Electronics and Communication Engineering - Measurements and Instrumentation

36. 

Which of the following are needed both for protection and metering?

A. Wattmeters
B. Instrument transformers
C. Energy meters
D. Power factor meters

Answer: Option B

Explanation:

Instrument transformers are used to measure high currents and voltages. They also feed the relays for protection.


37. 

A digital frequency counter can be converted to DVM by addition of a suitable

A. voltage controlled oscillator
B. D/A converter
C. power amplifier
D. operational amplifier

Answer: Option B

Explanation:

D/A converter changes digital output to analog output.


38. 

A dynamometer wattmeter is connected in ac circuit. The reading will be

A. V-A product
B. average power
C. peak power
D. instantaneous power

Answer: Option B

Explanation:

Wattmeter measures average power over a cycle.


39. 

The speed transducer using a drag cup rotor has the main advantage of

A. very high accuracy
B. low energy requirement
C. cheap construction
D. all of the above

Answer: Option B

Explanation:

A drag cup rotor has low inertia. Therefore it requires little amount of energy.


40. 

A voltmeter using thermocouples measures

A. rms value
B. peak value
C. average value
D. peak to peak value

Answer: Option A

Explanation:

Since the thermocouple is based on heating effect, rms value is measured.