Cochin University of Science and Techology (CUST) 2007-1st Year B.Tech Electrical and Electronics Engineering electrical measurements and measuring instruments - Question Paper

FIRST TERMINAL exam

ELECTRICAL MEASUREMENTS AND MEASURING INSTRUMENTS

1. a) describe the terms precision, linearity, hysteresis, noise factor and noise figure.

b) discuss the term sensitivity of a dc bridge.

c) Derive the condition for an ac bridge to be balanced.

d) discuss how a potentiometer can be used for the measurement of power and
resistance.

2. a) discuss the various static characteristics of a measurement system.

b) A highly sensitive galvanometer can detect a current as low as 0.1nA. This
galvanometer is used in a Wheatstone bridge as a detector. The resistance of
galvanometer is negligible. every arm of the bridge has a resistance of 1kilo ohm.
The input voltage applied to the bridge is 20V. compute the smallest change in
resistance that can be detected. The resistance of galvanometer can be neglected as
compared with internal resistance of bridge.

OR

3. a) Derive an expression for measurement of an unknown resistance using Carry Foster
slide wire bridge.

b) A 4 terminal resistor of approximately 50 micro ohm resistance was measured by
means of a Kelvin bridge having the subsequent component resistances. A standard
resistance 100.03 micro ohm, inner ratio arms 100.31ohm and 200ohm, outer ratio
arms 100.24ohm and 200ohm, resistance of link connecting the standard and the
unknown resistance is 700 micro ohm. compute unknown resistance to the closest
0.01ohm.

4. a) define the Murray loop test for localization of ground & short circuit fault in
cables.

b) discuss with a neat diagram the working of Vernier Potentiometer.

OR

5. a) Derive the formula of balance of an Anderson’s bridge. Draw the phasor diagram
for balance condition. elaborate the advantages of Anderson’s bridge?

b) What is meant by standardisation of a dc potentiometer? define the procedure of
standardisaton.

Earning:   Approval pending.