electrical measurements and lecture notes on electrical measurements and instrumentation 2018...
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2018 – 2019
II B. Tech I Semester (R17)
Ms. Y.HARIKRISHNA, Assistant Professor
CHADALAWADA RAMANAMMA ENGINEERING COLLEGE (AUTONOMOUS)
Chadalawada Nagar, Renigunta Road, Tirupati – 517 506
Department of Electronics and Communication Engineering
ELECTRICAL MEASUREMENTS AND INSTRUMENTATION
III Semester: EEE
Course Code Category Hours / Week Credits Maximum Marks
17CA02303 Core L T P C CIA SEE Total
3 - - 3 30 70 100
Contact Classes: 51 Tutorial Classes:
Nil Practical Classes: Nil Total Classes: 51
The course should enable the students to:
I. Demonstrate the principle, working of electrical measurement instruments.
II. Illustrate the principles of energy measurement in electrical loads.
III. Outline the use of cathode ray oscilloscope.
IV. Evaluate various transducers for electrical measurements.
UNIT - I INTRODUCTION TO ANALOG MEASURING INSTRUMENTS Classes:11
Classification – Ammeters and Voltmeters – PMMC, Dynamometer, Moving Iron Type
Instruments Single Phase Dynamometer Wattmeter Double Element and Three Element
Dynamometer Wattmeter. Single Phase Induction Type Energy Meter . Three Phase Energy Meter.
(Principle and working only)
UNIT - II INTRODUCTION TO DIGITAL MEASURING INSTRUMENTS Classes:10
Current Transformers and Potential Transformers Ratio and Phase Angle Errors. Potentiometers:
Principle and Operation of D.C. Crompton’s Potentiometer
Introduction to digital Measurements Digital Voltmeters - Successive Approximation, Ramp and
Integrating Type-Digital Frequency Meter-Digital Multi meter-Digital Tachometer
UNIT -III OSCILLOSCOPES AND BRIDGES Classes: 10
Oscilloscopes: CRO, CRT features, derivation of deflection sensitivity Measurement of amplitude,
frequency and phase (Lissajous method).
DC Bridges: Wheatstone bridge, Wein Bridge Kelvin Bridge, AC bridges: Measurement of
inductance-Maxwell’s bridge, Anderson Bridge. Measurement of capacitance- Schearing Bridge
.Measurement of low medium high resistance methods
UNIT - IV INTRODUCTION TO TRANSDUCERS Classes:10
Definition of Transducers. Principle of Operation of Resistive, Inductive, Capacitive Transducers,
LVDT, Strain Gauge and Its Principle of Operation, Gauge Factor, Thermistors, Thermocouples,
piezoelectric Transducers, Photovoltaic, Photo Conductive Cells, Photo Diodes
Measurement of Displacement, Velocity, Angular Velocity, Acceleration, Force, Torque,
Temperature, Pressure, Flow, Liquid level.(any two methods)
UNIT - V INDUSTRIAL ENERGY MEASUREMENT METHODS Classes: 10
Static /microprocessor based Energy meter,multi function meters, Industrial energy
measurement methods-low voltage high current, high voltage high current . Concept of
Theft of energy detection -Energy consumption when voltage coil reversed, current coil
reversed. Energy consumption when CT ratio changes.
1. A K Sawhney, “Electrical and Electronic measurement and instruments”, Dhanpat Rai and Sons
2. E W Golding and F C Widdis, “Electrical measurements and measuring instruments” wheeler
publishing. 5th Edition.
3. J.B. Gupta “A Course in Electrical and Electronic Measurements & Instrumentation” SK
Kataria and Son’s, 14th Edition
1. Buckingham and Price, “Electrical measurements”, Prentice Hall.
2. D V S Murthy, “Transducers and Instrumentation”, Prentice Hall of India, 2nd Edition, 2009.
3. A S Morris, “Principles of measurement of instrumentation”, Pearson/Prentice Hall of India, 2nd
4. H S Kalsi, “Electronic Instrumentation”, Tata McGrawHill Edition, 1st Edition 1995.
https://www.amazon.in/J.B.-Gupta/e/B00JOIBJBI/ref=dp_byline_cont_book_1 https://www.crectirupati.com/ https://www.bookboon.com/en/mechanics
At the end of the course a student will be able to:
1. Use wattmeters, pf meters, and energy meters in a given circuit and extend the range of
ammeters and voltmeters, analyze periodic, and aperiodic signals using CRO.
2. Measure active power, and energy both 1-phaseand 3-phase circuits
3. Determine the resistance values of various ranges, L and C values using appropriate
4. Use CTs and PTs for measurement of very large currents and high voltages and evaluate
various transducers for electrical measurements.
5. Energy measurement methods for Industrial loads
6. Measurement of non electrical quantities using transducers
INTRODUCTION TO ELECTRICAL MEASUREMENTS
PERMANENT MAGNET MOVING COIL INSTRUMENTS:
These instruments are employed either as ammeters or voltmeters and can be used for d.c work
Principle of Permanent magnet moving coil instruments:
This type of instrument is based on the principle that when a current carrying conductor is placed in
a magnetic field, mechanical force acts on the conductor. The coil placed in magnetic field and
carrying operating current is attached to the moving system. With the movement of the coil the
pointer moves over the scale.
Construction of Permanent magnet moving coil instruments:
It consists of a powerful permanent magnet with soft iron pieces and light rectangular coil of many
turns of fine wire wound on aluminium former inside which is an iron core as shown in fig. The
purpose of coil is to make the field uniform. The coil is mounted on the spindle and acts as the
moving element. The current is led into and out of the coil by means of the to control hair springs,
one above and the other below the coil. The springs also provides the controlling torque. Eddy
current damping is provided by aluminium former.
Permanent magnet moving coil instrument
Working of Permanent magnet moving coil instruments:
When the instrument is connected in the circuit, operating current flows through the coil. This
current coil is placed in the magnetic field produced by the permanent magnet and therefore,
mechanical force acts on the coil. As the coil attached to the moving system, the pointer moves
over the scale.
It maybe noted that if current direction is reversed, the torque will also be reversed since the
direction of the field of permanent magnet is same. Hence, the pointer will move in the opposite
direction, i.e it will go on the wrong side of zero. In other words, these instruments work only when
current in the circuit is passed in a definite direction i.e. for d.c circuit only.
It is worthwhile to mention here that such instruments are called permanent magnet moving coil
instruments because a coil moves in the field of a permanent magnet.
Deflecting torque of Permanent magnet moving coil instruments:
When current is passed through the coil, a deflection torque is produced due to the reaction
between permanent magnetic field and the magnetic field of the coil as shown in the fig.
Let B = flux density in the air gap between the magnetic poles and iron core.
l = active length of the coil side in meters.
N = number of turns of coil.
If a current of i amperes flows in the coil in the direction shown, then force F acting on each coil
side is given by
F = BI / N newtons
Td = Force * perpendicular distance
= F * 2r newton - meters
where r is the distance of coil side from the axis of rotation in meters
Td = NBIl * 2r newton - meters
If A ( = l * 2r) is the surface area of the coil, then
Td = NBIA newton - meters
Deflection torque = Ampere turns on coil (NI) * Area of coil (A) * flux density (B)
Td proportional I
Since the control by springs, therefore controlling torque is proportional to the angle of deflection
Tc proportional I
The pointer will come to rest at a position when,
Td = Tc
Deflection proportional I
Thus, the deflection is directly proportional to the operating current. Therefore, such instruments
have uniform scale.
Advantages of Permanent magnet moving coil instruments:
1. uniform scale.
2. Very ef