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  • LECTURE NOTES

    ON

    ELECTRICAL MEASUREMENTS

    AND INSTRUMENTATION

    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

    OBJECTIVES:

    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.

    Text Books:

    1. A K Sawhney, “Electrical and Electronic measurement and instruments”, Dhanpat Rai and Sons

    Publications.

    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

    Reference Books:

    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

    Edition, 1994.

    4. H S Kalsi, “Electronic Instrumentation”, Tata McGrawHill Edition, 1st Edition 1995.

    Web References:

    1. https://www.researchgate.net

    2. https://www.aar.faculty.asu.edu/classes/

    3. https://www.electrical4u.com

    4. https://efficientcarbon.com/wp-content/uploads/2013/07/Net-Metering-and-Solar-

    Rooftop_Whitepaper_EfficientCarbon.pdf

    5. https://www.conserve-energy-future.com/what-is-net-metering-and-how-net-metering-

    works.php

    6. https://www.electrical4u.com/digital-storage-oscilloscope/

    7. https://www.crectirupati.com

    E-Text Books:

    1. https://www.jntubook.com

    2. https://www.freeengineeringbooks.com

    3. https://www.bookboon.com/en/mechanics

    Course Outcomes:

    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

    bridges.

    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

  • UNIT 1

    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

    only.

    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.

    https://4.bp.blogspot.com/-cpsBSma2trc/V4sR9n14vWI/AAAAAAAABTU/cN4VYEZDUsw5DkVjnvDPaKukGJuRe7l5QCLcB/s1600/img112+-+Copy.jpg

  • 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

    i.e

    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

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