Solution for Electrical and Electronic Measurements

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1 Q.1) Solution for Electrical and Electronic Measurements May 2016 Index a). 2 b). 2 c). 3-4 d). 5-6 e).. 6 Q.2) a) b) Q.3) a) b) Q.4) a) b) Q.5) a). N.A b) Q.6) a) b) c) d)

2 Q1) Ans: (a) Differentiate between indicating and integrating instrument. Ans: (b) Explain the resolution and sensitivity of digital meter. 2

3 Ans: (c) Explain piezo electrical transducer Different modes of piezoelectric transducer. A B 3

4 Piezoelectric transducer. 4

5 Ans: (d) Explain a suitable bridge to measure medium resistance. 5

6 Ans: (e) Differentiate between Active and Passive transducers 6

7 Q2 Ans: (a) Explain working principle,construction of D.C permanent. Magnet moving coil type meter and hence derive the torque equation. 7

8 In order to obtain longer movement of the pointer and a longer angular swing of the coil, a concentric magnet construction shown in the figure is used. Since magnet is concentric type,it produces a radial flux pattern which extends over or more.this type of construction is used for many panel type and some portable instruments. In recent years, the magnetic system shown in the figure is developed.it uses magnetic material like Alnico.In this system the magnet itself serves as the core.the moving coil moves over the magnet.the active sides of the moving coil are located in the uniform radial field between the pole pieces and steel yoke. This system has advantages of being unaffected by the external magnetic fields.it also eliminates the magnetic shunning effects and needs for magnetic shielding in the form of iron cases. 8

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11 (b) Describe construction, working principle,and theory of dyno meter Type of wattmeter. Ans: 11

12 12

13 TORQUE EQUATION: 13

14 14

15 If the position of zero mutual inductance is at the mid-scale,the scale will will be uniform over 80 0 to which covers almost the entire scale range. ERRORS IN ELECTRODYNAMOMETER: 15

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17 Q3 Ans: (a) Explain the block diagram Ramp type digital voltmeter. BLOCK DIAGRAM OF LINEAR RAMP TYPE DVM 17

18 The sample rate multivibrator determines the rate of measurement cycle.the oscillation of the multivibrator is usually adjusted by a front panel control named RATE,from few cycles per second to as high a 1000 cycles per second.the typical value is 5 cycles/second with the accuracy of ± 0.005% of the reading 18

19 STAIR CASE RAMP TYPE DVM Basic Principle : The basic principle is that the input signal is compared with internally generated voltages which is increased in steps starting from zero. The number of pulses counted by the counter in the time interval which staircase voltage takes to reach unknown input voltage is displayed as the ouput. The figure above represents DVM 19

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21 (b) Explain Kelvin s double bridge to measure low resistance and hence derive the equation of unknown resistance using the above bridge. Ans: 21

22 The known resistance R 3 is adjusted such that galvanometer indicates zero and then using Equation R x can be calculated. Advantages 1) In a typical Kelvin s double bridge the range of resistance covered is 1Ω to 10µΩ with an accuracy of ± 0.05% to ± 0.2%. 2) The resistance of the connecting lead R y has no effect on measurement 22

23 Q4 Ans: (a) Explain the Maxwell s induction bridge to measure self induction and hence derive the equation self induction using the above bridge draw the phasor diagram. 23

24 (4) It is useful for measurement of a wide range of inductance at power And audio frequencies (5) It can measure inductance from 1 H to 1000 H with ± 2 % error. 24

25 Ans: (b) Explain the construction and working of D.C. Crompton type of potentiometer. 25

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27 Q5 (a) A moving coil instruments give a full scale deflection pf 10mA when the potential difference across its terminal is 100mV. Calculate. i) Shunt resistance for a full scale deflection corresponding to 100A. ii) The series resistance for full scale reading 100V. Calculate the power dissipation for each. Ans: N.A 27

Ans: (b) Explain the construction and working of LVDT. It is a variable inductance displacement transducer.the construction of LVDT is as shown in fig.

28 Ans: (b) Explain the construction and working of LVDT. It is a variable inductance displacement transducer.the construction of LVDT is as shown in fig. CONSTRUCTION OF LVDT The two secondary winding are connected in series opposition as shown in fig. (a).hence the voltage induced into these windings are of opposite polarities. 28

29 The output voltage is given by, 29

30 Performance characteristics of LVDT (vi) Dynamic response: This indicates how fast the LVDT responds to the displacement of the 30

31 Core. Dynamic response is dependent on the excitation frequency and the core weight. Advantages of LVDT Q6 Write short note on any three Ans: (a) Moving iron instrument 31

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33 Repulsion type moving iron instrument 33

34 Ans: (b) Megger MEGGER CIRCUIT 34

35 Ans: (c) Tachometer PHOTOELECTRIC TACHOMETER 35

36 VARIABLE RELUCTANCE TACHOMETER 36

37 (d) Reed moving coil type frequency meter: Ans: 37

38 CONSTRUCTION AND WORKING: 38

Bhoj Reddy Engineering College for Women, Hyderabad Department of Electronics and Communication Engineering Electrical and Electronics Instrumentation

Bhoj Reddy Engineering College for Women, Hyderabad Department of Electronics and Communication Engineering Electrical and Electronics Instrumentation Academic Year: 2016-17 III B Tech II Semester Branch: