Note for Electrical Measurements - EM By JNTU Heroes

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CLASS NOTES ON ELECTRICAL MEASUREMENTS & INSTRUMENTATION 2015 CLASS NOTES ON ELECTRICAL MEASUREMENTS & INSTRUMENTATION 1

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CLASS NOTES ON ELECTRICAL MEASUREMENTS & INSTRUMENTATION 2015 DISCLAIMER This document does not claim any originality and cannot be used as a substitute for prescribed textbooks. The matter presented here is prepared by the author for their respective teaching assignments by referring the text books and reference books. Further, this document is not intended to be used for commercial purpose and the committee members are not accountable for any issues, legal or otherwise, arising out of use of this document. 2

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CLASS NOTES ON ELECTRICAL MEASUREMENTS & INSTRUMENTATION 2015 SYLLABUS ELECTRICAL MEASUREMENTS & INSTRUMENTATION (3-1-0) MODULE-I (10 HOURS) Measuring Instruments: Classification, Absolute and secondary instruments, indicating instruments, control, balancing and damping, constructional details, characteristics, errors in measurement, Ammeters, voltmeters: (DC/AC) PMMC, MI, Electrodynamometer type Wattmeters: Electrodynamometer type, induction type, single phase and three phase wattmeter, compensation, Energymeters: AC. Induction type siqgle phase and three phase energy meter, compensation, creep, error, testing, Frequency Meters: Vibrating reed type, electrical resonance type MODULE-II (10 HOURS) Instrument Transformers: Potential and current transformers, ratio and phase angle errors, phasor diagram, methods of minimizing errors; testing and applications. Galvanometers: General principle and performance equations of D' Arsonval Galvanometers, Vibration Galvanometer and Ballistic Galvanometer. Potentiometers: DC Potentiometer, Crompton potentiometer, construction, standardization, application. AC Potentiometer, Drysdale polar potentiometer; standardization, application. MODULE-III (10 HOURS) DC/AC Bridges :General equations for bridge balance, measurement of self inductance by Maxwell’s bridge (with variable inductance & variable capacitance), Hay’s bridge, Owen’s bridge, measurement of capacitance by Schearing bridge, errors, Wagner’s earthing device, Kelvin’s double bridge. Transducer: Strain Gauges, Thermistors, Thermocouples, Linear Variable Differential Transformer (LVDT), Capacitive Transducers, Peizo-Electric transducers, Optical Transducer, Torque meters, inductive torque transducers, electric tachometers, photo-electric tachometers, Hall Effect Transducer MODULE-IV (10 HOURS) CRO: Block diagram, Sweep generation, vertical amplifiers, use of CRG in measurement of frequency, phase, Amplitude and rise time of a pulse. Digital Multi-meter: Block diagram, principle of operation, Accuracy of measurement, Electronic Voltmeter: Transistor Voltmeter, Block diagram, principle of operation, various types of electronic voltmeter, Digital Frequency meter: Block diagram, principle of operation TEXT BOOKS [1]. A Course in Elec. & Electronics Measurements & Instrumentation: A K. Sawhney [2]. Modern Electronic Instrumentation and Measurement Techniques: Helfrick & Cooper [3]. Electrical Measurement and Measuring Instruments - Golding & Waddis 3

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CLASS NOTES ON ELECTRICAL MEASUREMENTS & INSTRUMENTATION 2015 MEASURING INSTRUMENTS 1.1 Definition of instruments An instrument is a device in which we can determine the magnitude or value of the quantity to be measured. The measuring quantity can be voltage, current, power and energy etc. Generally instruments are classified in to two categories. Instrument Absolute Instrument Secondary Instrument 1.2 Absolute instrument An absolute instrument determines the magnitude of the quantity to be measured in terms of the instrument parameter. This instrument is really used, because each time the value of the measuring quantities varies. So we have to calculate the magnitude of the measuring quantity, analytically which is time consuming. These types of instruments are suitable for laboratory use. Example: Tangent galvanometer. 1.3 Secondary instrument This instrument determines the value of the quantity to be measured directly. Generally these instruments are calibrated by comparing with another standard secondary instrument. Examples of such instruments are voltmeter, ammeter and wattmeter etc. Practically secondary instruments are suitable for measurement. Secondary instruments Indicating instruments Recording Integrating 9 Electromechanically Indicating instruments