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Electronics and Communication Engineering - Measurements and Instrumentation

Exercise : Measurements and Instrumentation - Section 2
31.
Consider the following operation in respect of Wheatstone bridge (Kb, denotes battery key, Kg denotes galvanometer key)
  1. open Kb
  2. close Kg
  3. close Kb
  4. open Kg
The correct sequence of operations is
1, 2, 3, 4
3, 1, 2, 4
4, 3, 2, 1
3, 2, 4, 1
Answer: Option
Explanation:

Battery key must be closed before galvanometer key. Moreover galvanometer key must be opened before battery key. This is to avoid damage to galvanometer.

32.
Two voltmeters 0-250 V each having resistances of 5 kΩ and 10 kΩ respectively and are connected in series. To ensure that neither of them goes beyond scale the total voltage which can be applied should be less than
500 V
400 V
375 V
250 V
Answer: Option
Explanation:

or V = 375 V.

33.
A 24 mm long conductor has a resistance of 128 Ω. The change in resistance is 13.3 Ω and change in length is 1.6 mm under tension. The gauge factor is
1.2
1.6
2.1
2.6
Answer: Option
Explanation:

.

34.
Measuring of unknown voltage with a dc potentiometer loses its advantage of open circuit measurement when
primary circuit battery is changed
standardisation is done to compensate for drift
voltage is larger than range of potentiometer
range reduction by factor of 10 is employed
Answer: Option
Explanation:

When volt ratio box is used to reduce range, the advantage of open-circuit measurement is lost.

35.
In a digital measuring device the input electrical signal is in the frequency range of dc to ac (50) Hz. It must be sampled at a rate of
f times/sec
0.5 f times/sec
0.25 f times/sec
2 f times/sec
Answer: Option
Explanation:

Sampling frequency must be twice the input frequency.

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