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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