ) or electro magnetism (coils, oscillators)
 Electric things are those deal with higher voltages , transformers , generators etc.
where as electronic are those which uses low voltages like IC.s of mag (0-15 V)
Electronics
X1
X2
X3
Y1
Y2
Y3
Inputs Outputs

Introduction
Instrumentation : Instrumentation is the use
of measuring instruments to monitor and
control a process. It is the art and science of
measurement and control of process variables
within a production, laboratory, or
manufacturing area.
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Few Definitions
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Measurement: It is the act, or the result of quantitative comparison between a
predetermined std. and or an unknown magnitude. Since two quantities are compared and
the result are expressed in numerical value.
Measurand: The physical quantity or the characteristic conditions which is the object of
measurement in an instrumentation system is termed as measurand or measurement
variable or process variable.
e.g. Fundamental Quantity: length, mass, time et.
Derived Quantity : Speed, Velocity, Pressure etc.
Process of Comparison
Std. Unknown Quantity
Measurand (Qty. to be measured)
Result (Read out)

Significance of Measurement
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“When you can measure, what you are speaking and express it
in numbers, you know something about and can express it in
numbers, you know something about it, when you cannot
express in it numbers in knowledge is of meagre and
unsatisfactory kind” – Lord Kelvin
The measurement confirms the validity of a hypothesis and
also add to it the understanding. This eventually leads to new
discoveries that require new and sophisticated measuring
techniques.
Through measurement a product can be designed or a process
be operated with max. efficiency , minimum cost and with
desired degree of reliability and maintainability

Contd..
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Measured Value: Any value or any reading calculated from measurement system
or measuring instrument.
True value: Any value calculated from rated value known as True value of Actual
Value.
e.g. Motor Actual Speed
Error : Any deviation of measured
value from true value
Measured Value-True Value
Measuring Instrument
True Value Measured Value

Methods of Measurement
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Direct Method Indirect Method
The unknown quantity (measurand) In this method the comparison
is directly compared against a standard. Is done with a standard through
The result is expressed as a numerical number the use of a calibration s/m. These
and a unit. Direct methods are common methods are used those cases
for the measurement of physical quantities where the desire parameter to
like length, mass and time be measured. E.g. Acceleration,
power
Method of Measurement

Direct Methods Classified as:
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Deflection methods
Deflection method” includes the deflection of pointer on a scale due
to the quantity to be measured. Example: Wattmeter, ammeter
voltmeter
Comparison methods
“Comparison method” include the comparison of the quantity under
measurement with a pre-defined standard quantity which gives
measurement. Example: potentiometer

Sensor VS transducer
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Functional Elements of an Instruments
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Any instrument or measuring can be represented by block
diagram, that indicates necessary elements and its functions.
The entire operation of the measuring system can be
understand fro the bock diagram
Primary
sensing
element
Variable
conversion
element
Variable
manipulation
element
Data
transmission
element
Data
presentation
element
Qty. to be
measured
Data conditioning element Observer
Data storage element

Take an example:
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 Just take an example of an Analog meter (Ammeter) which
measures current.
Moving
Coil
Magnets and other
components
Mechanical
Linkages
Pointers and
scale
Current
Data conditioning ObserverPrimary Sensing Data Transmission
Force
BASIC SCHEMATIC OF AN AMMETER

Classification of Instruments
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Measurement involve the use of instruments as a physical means of
determining quantities or variables.
 Absolute/ Secondary Instruments
 Analog/ Digital Instruments
 Mechanical/Electrical or Electronic Instruments
 Active/Passive Instruments
 Manual/Automatic Instruments
 Self contained /Remote Indicating Instruments
 Deflection/null o/p instruments

Active/Passive Instruments
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Absolute or Primary/Secondary
Instruments
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Absolute Instruments
 It gives the magnitude of quantity under measurement in
terms of physical constants of the instrument e.g. Tangent
Galvanometer
 In this type of instruments no calibration
or comparison with other instruments is necessary.
 They are generally not used in laboratories and
are seldom used in practice by electricians and engineers.
Secondary Instruments
 These instruments are so constructed that the quantity being measured can only be
determined by the output indicated by the instrument.
 These instruments are calibrated by comparison with an absolute instrument or another
secondary instrument, which has already been calibrated against an absolute instrument.
e.g. Ammeter, Voltmeter etc.

Classification of Secondary
Instruments
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(a) Classification based on the various effects of electric current (or voltage) upon which
their operation depend.
• Magnetic effect: Used in ammeters, voltmeters,
watt-meters, integrating meters etc.
• Heating/thermal effect: Used in ammeters and voltmeters.
• Electromagnetic field of attraction/repulsion
• Electrostatic effect: Used in voltmeters.
• Electromagnetic induction effect: Used in ac ammeters,
voltmeters, watt meters and integrating meters.
(b) Classification based on the Nature of their Operations
• Indicating instruments: Indicating instruments indicate, generally the quantity to be
measured by means of a pointer which moves on a scale. Examples are ammeter, voltmeter,
wattmeter etc.
• Recording instruments: These instruments record continuously the variation of any
electrical quantity with respect to time. In principle, these are indicating instruments but so
arranged that a permanent continuous record of the indication is made on a chart or dial

Classification of Secondary
Instruments
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Integrating instruments: These instruments record the consumption of the total quantity of
electricity, energy etc., during a particular period of time. : Ampere-hour meter: kilowatt thour
(kWh) meter, kilovolt-ampere-hour (kVARh) meter.
(c) Classification based on the Kind of Current that can be Measurand.
• Direct current (dc) instruments
• Alternating current (ac) instruments
(d) Classification based on the method used
Direct measuring instruments: These instruments converts the energy of the measured
quantity directly into energy that actuates the instrument and the value of the unknown
quantity is measured or displayed or recorded directly Examples are Ammeter, Voltmeter,
Watt meter etc.
• Comparison instruments: These instruments measure the unknown quantity by comparison
with a standard. Examples are dc and ac bridges and potentiometers. They are used when a
higher accuracy of measurements is desired

Analog /Digital Instruments
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Analogue Instruments: The signal of an analog unit vary in a
continuous fashion and can take an infinite no. of values in a given
range. E.g. ammeters, voltmeter, wrist watch , speedometer etc.
Digital instruments: Signals varying in discrete steps and taking on
a finite no. of different values in a given range are digital signals e.gs
timer on a score board, odometer of an automobile

Analog Instruments
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Analog Instruments
Quantity to be measured
 Current-Ammeter
 Voltage-Voltmeter
 Power-Wattmeter
P=V x I
 Energy –Energy Meter
E=
0
𝑡
𝑃𝑑𝑡
Working Principle
Representation
Indicating type Recording type Integrating type Null Deflection
 Magnetic field effect
 Electrostatic field effect
 Electromagnetic Field of
attraction/repulsion
 Induction effect
 Heating effect

Deflection /Null o/p Instruments
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Deflection Null
 Only one source of input reqd. Require two input- measurand
and balance input
 Output reading is based on the deflection Must have feedback operation that
from the initial condition of the instrument compares the measurand with std. value
• The measurand value of the qty. depends Most accurate and sensitive
on the calibration of the instrument

Essential Requirements of Indicating
Instruments
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1. Deflecting torque (Td) : Deflecting torque causes the moving system and
pointer of the instrument to move from its zero position. Production of
deflecting torque depends upon the type of indicating instrument and its
principle of operation
2. Controlling torque (Tc) : Controlling torque limits the movement of pointer
and ensures that the magnitude of deflection is unique and is always same for
the given value of electrical quantity to be measured.
Two methods of Controlling Torque
i. Spring Control method
ii. Gravity control method

Spring Control Method
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 Two phosphor bronze hair springs of spiral
shapes are attached to the spindle of the
moving system of the instrument.
 They are wound in opposite direction
 Pointer is attached to the spindle of the
moving system

Gravity Control Method
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 In gravity control method, a
small weight is attached to the
spindle of the moving system
 Due to the gravitational pull, a
control torque (acting in
opposite direction to the
deflecting torque) is produced
whenever the pointer tends to
move away from its initial
position.

Instruments
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Instruments
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3. Damping Torque: Damping torque minimizes the oscillations of the pointer about the final
steady state deflection and makes it steady.. In the absence of this torque, pointer continues
oscillating to its final position after reaching to its final position. Depending on the
magnitude of damping, it can be classified as underdamped, over damped and critically
damped

Damping Methods
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Air friction Damping
Fluid Friction Damping
Electromagnetic/ Eddy current
Damping

Air Friction Damping
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Fluid Friction Damping
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Eddy Current Damping
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Types of Instruments
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1. Permanent Magnet Moving Coil (PMMC) type
Instrument.
2. Moving Iron type Instrument
3. Electro Dynamometer type Instrument
4. Hot wire type Instrument
5. Thermocouple type Instrument
6. Induction type Instrument
7. Electrostatic type Instrument
8. Rectifier type Instrument

Permanent Magnet Coil Instrument
(PMMC)
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(PMMC)- Torque Equation
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38
Controlling Torque: The value of
control torque depends on the mechanical
design of the control device. For spiral
springs and strip suspensions, the
controlling torque is directly proportional
to the angle of deflection of the coil.

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39
It is provided by the induced currents in a metal former or core on which the coil is wound or
in the circuit of the coil itself.

Errors
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Frictional Error
Temperature Error
Errors due weakening of permanent magnet
Error due to ageing of spring
Stray magnetic field error

Advantages of PMMC
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Low Power consumption
Scales are uniform
No hysteresis loss (iron loss)
High Torque/wt. ratio
They have a very effective and efficient eddy current
damping
Range can be extended with shunts or multipliers

disadvantages of PMMC
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Use only for dc
 The cost of these instruments is higher than that of
moving iron instrument

Numericals
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1. A permanent magnet moving coil instrument has a coil of dimensions 15mm x 12 mm.
The flux density in the air gap is 1.8 x 103 Wb/𝑚2 and the spring constant is 0.14 x 10−6
Nm/rad. Determine the number of turns required to produce an angular deflection of 90
degrees when a current of 5mA is flowing through the coil.
2. The control spring of an instrument has the following dimensions:
Length of strip =370 mm , thickness of strip =0.073 mm, width of strip= 0.51mm
The young modulus is 112.8 GN/𝑚2. Estimate the torque exerted by spring when it is
turned through 90 𝑜
.
3. The coil of a moving coil voltmeter is 40mm long and 30mm wide and has 100 turns on
it. The control spring exerts a torque of 240 x 10−6
N-m when the deflection is 100
divisions on full scale. If the flux density of the magnetic field in the air gap is 1.0
wb/𝑚2, estimate the resistance that must be put in series with the coil to give one volt per
division. The resistance of the voltmeter coil may be neglected.

Ammeter Shunts
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DC Ammeter
Its is always connected in series
low internal resistance
maximum pointer deflection is produced by a very small current
For a large currents, the instrument must be modified by connecting a
very low shunt resister
 Extension of Ranges of Ammeter
- Single Shunt Type of Ammeter

Ammeter Shunts
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m
mm
sh
msh
sh
mm
sh
mmshsh
msh
II
RI
R
III
I
RI
R
RIRI
VV







Ammeter Shunts
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Multirange Ammeters
Make-before-break switch
The instrument is not left without a shunt in
parallel with it.
During switching there are actually two shunts
in parallel with the instrument.

Ayrton or Universal Shunts
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Numerical
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Design an Aryton shunt to provide an ammeter with a current ranges 1A, 5A and 10A. A
basic meter resistance is 50 ohms and full scale deflection current is 10mA.

Numerical
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Voltmeter Multipliers
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A basic d’Arsonval movement can be converted into dc voltmeter by adding in series
resistor multiplier as shown in figure.

Multirange dc Voltmeter
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A DC voltmeter can be converted into a multirange voltmeter by connecting a number
of resistors (multipliers) in series with the meter movement. A practical multi-range DC
voltmeter is shown in Figure

Ammeter/Voltmeter Sensitivity
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 Ammeter sensitivity is determined by the amount of current required by the meter coil to
produce full-scale deflection of the pointer.
 The smaller the amount of current required producing this deflection, the greater the
sensitivity of the meter.
 The sensitivity of a voltmeter is given in ohms per volt. It is determined by dividing the sum
of the resistance of the meter (Rm), plus the series resistance (Rs), by the full-scale reading in
volts. In equation form, sensitivity is expressed as follows:
 This is the same as saying the sensitivity is equal to the reciprocal of the full-scale deflection
current. In equation form, this is expressed as follows:

PMMC Animation
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Numericals
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 Calculate the value of the shunt resistance required to convert a 1-mA meter movement,
with a 100 Ohm internal resistance, into a 0- to 10 mA ammeter
 Compute the value of the shunt resistors for the circuit below. I3 = 1A, I2 = 100 A, I1 = 10
mA, Im = 100 uA and Rm = 1K Ohm.

Solutions
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 Solution 1:
    VmA
RIV mmm
1.0100*1 





11.11
9
1.0
9110
1.0
mA
V
I
V
R
mAmAmA
III
VVV
sh
sh
sh
msh
msh
 Solution 2 : This is the shunt for the 10 mA
range. When the meter is set on the 100-mA
range, the resistor Rb and Rc provide the shunt
. The total shunt resistance is found by the
equation.





 1.10
1100
1
1
K
n
R
R m
sh





01.1
100
)11.10(*)100(
)(
2
mA
KuA
I
RRI
RR cbm
cb





101.0
1
)11.10(*)100(
)(
2
A
KuA
I
RRI
RR cbm
cb


909.0101.001.1
)( ccbb RRRR


909.0)101.0909.0(1.10
)( cbsha RRRR


1.10101.0909.009.9
cbash RRRR

Moving Iron Instruments
-Torque Equation
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Classification
1. Moving Iron Attraction Type Instruments
1. Moving Iron Repulsion Type Instruments.

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 Radial Vane Type
 Coaxial Vane Type

Torque Equation
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Torque Equation
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Advantages
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 Can be used both in D.C. as well as in A.C. circuits.
 Robust and simple in construction.
 Possess high operating torque.
 Can withstand overload momentarily.
 Since the stationary parts and the moving parts of the instrument are
simple so they are cheapest.
 Suitable for low frequency and high power circuits.
 Capable of giving an accuracy within limits of both precision and
industrial grades.

Limitations
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 Scales not uniform.
 For low voltage range the power consumption is higher.
 The errors are caused due to hysteresis in the iron of the operating system and due to
stray magnetic field.
 In case of A.C. measurements, change in frequency causes serious error.
 With the increase in temperature the stiffness of the spring decreases.

Errors
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1.Hysteresis error : This error occurs as the value of flux density is different of same current for
ascending and descending values. The flux density is higher for descending value there for instruments
read higher for descending value current this error can be minimize using small iron parts and other
method is used nickel iron alloy
2.Temperature error: the effect of temperature change on moving iron instruments aries chiefly from the
temperature coefficient of spring.for minimize the error the series resistance should be made of material
like Manganin which has small temperature coefficient. the value of resistance should large as compare
with coil resistance.in order to reduce the self heating.
3.Stray Magnetic fields: It is a also called demagnetization fields. this is weak at full scale deflection
hence it can easily distorted . these error can be minimized using an iron case or iron shied over working
parts
Errors with A.C. only:
1.Frequency error: Change in frequency is also cause of change in reactance of working coil and also
change the eddy currents setup in the metal parts of instrument.
2.Reactance of Instruments coil: the change of reactance of the instrument coil is importance in case of
voltmeter. where a addition resistance put in series with instrument coil to reduce this effect.
Errors with both A.C and D.C

Moving Iron Instrument Animation
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Moving Iron Instrument (Repulsive)
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Electrodynamometer Instruments
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Electrodynamometer Instruments
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Torque Equation
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Torque Equation
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Torque Equation
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Advantages
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 As the coils are air cored, these instruments are free from
hysteresis and eddy current losses.
 They have a precision grade security
 These instruments can be used on both a.c. and d.c. They are also
used as a transfer instruments.
 Electrodynamometer voltmeter are very useful where accurate
r.m.s values of voltage, irrespective of waveforms, are required.
 Free from hysteresis errors.
 Low power Consumption.
 Light in weight.

Disadvantages
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 These instruments have a low sensitivity due to a low torque to
weight ratio. Also it introduces increased frictional losses. To get
accurate results, these errors must be minimized.
 They are more expensive than other type of instruments.
 These instruments are sensitive to overload and mechanical
impacts. Therefore can must be taken while handling them.
 They have a non-uniform scale.
 The operation current of these instruments is large due to the fact
that they have weak magnetic field.

Errors
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1. Torque to weight ratio
2. Frequency errors
3. Eddy current errors currents.
4. Stray magnetic field error :.
5. Temperature error :

Numericals
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1. In an electrodynamometer instrument the total resistance of the voltage coil circuit is
8.00 Ω and mutual inductance changes uniformly from -173µH at zero deflection to +
175µH at full scale, the angle of full scale being 95 degree. If a potential difference of
100V is applied across the voltage circuit, and a current of 3A at a power factor of 0.75 is
passed through the current coil, what ill be the deflection , if the spring control constant is
4.63 x 106
𝑁 − 𝑚/𝑟𝑎𝑑

Characteristics of Instruments
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The performance of an instrument is described by means
of a quantitative qualities termed as characteristics. These
are broken down into:
1. Static Characteristics: These characteristics pertain to
a system where the quantities to be measures are
constant or vary slowly with time
2. Dynamic Characteristics: Performance criteria based
on dynamic relations (involving rapidly varying
quantities)

Static Characteristics
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 Accuracy
It is the closeness with which an instrument reading approaches the
true value of the quantity measured.
 Precision : The degree to which repeated measurements show the
same results.
Low Accuracy
Low Precision
High Accuracy
Low Precision
Low Accuracy
High Precision
High Accuracy
High Precision

Accuracy and Precision
2019
Accuracy may be specified in terms of inaccuracy or limit of errors
and can be expressed in the following ways:
1. Point Accuracy
2. Accuracy as “Percentage of Scale Range”
3. Accuracy as “Percentage of True value”
Indication of Precision
Significant Figures: It is an indication of precision of measurement. It
convey the actual information regarding the magnitude and the
measurement precision of a qty. The more the significant figures, the
greater the precision.
e.g. 302 A = 3S.F
302.10 V = 5 S.F
0.00030 = 5 S.F

2019
Resolution or Discrimination: The smallest detectable incremental
change of the input parameter that can be detected in the output
signal. Eg; Scale, Multi range meters.
Sensitivity: For an instrument or sensor with input x and output y.
Sensitivity = dy/dx
output
Input Input
output
Static sensitivity = Infinitesimal change in output /infinitesimal
change in input

2019
 Repeatability: Closeness of output reading when the same input is applied
repeatedly over a short period of time with the same measurement conditions
, same instrument and observer , same location and same conditions od use
maintained throughout.
 Reproducibility: Closeness of output readings for the same input when
there are changes in method of measurement , observer, location , conditions
of use, and time of measurement.
 Span & Range:
Range : High measurement possible
Span : Difference between max. and min measurement possible
E.g. Thermocouple (700 0C to 1200 0C)
Ammeter (0 to 10 A)
 Dead zone : The largest of a measured variable for which the instrument
does not respond Cause: friction in mechanical measurement system

2019
 Dead Time :The time before the instrument begins to respond after the measured
quantity has been changed. E.g: Camera, Data acquisition card, Ammeter

2019
 Drift : It is an undesired gradual departure of the instrument o/p over a period of
time that is unrelated to changes in i/p , operating conditions or load.
The drift may be caused by the following factors:
1) Mechanical vibrations
2) Temp. changes
3) Wear and Tear etc.
Classification:
1) Zero drift : If the whole of instrument calibration/ characterstics gradually shifts
one by same amount. It may be due to presence set or slippage and can be
corrected by shifting pointer position.
output
Zero
Normal characteristics
Characteristics with zero drift

2019
2) Span or senstivtity Drift : If the calibration from zero upwards changes
proportionally
output
Span drift
3) Zonal Drift : When the drift occurs only over a portion of span of an instrument.
output
zonal drift

2019
 Linearity: If the calibration from zero upwards changes proportionally.
If input-output relationship is a straight line passing through origin
• Nonlinearity cause lot of problem during signal conditioning even though it is more
accurate in some cases e.g. LVDT (linear) , Thermistor (Non-linear)
output
Input
Idealised St. Line
Actual calibration curve
Any departure from straight line relationship is non-linearity

2019
 Error: Error is the degree to which a measurement conforms to the expected or
true value .Errors are due to measuring instruments (causing the change in the
value of the parameter being measured) or due to persons carrying out the
measurements (human errors).Errors may be expressed as absolute or
percentage.
Types of Errors
 Gross errors
- Human errors
 Systematic errors
- Instrument errors
- Environmental errors
- Observational errors
Random errors

2019
 Error: Error is the degree to which a measurement conforms to the expected or
true value .Errors are due to measuring instruments (causing the change in the
value of the parameter being measured) or due to persons carrying out the
measurements (human errors).Errors may be expressed as absolute or
percentage.
Types of Errors
 Gross errors
- Human errors
 Systematic errors
- Instrument errors
- Environmental errors
- Observational errors
 Random errors

Errors in Measurement
2019
Static Error/Absolute Error- It is defined as the difference between the measured value and
the true value of the quantity. Then:
∆ A= Am-At (1)
Where ∆ A= error
Am = measured value of quantity
At = True value of quantity
∆ A is also absolute static error of quantity A
we have ɛ0 = ∆ A (2)
Where ɛ0 = absolute static error of quantity A
Relative Static Error
ɛr = absolute error/ true value (3)
= ∆ A/ At
= ɛ0 /At
Percentage static error % ɛr = ɛr x 100 (4)
We have At = Am - ∆ A
= Am - ɛ0 = Am - ɛr At = Am/(1+ ɛr ) (5)

Errors in Measurement
2019
Equation (5) can also be written as
At =Am (1- ɛr) (6)
Static Correction
∆ C= At -Am (7)

Question
2019
1. Which of the following instrument is more quality instrument.
Instrument A Instrument B
∆ A= 1 A ∆ A= 10 A
At = 2 amp At= 1000 amp
a) Only A
b) Only B
c) Both A and B
d) None of above

Errors in sum and Difference of
Quantities
2019
Error in the sum of quantities
equal the sum of absolute errors
Error in the difference of quantities
equal the sum of absolute errors

Errors in product and Quotient of
Quantities
2019

Dynamic Characteristics
2019
1) Speed of Response: It is defined as the rapidity with which a measurement
system responds to changes in the measurement quantity.
2) Measurement Lag: It refers to retardation or delay in the response of
measurement system to changes in measured quantity . The lag is caused by
conditions such as capacitance, inertia or resistance.
Measuring lag are of two types:
a) Retardation type lag
b) Time delay type lag
3) Fidelity: It is defined as the degree to which a measurement system indicates
changes in the measured quantity without any dynamic error.
4) Dynamic error or measurement error : It is the difference between true value of
the quantity changes with time and the value indicated by the measurement system
if no static error is assumed.

Numericals
2019
 The output voltage of a 5 V DC supply is measured as 4.9 V. Find (1) Absolute error (2)
Percent error (3) Relative accuracy and (4) Percent accuracy
 The three resistors R1 , R2 and R3 have the following ratings:
R1= 25Ω± 4 %
R2= 65Ω± 4%
R3= 45Ω± 4%
Determine the following
a) Limiting value of resultant resistance
b) % Limiting error of series combinations of resistance.

 AC and DC bridges
2019
 Bridges circuit are used for measuring components such as R, L and C and other circuit
parameters derived from component values such as frequency, phase angle and
temperature.
 Operate on a null indication principle (Comparison). That is known (standard) value is
adjusted until it is equal to unknown value
 Very high degrees of accuracy can be achieved using the bridges
Types of Bridge Circuits used in the Measurement
DC Bridges
 Low Resistance Measurement High Resistance Measurement
Ammeter Voltmeter method Direct Deflection Method
Kelvin Double Bridge Method Loss of Charge Method
Potentiometer method Megohm Bridge
 Medium Resistance Measurement Meggar
Ammeter voltmeter method
Substitution Method
Wheatstone bridge method

AC bridges
2019
Self Inductance Capacitance
Mutual Inductance
Frequency
 Maxwell’s Bridge
Maxwell inductance bridge
Maxwell inductance capacitance bridge
 Hay’s Bridge
 Anderson Bridge
 Owen’s Bridge
 De sauty’s Bridge
 Schering Bridge
 Carry Foster
Haydweiller bridge
 Wien’s Bridge

Ammeter Voltmeter Method
2019
 Resistance can be measured using Ammeter and Voltmeter and Applying ohms law.
 When voltmeter is connected across supply then resistance R= (E+Ev)/I
In both cases measured value of unknown resistance is equal to the reading of voltmeter
divided by reading of ammeter.
From fig.(1) R = Rm (𝟏 − 𝑹 𝒂/ 𝑹 𝒎 )
Ideally R = Rm only when Ra = 0
From fig.(2)
R = 𝑹 𝒎 /(𝟏− 𝑹 𝒎/ 𝑹 𝒗 )
Ideally R = Rm when resistance of voltmeter is ‘∞

Substitution Method
 Accuracy depends on the EMF of the battery and also depends on the resistance of the
circuit other than R & S
 Substitution method is more accurate than ammeter voltmeter method

Wheatstone Bridge
2019
• R1 and R2 are called the ratio arms.
• R3 is called the standard arm containing the standard known resistance.
• R4 is the unknown resistance to be measured.
• Battery connected between A and C.
• Galvanometer attached between B and D.

Balanced Condition
2019

Wheatstone Bridge
2019

Sensitivity
2019
Current Sensitivity:-
Voltage Sensitivity:-
Bridge Sensitivity:-

Under small Unbalance Condition
2019

Thevenin Voltage
2019

Sensitivity under unbalanec
2019

Errors in Wheatstone Bridge
2019
The difference between the true and the mark value of the three
resistances can cause the error in measurement.
The galvanometer is less sensitive. Thus, inaccuracy occurs in the
balance point.
The resistance of the bridge changes because of the self-heating which
generates an error.
The thermal emf cause serious trouble in the measurement of low-
value resistance.
The personal error occurs in the galvanometer by taking the reading or
by finding the null point.

Kelvin Bridge
2019

Kelvin Double Bridge
2019

Measurement of High Resistance
2019
Loss of Charge Method
Direct Deflection Method
Meggar
Megohm Bridge Method

Loss of Charge Method
Construction:
 R, an unknown resistance is connected in parallel with a capacitor C and electrostatic
voltmeter.
 A battery with emf V in parallel with R and C.
Operation:
 Capacitor is charged to suitable voltage by battery.
 Then allowed to discharge through resistance.
 Terminal voltage is observed over a considerable period of time during discharge.
 After application of voltage, Voltage across capacitor at any instant ‗t‘

Loss of Charge Method
Results:
 If R is very large, time for appreciable fall in voltage is very large.
 Care is to be taken while measuring V and v i.e. voltage at beginning and end of time ‗t‘
 Error in V/v
 Better results by change in voltage (V-v) directly and calculating R as

Direct Deflection Method
Cable having Sheath
Cable having no conducting Sheath

Measurement of volume and surface
resistivity

AC Bridges
The ac bridge is a natural out growth of the Wheatstone bridge.
The four arms is impedance. The battery and galvanometer are
replaced by an ac source and a detector sensitive to small alternating
potential difference.
Detectors commonly used are:
Head phones
Vibration galvanometer
Tunable amplifies detector.
Headphones widely used as detectors at frequency of 250 Hz and
above up to 3 or 4kHz. Vibration galvanometer at frequency 5 Hz to
1000 Hz .commonly used below 200 Hz.

General AC Bridge
•When the four resistive arms of the basic Wheatstone bridge are replaced
by impedances and the bridge is excited by an AC source, the result is an
AC Bridge.
•To balance the bridge, two conditions must be satisfied, the resistive (R)
and the reactive components (XC or XL). Once balanced, the AC Bridge
indicates a null.
•AC bridge circuits are also used for shifting phase, providing feedback
paths for oscillators and amplifiers, filtering out undesired signals, and
measuring the frequency of audio and radio frequency (RF) signals.

General AC Bridge
Bridge balance condition
In admittance form
Polar form of impedance
Sub. The polar values in balance
condition

Maxwell Inductance-Capacitance
Bridge

Bridge
Quality Factor

Bridge
Disadvantage:
Maxwell bridge is that, they are unsuitable of measuring the
low and high quality factor coils.

Anderson Bridge
•Need of Anderson's bridge though we have Maxwell bridge to measure quality factor
of the circuit.
•The main disadvantage of using Maxwell bridge is that, they are unsuitable of
measuring the low and high quality factor.
•However Maxwell bridge are suitable for measuring accurately medium quality factor
respectively.
•So, there is need of bridge which can measure low quality factor and this bridge is
modified Maxwell's bridge and known as Anderson's bridge.

Schering Bridge
This bridge is used to measure to the capacitance of the capacitor,
dissipation factor and measurement of relative permittivity.

Schering Bridge
Balance equation

Desauty’s Bridge
 The De Sauty’s bridge is an A.C Bridge works on the principle of Wheat stone’s bridge
 This bridge is used to determine the capacity of an unknown capacitor C1 in terms of a standard
known capacitor C2.

Owens Bridge
 It is used for the measurement of inductance and is expressed in terms of capacitance.

Owens Bridge
Advantages
 Balance equations are simple and does
not contain any frequency component.
 Can be used over a wide range of
frequencies.
Disadvantages
 Variable Capacitor is expensive.
 C2 tends to become large when
measuring high Q values.

Weins Bridge
• It is primarily known as frequency determining bridge.
• The bridge is also used in a harmonic distortion analyzer, as a Notch filter, and in audio
frequency and radio frequency oscillators as a frequency determining element.

Temperature Measurement
The International Practical Temperature Scale (IPTS) defines six primary
fixed points for reference temperatures in terms of:
 The triple point of equilibrium hydrogen 259.34C
 The boiling point of oxygen 182.962C
 The boiling point of water 100.0C
 The freezing point of zinc 419.58C
 The freezing point of silver 961.93C
 The freezing point of gold 1064.43C
(all at standard atmospheric pressure)
The freezing points of certain other metals are also used as secondary
fixed points to provide additional reference points during calibration
procedures.
140
Temperature Measurement

Instruments to measure temperature can be divided into separate
classes according to the physical principle on which they operate.
The main principles used are:
 The thermoelectric effect
 Resistance change
 Sensitivity of semiconductor device
 Radiative heat emission
 Thermography
 Thermal expansion
 Resonant frequency change
 Sensitivity of fibre optic devices
 Acoustic thermometry
 Colour change
 Change of state of material. 141

Disk Type (10mm)
143
Thermistors
Bead Type (0.15 mm)
Rod Type
4mm dia
12.5-50mmlong
Washer Type
Thermistor (Thermally sensitive
Resistor)

THERMally sensitive resISTOR
144
Thermistor Example

RTD , Thermistor & Thermocouple
145

146
Thermocouple Connection Current through Two Dissimilar Metals
V = α(Th - Tc) Seebeck Effect Circuit
Thermocouple

Seebeck effect & Peltier effect
147
Thermocouple

Thermocouple
O/p Voltage Vs Temperature
149

Thermocouple Compensation Circuits
151
Type T
Cold Junction CompensationType K

152
Type J Thermocouple using
Isothermal Block

153
Reference Junction Compensation
Reference Junction
Compensation

Thermopiles
T Srinivasa Rao Electronic Measurements and
Instrumentation (EC-315)
154
Multiple-junction thermocouple circuit designed to amplify the output of the
circuit

Different Types of Thermocouples
156

Advantages and Disadvantages of
Thermocouples
 Wide temperature range (-270oC to 2700oC
 Rugged Construction
 Bridge Circuits not required for temperature measurement.
 Comparatively cheaper in cost
 Good reproducibility
 Speed of response is high compared to thermometer systems.
 Calibration checks can be easily performed
 Using extension leads and compensating cables, long distance transmission for
temperature measurement is possible.
 Good Accuracy
 Compensation circuits is essential for accurate measurements
 They exhibit non-linearity in the emf versus temperature characteristics.
 Many applications needs signal amplifications.
 Proper separation of extension leads from thermocouple is required to avoid stray
electrical signal pickup. 157

158
• Pyrometry is a technique for measuring temperature
without physical contact.
• It depends upon the relationship between the temperature
of hot body and eletromagnetic radiation emitted by the
body.
• It is a technique for determining a body’s temperature by
measuring its eletromagnetic radiation .
• Pyro’ is the ‘Greek’ word which means fire.
Radiation Pyrometers

159
• Two types of pyrometers used in industries :
Radiation Pyrometers Optical Pyrometers

• A pyrometer has an optical system and detector. The
optical system focuses the thermal radiation onto the
detector. The output signal of the detector(Temperature T)
is related to the thermal radiation or irradiance j * of the
target object through the Stefan–Boltzmann law, the
constant of proportionality, called the Stefan Boltzmann
constant and the emissivity ε of the object.
Principle

• The radiation pyrometer has an optical system, including a lens, a mirror and
an adjustable eye piece. The heat energy emitted from the hot body is passed
on to the optical lens, which collects it and is focused on to the detector with
the help of the mirror and eye piece arrangement. The detector may either be a
thermistor or photomultiplier tubes. Though the latter is known for faster
detection of fast moving objects, the former may be used for small scale
applications. Thus, the heat energy is converted to its corresponding electrical
signal by the detector and is sent to the output temperature display device.
Working

Construction and Working
1.An eye piece at the left side and an optical lens on the right.
2.A reference lamp, which is powered with the help of a battery.
3.A rheostat to change the current and hence the brightness intensity.
4.So as to increase the temperature range which is to be measured, an absorption screen is
fitted between the optical lens and the reference bulb.
5.A red filter placed between the eye piece and the reference bulb helps in narrowing the
band of wavelength.
Working
The radiation from the source is emitted and the optical objective lens captures it. The lens
helps in focusing the thermal radiation on to the reference bulb. The observer watches the
process through the eye piece and corrects it in such a manner that the reference lamp
filament has a sharp focus and the filament is super-imposed on the temperature source
image. The observer starts changing the rheostat values and the current in the reference
lamp changes. This in turn, changes its intensity. This change in current can be observed in
three different ways.
1. The filament is dark. That is, cooler than the temperature source.
2. Filamnet is bright. That is, hotter than the temperature source.
3. Filament disappears. Thus, there is equal brightness between the filament and
temperature source. At this time, the current that flows in the reference lamp is measured,
as its value is a measure of the temperature of the radiated light in the temperature source,
when calibrated.
Construction and Working

• ABILITY TO MEASURE HIGH TEMP
• NO NEED FOR PHYSICAL CONTACT
• FAST RESPONSE SPEED
• HIGH O/P
• MODERATE COST
Disadvantages

• Emissivity errors are introduced
• Errors due to the absorption of radiation by
carbon dioxide, water or other apparently
transparent gases.
Disadvantages

• They are used for temperatures above the practical operating range of
thermocouples.
• They can be used in the environments which contaminate or limit the
life of thermocouple.
• Used for moving targets.
• They are used for measurement of average temperature of large
surface areas.
• They are used for the targets which would be damaged by contact with
primary elements like thermocouples and resistance thermometers.
Applications

Pressure Measurement
It is defined as force/unit area. Pressure are exerted by gases, vapours and liquids.
Units of psi, mm Hg and kPa
Atmospheric Pressure
It is the pressure that an area experience due to force exerted by the atmosphere. The
atmospheric pressure at sea level ( above absolute zero) called std. atmospheric pressure.
Gauge Pressure
It is measured with the help of pressure measuring instrument in which atmospheric
pressure is taken at datum. Gauge pressure record above or below atmospheric pressure.
Absolute pressure
Any pressure above the absolute zero of pressure. The actual pressure at given position.
Absolute pressure= Atmospheric +gauge pressure
Vacuum pressure= Atmospheric pressure+ Absolute pressure

Positive gauge pressure
Negative gauge pressure or vacuum
Atmospheric pressure
Zero absolute pressure
Absolute pressure

Static pressure (Ps)
It is defined as force/ unit area acting on the wall by a fluid at rest or flowing parallel to
the wall in a pipeline.
Total or Stagnation Pressure (Pt)
It is defined as the pressure that would be obtained if the fluid stream were brought to rest
isentropically.
For an incompressible fluid or gas flowing at low velocities.
Dynamic pressure =
𝑉2
2𝑔
Total = static + dynamic
Pt= Ps+
𝑉2
2𝑔

Pressure Measuring Instruments
 Low Pressure Measurement (below 1 mm of Hg)
- Manometers
- Low pressure gauges
 Medium and High Pressure (b/w 1mm of Hg to 1000 atm)
- Bourdon Tubes
- Diaphragm
- Bellow pressure gauges
- Dead Weight pressure gauge
 Low Vacuum and Ultra High Vacuum (760 Torr to 10^-9 Torr and beyond)
- Mcleod. Gauge
- Thermal Conductivity
- Ionisation Gauges
 Very High Pressure (1000 atm. and above)
- Diaphragm gauges
- Electrical resistance pressure gauges

Two methods for the measurement of low pressure
 Direct Method : Here the displacement deflection caused by the pressure is
measured and is correlated to pressure
- Spiral Bourdon tubes
- Flat and Corrugated Diaphragms
- Capsules
- Manometers
 Indirect Method : In these methods , pressure is determined through the
measurement of certain other pressure controlled properties including volume and
thermal conductivity.
- Mcleod. Gauge
- Thermal conductivity gauges
- Ionisation gauges
- Radioactive vacuum meters

Manometers
• Simplest form is U-shaped, liquid filled tube
• Reference and measured pressure applied to ends of tube
• Difference in pressure causes difference in liquid level between sides
Principles: Hydrostatic Law
∆P=ρ g h

Applications, Advantages and Disadvantages
Mainly spot checks or calibration
– Modern calibration using electronic meters
• Low range measurements
– Higher measurements require mercury
- toxic, therefore hazardous
- Advantages
Simple operation and Construction
Inexpensive
Disadvantages
Range (water)
Higher pressure range requires mercury
Readings are localised

Sensing Elements
The main types of sensing elements are
•Bourdon tubes
•diaphragms
•bellows
The basic pressure sensing element can be configured as a C-shaped Bourdon tube
(A); a helical Bourdon tube (B); flat diaphragm
(C); a convoluted diaphragm (D); a capsule (E); or a set of bellows (F).

Bellows
• Bellows sensor is an axially flexible, cylindrical enclosure with folded sides. When
pressure is applied through an opening, the closed end extends axially.
• Bellows elements can measure absolute pressure, gauge pressure, vacuum, or differential
pressure.

Bourdon Tubes
• A Bourdon gauge uses a coiled tube, which, as it expands due to pressure
increase causes a rotation of an arm connected to the tube.
• bourdon are often used in harsh environments and high pressures, but can also be used
for very low pressures; the response time however, is slower than the bellows or
diaphragm.
C-type bourdon
psi Range as low as 0 - 15 psi up to 0-1500
Helical bourdon
Range as low as 0 - 200 psi up to 0 – 6000 psi
Spiral bourdon
.Range as low as 0-10 psi up to 0-100,000 psi

Diaphragms
• A diaphragm is a circular-shaped convoluted membrane that is attached to the pressure fixture
around the circumference . The pressure medium is on one side and the indication medium is on
the other.
• Diaphragms provide fast acting and accurate pressure indication. However, the movement or
stroke is not as large as the bellows .

Electrical Transducers as Secondary Transducers
Resistance Type
Inductive Type
Capacitive Pressure Transducer
Differential Transformer (LVDT)
Photoelectric

Indirect method for the measurement of pressure
 Pirani Gauge
 Thermocouple vaccum gauge
 Ionisation gauges
 McLeod Gauges
 Dead Weight Tester
Knudsen Gauges

Applications, Advantages and Disadvantages
Applications: It is used to calibrated all kinds of pressure gauges such as industrial pressure
gauges, engine indicators and piezoelectric transducers.
Advantages: it is simple in construction and easy to use. It can be used to calibrated a wide
range of pressure measuring devices. Fluid pressure can be easily varied by adding weights
or by changing the piston cylinder combination.
Limitations: the accuracy of the dead weight tester is affected due to the friction between
the piston and cylinder, and due to the uncertainty of the value of gravitational constant 'g'

Stroboscope ( Measurement of Angular Velocity)
This method measures the periodic or rotary motions by a device called a
STROBOSCOPE.
• This instrument is a simple and manually operated device.
• The speed is measured by adjusting the receptor frequency so that the moving
section is visible at a particular time interval.
Principle
The receptor circuit is based upon variable frequency oscillator which controls the
flashing frequency.
• A strong light is flashed on a moving object , at the time each flash occurs , in an
instantaneous position , the object will appear to be stationary

Stroboscope ( Measurement of Angular Velocity)
A strobotron is the high frequency source of light whose frequency can be varied and
controlled.
• For measuring the speed of shaft , a mark is made on the disc attached to the shaft.
• The flashing frequency is adjusted until the mark appears stationary.
• The flashing rate is reduced gradually and the flashing frequencies are noted for all
single line images.

Advantages
Advantages
• Imposes no load on the shaft hence no power loss.
• Non contact type hence, no attachments needed.
• Convenient to use for spot checks on machinery speeds and laboratory work.

Electronic Measurement and Instrumentation

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