17-01-2013, 02:40 PM
Electrical & Electronics Measuring Instruments Question Paper
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Q.1 (a) Derive an expression for the resistance required in galvanometer circuit to make
it dead beat, assuming the damping to be entirely electromagnetic.
07
(b) Explain the special features incorporated in an electrodynamometer type
wattmeter so that it can be used for low power factor applications.
07
Q.2 (a) With a suitable circuit diagram explain the construction and write steps that are
used for measurement of unknown emf by Crompton’s potentiometer.
07
(b)
1. Explain the construction of a ballistic galvanometer. How can a ballistic
galvanometer be calibrated using a mutual inductance?
04
2. Measurements for the determination of the impedance of a coil are made on a
coordinate type of potentiometer. The results are :
Voltage across 1 Ω standard resistance in series with the coil + 0.952 V on
inphase dial and - 0.340 V on quadrature dial.
Voltage across 10:1 potential divider connected to the terminals of the coil:
+ 1.35 V on inphase dial and + 1.28 V on quadrature dial.
Calculate the resistance and reactance of the coil.
03
OR
(b) Explain the construction and operation of a Drysdale phase shifting transformer.
Obtain the necessary expression for the correct magnitudes and the phase
relationship in terms of circuit parameters.
07
Q.3 (a) Describe the construction and working of a PMMC instrument. Mention the
method of damping used in this instrument.
07
(b)
1. A moving coil instrument whose resistance is 25 Ω gives a full scale deflection
with a current of 1 mA. This instrument is to be used with a manganin shunt to
extend its range to 100 mA. Calculate the error caused by a 100 C rise in
temperature when :
(i) Copper moving coil is connected directly across the manganin shunt.
(ii) A 200 Ω manganin resistance is used in series with the instrument moving
coil.
The temperature co-efficient of copper is 0.004/ 0 C and that of manganin
0.00015/ 0 C.
04
2. Explain the method for measurement of reactive power in three phase circuit
using a single electrodynamometer type wattmeter.