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Chapter: Measurements and Instrumentation - Electrical and Electronics Instruments

Important Short Questions and Answers: Electrical and Electronics Instruments

Measurements and Instrumentation - Electrical and Electronics Instruments - Important Short Questions and Answers: Electrical and Electronics Instruments

ELECTRICAL AND ELECTRONIC INSTRUMENTS

 

1. Name the types of instruments used for making voltmeter and ammeter.

The types of instruments used for making voltmeter and ammeter are

i. PMMC type

ii. Moving iron type

iii. Dynamometer type

iv. Hot wire type

v. Electros tatic type

vi. Induction  type.

 

2.   State the advantages of PMMC instruments.

The advantages of PMMC instruments are:

i.    Uniform scale

ii.   No hysterisis loss

iii.  Very accurate

iv.  High efficiency

 

3.   State the disadvantages of PMMC instruments.

The disadvantages of PMMC instruments are

i.    Cannot be used for ac measurements

ii.   Some errors are caused by temperature variations

 

4.   State the applications of PMMC instruments.

 

The applications of PMMC instruments are i. Measurement of D.C voltage and current ii. Used in D.C galvanometer.

 

5. How the range of instrument can be extended in PMMC instruments?

The range of PMMC instrument can be extended by

i. connecting a shunt resistor

ii. connecting a series resistor.

 

6. State the advantages of dynamometer type instruments.

 

The advantages of dynamometer type instruments are

i. They Can be used for both D.C and A.C measurements

ii. Free from hysterisis and eddy current errors.

 

7. State the advantages of moving iron type instruments.

 

The advantages of moving iron type instruments are:

i. Less expensive

ii. Can be used for both DC and AC

iii.  Reasonably accurate.

 

8.   State the advantages of Hot wire type instruments.

 The advantages of Hot wire type instruments are:

i.    They can be used for both dc and ac

ii.   They are unaffected by stray magnetic fields

iii.  Readings are independent of frequency and waveform.

 

9.   What are the constructional parts of dynamometer type wattmeter?

The constructional parts of dynamometer type wattmeter are:

i.    Fixed coil

ii.   Moving Coil

iii.  Current limiting resister

iv. Helical spring

v.   Spindle attached with pointer

vi. Graduated scale

 

10. State the disadvantages of dynamometer type wattmeter.

The disadvantages of dynamometer type wattmeter are:

i.    Readings may be affected by stray magnetic fields.

ii.   At low power factor it causes error.

 

11. Name the errors caused in dynamometer type wattmeter.

The errors caused in dynamometer type wattmeter are:

i. Error due to pressure coil inductance

ii. Error due to pressure coil capacitance

iii. Error due to methods of connection

iv.  Error due to stray magnetic fields

v. Error due to eddy current.

 

12. Name the methods used for power measurement in three phase circuits.

 

The methods used for power measurement in three phase circuits are:

i. Single wattmeter method

 

ii. Two wattmeter method

 

iii.  Three wattmeter method.

 

13. What are the special features to be incorporated for LPF wattmeter?

The special features to be incorporate for LPF wattemeter are:

i.    Pressure coil circuit

ii.   Compensation for Pressure coil current

iii.  Compensation for Pressure coil inductance.

 

14. Name the methods used in wattmeter calibration.

The methods used in wattmeter calibration are:

i. Comparing with standard wattmeter.

ii. Using voltmeter ammeter method.

iii.  Using Potentiometer.

 

15. Name the constructional parts of induction type energy meter.

The constructional parts of induction type energymeter are:

i.    Current    coil with series   magnet       

ii. Voltage coil with shunt magnet

iii.  Al disc  

iv.  Braking magnet

v.   Registering mechanism.

 

16. How voltage coil is connected in induction type energy meter?

 

Voltage coil is connected in parallel to supply and load in induction type energy meter.

 

17. How current coil is connected in induction type energy meter?

 

Current coil is connected in series to the load in induction type energy meter.

 

18. Why aluminium disc is used in induction type energy meter?

Aluminium disc is used in induction type energy meter because it is a nonmagnetic metal.

 

19. What is the purpose of registering mechanism?

 

The purpose of registering mechanism is to record the energy proportional to the rotations.

 

20. Define creeping.

 

Creeping is defined as slow but continuous rotation of disc when pressure coil is energized and current coil is not energized.

 

21. State the reason why holes are provided in aluminium disc.

Holes are provided on both sides of aluminium disc to avoid creeping.

 


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