Category: MEASUREMENTS and INSTRUMENTATION Questions

MEASUREMENTS and INSTRUMENTATION Questions and Answers :-

1. A 10MHz CRO has
A. 5MHz sweep
B. 10MHz vertical oscillator
C. 10MHz horizontal oscillator
D. 10MHz supply frequency

ANSWER: C

2. Which of the following instruments can be used to measure AC current only?
A. Permanent Magnet Type ammeter
B. Induction type ammeter
C. Moving iron voltmeter
D. Moving iron ammeter

1. D only
2. B only
3. A, B, D
4. B and D only

ANSWER: 2

3. An oscilloscope indicates
A. Peak to peak value of voltage
B. DC value of voltage
C. RMS value
D. Average value

ANSWER: A

4. In a ballistic galvanometer, the deflecting torque is proportional to
A. the current through coil
B. square of current through coil
C. square-root of current through coil
D. sine of measured

ANSWER: A

5. The error of an instrument is normally given as a percentage of
A. measured value
B. full-scale value
C. mean value
D. rms value

ANSWER: B

6. If the instrument is to have a wide range, the instrument should have
A. Linear scale
B. Square-law scale
C. Exponential scale
D. Logarithmic scale

ANSWER: D

7. The resistance can be measured most accurately by
A. Voltmeter-ammeter method
B. bridge method
C. multimeter
D. Megger

ANSWER: B

8. The repeat accuracy of an instrument can be judged from its
A. static error
B. linearity error
C. dynamic error
D. standard deviation of error

ANSWER: D

9. Which of the following meters has a linear scale?
A. Thermocouple meter
B. Moving iron meter
C. Hot wore meter
D. Moving coil meter

ANSWER: D

10. No eddy current and hysteresis losses occur in
A. Electrostatic instruments
B. PMMC instruments
C. Moving iron instruments
D. Electrodynamo meter instruments

ANSWER: A

11. Two voltmeters have the same range 0-400V. The internal impedance are 30,000 Ohms and 20,000 Ohms. If they are connected in series and 600V be applied across them, the readings are
A. 360V and 240V
B. 300V each
C. 400V and 200V
D. one of the meters out of the range and other 100V

ANSWER: A

12. The full-scale deflection current of an ammeter is 1 mA and its internal resistance is 100Ohm. If this meter is to have full deflection at 5A, what is the value of the shunt resistance to be used?
A. 49.99 Ohms
B. 1/49.99 ohms
C. 1 Ohm
D. 2 Ohms

ANSWER: B

13. The full-scale deflection current of an ammeter is 1 mA and its internal resistance is 100Ohm. This is to have full deflection when 100V is measureD. What is the value of series resistor to be used?
A. 99.99 K ohms
B. 100 K ohms
C. 99.99 ohms
D. 100 ohms

ANSWER: A

14. Why is a MISC meter not recommended for DC measurement?
A. The meter is calibrated for AC and it’s error for DC would be high
B. The meter does not respond to DC signals
C. The error is high due to hysteresis effect
D. The error is high due to eddy current effect

ANSWER: C

15. The EMF of Weston standard cell is measured using
A. Moving- iron meter
B. Moving-coil meter
C. Digital Volt meter
D. Potentiometer

ANSWER: D

16. A mulliammeter can be used as
A. Voltmeter and ammeter
B. Wattmeter
C. Ohmmeter
D. Frequency meter

ANSWER: A

17. Which instrument has identical calibration for ac as well as dc values?
A. Hot wire type
B. Moving coil type
C. Induction type
D. Moving iron type

ANSWER: A

18. An instrument to be used for measurement and control should preferably have
A. Dead zone and dead time
B. Linear output and fast response
C. Non-linear output
D. A highly damped response

ANSWER: B

19. The current coil of a wattmeter is connected to the CT of R-phase. The potential coil is connected across Y and B phases. The wattmeter measures
A. Active power in R phase
B. Active power of Y phase
C. Reactive power of R phase
D. Power proportional to 3 phase power if the load is balanced

ANSWER: C

20. The problem of Electro-static coupling in a transformer is acute at
A. Low frequencies
B. Power frequencies
C. High frequencies
D. High load on the transformer

ANSWER: C

21. Which meter is suitable for the measurement of 10mV at 50MHz?
A. Moving iron voltmeter
B. VTVM
C. Moving coil voltmeter
D. CRO

ANSWER: D

22. It can be stated that
A. CT operates at almost the same flux density as a PT
B. CT operates with a higher flux density than PT
C. CT operates with considerably lower flux density than a PT
D. no generalisation can be made with regard to the flux densities in CT and PT

ANSWER: C

23. The thermocouple instruments do not have
A. High sensitivity
B. Absence of frequency error
C. Independence of ambient temperature
D. High degree of measuring accuracy

ANSWER: D

24. Some wire- wound resistors have bifilar winding. This type of winding is used to
A. Increase the thermal stability
B. Reduce the tolerance
C. Reduce the inductance of winding
D. Double the power rating of the resistor

ANSWER: C

25. Wien bridge is useful for measuring
A. Very high frequency
B. Low frequency
C. Medium frequency
D. High frequency

ANSWER: D

MEASUREMENTS and INSTRUMENTATION Questions and Answers pdf ::

26. A megger is usually
A. Moving iron type instrument
B. Electro-static type instrument
C. Hot-wire type instrument
D. Moving coil type instrument

ANSWER: D

27. A moving iron ammeter may be compensated for frequency errors by
A. a shunt resistance
B. a series inductance
C. shunt capacitance
D. series resistance

ANSWER: C

28. Ryall crest voltmeter is used for measurement of
A. AC voltage of any form
B. Low frequency voltage
C. High DC voltage
D. High AC voltage

ANSWER: D

29. Jewels are used in instruments for the purpose of
A. Damping
B. Torque control
C. Suppressing noise
D. Bearing

ANSWER: D

30. The thermocouple instrument will measure
A. Current
B. Voltage
C. Flux
D. None of the above

ANSWER: D

31. A CRO can display
A. AC signals
B. DC signals
C. Both AC and DC signals
D. Time invariant signals

ANSWER: C

32. The internal resistance of an ammeter should be
A. Very small
B. medium
C. High
D. Infinity

ANSWER: A

33. A galvanometer has
A. air friction damping
B. fluid friction damping
C. Spring coil damping
D. Eddy current damping

ANSWER: D

34. Electrostatic instruments are normally used for
A. Low current measurements
B. High current measurements
C. Low voltage measurements
D. High voltage measurements

ANSWER: D

35. In a moving coil instrument, the deflecting torque is proportional to
A. Current
B. Square of the current
C. Squareroot of the current
D. sine of the measurand

ANSWER: A

36. The absolute measurement of resistance is done by
A. Ohm’s law method
B. Bridge Method
C. Rayleigh method
D. Lorenz method

ANSWER: D

37. To measure the flux, devices used are based on
A. Voltaic effect
B. Piezo-electric effect
C. Hall effect
D. Photo-voltaic effect

ANSWER: C

38. The form factor in AC is the ratio of
A. peak value to average value
B. peak value to rms value
C. rms value to average value
D. rms value to peak value

ANSWER: C

39. PMMC type instruments normally use
A. Air friction damping
B. Fluid friction damping
C. Eddy current damping
D. None of the above

ANSWER: C

40. In a moving iron meter, the deflecting torque is proportional to
A. Current through the coil
B. Square of the current through the coil
C. Sine of the measurand
D. Squareroot of the measurand

ANSWER: B

41. In a gravity controlled instrument, the deflection angle is proportional
A. Measurand
B. Square of the measurand
C. sine inverse of measurand
D. sine of the measurand

ANSWER: C

42. Ampere is one of the
A. Supplementary units
B. Derived units
C. Base units
D. Units used to measure charge

ANSWER: C

43. Direct method is used to measure
A. Length
B. Temperature
C. Pressure
D. Voltage

ANSWER: A

44. A rectifier type instrument is connected to 100VDC and is operated in the DC measuring module reads
A. 111V
B. 90V
C. 50V
D. 100V

ANSWER: A

45. A permanent magnet moving coil ammeter has a coil resistance of 99ohm and Full Scale DeflectionFSD. current of 0.1mA. Shunt resistance is 1 ohm. Current through the meter at 0.5 F.S.D is
A. 0.007mA
B. 0.05mA
C. 0.023mA
D. 0.1mA

ANSWER: B

46. One single phase wattmeter operating on 230V and 5A for 5 hours makes 1940 revolutions. Meter constant in revolutions is 400. What is the power factor of the land?
A. 1
B. 0.84
C. 0.73
D. 0.65

ANSWER: B

47. For power measurement of three phase circuit by two wattmeter method, when the value of power factor is less than 0.5 lagging
A. one of the wattmeters will read zero
B. both give the same readings
C. one of the wattmeter connections will have to be reversed
D. pressure coil of the wattmeter will become ineffective.

ANSWER: C

48. When using ohmmeter, applied voltage is to be disconnected from the circuit because
A. Voltage source will increase resistance
B. Current will decrease resistance
C. the ohmmeter has its own internal battery
D. non of the above

ANSWER: C

49. Which wave has the least form factor?
A. Square wave
B. Rectangular wave
C. Sine wave
D. Triangular wave

ANSWER: A

50. With a sweep time 10ms across the screen the approx. horizontal sawtooth frequency will be
A. 50Hz
B. 100Hz
C. 1kHz
D. 500Hz

ANSWER: B

51. A spring controlled indicating instrument has a deflection of 90deg for maximum current I. The corresponding deflection for a gravity controlled instrument is
A. 90°
B. 120°
C. 30°
D. 0°

ANSWER: C

52. It is found that 10A current passes through a resistor of 10ohms. The resistor has 5% tolerance . The error in measurement of current can be as high as 5%. What is max error in measurement of power, calculated from measured value of I and the nominal value of resistor?
A. 100 W
B. 150W
C.50W
D. 200W

ANSWER: B

53. A resistor of 10Kohms with 5% tolerance is connected in parallel with a 5Kohms resistor of 10% tolerance. What is the tolerance limit for the parallel network?
A. 5%
B. 6.67%
C. 10%
D. 8.33%

ANSWER: D

54. The resistance offered to the passage of an in-varying current by a column of mercury at the temperature of melting ice of mass 14.4521 gms of uniform cross-sectional area and length 106.3cm is
A. Standard ohm
B. One international ohm
C. One ohm according to SI units
D. One ohm according to working standards
ANSWER: B

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MEASUREMENTS and INSTRUMENTATION 2 Mark Questions Answers pdf :-

Unit I Measurement of voltage and Current :-

1. What is meant by measurement?
Measurement is an act or the result of comparison between the quantity and a predefined standard.

2. Mention the basic requirements of measurement.

• The standard used for comparison purpose must be accurately defined and should be commonly accepted.
• The apparatus used and the method adopted must be provable.

3. What are the 2 methods for measurement?

1. Direct method and
2. Indirect method.

4. Explain the function of measurement system.
The measurement system consists of a transducing element which converts the quantity to be measured in an analogous form. the analogous signal is then processed by some intermediate means and is then fed to the end device which presents the results of the measurement.

5. Define Instrument.
Instrument is defined as a device for determining the value or magnitude of a quantity or variable.

6. List the types of instruments.
The 3 types of instruments are

1. Mechanical Instruments
2. Electrical Instruments and
3. Electronic Instruments.

7. Classify instruments based on their functions.

• Indicating instruments
• Integrating instruments
• Recording instruments

8. Give the applications of measurement systems.

• The instruments and measurement systems are sued for
• Monitoring of processes and operations.
• Control of processes and operations.
• Experimental engineering analysis.

9. Why calibration of instrument is important?
The calibration of all instruments is important since it affords the opportunity to
check the instrument against a known standard and subsequently to errors in accuracy.

10. Explain the calibration procedure.
Calibration procedure involves a comparison of the particular instrument with either.

• A primary standard
• A secondary standard with a higher accuracy than the instrument to be calibrated or An instrument of known accuracy.

11. Define Calibration.
It is the process by which comparing the instrument with a standard to correct the accuracy.

12. Name the different essential torques in indicating instruments.

• Deflecting torque
• Controlling torque
• Damping torque

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

• PMMC type
• Moving iron type
• Dynamometer type
• Hot wire type
• Electrostatic type
• Induction type.

14. State the advantages of PMMC instruments

• Uniform scale.
• No hysterisis loss
• Very accurate
• High effuiciency.

15. State the disadvantages of PMMC instruments

• Cannot be used for ac m/s
• Some errors are caused by temperature variations.

16. State the applications of PMMC instruments

m/s of dc voltage and current used in dc galvanometer.

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

• In ammeter by connecting a shunt resister
• In voltmeter by connecting a series resister.

18. State the advantages of Dynamometer type instruments

• Can be used for both dc and ac m/s.
• Free from hysterisis and eddy current errors.

19. State the advantages of Moving iron type instruments

• Less expensive
• Can be used for both dc and ac
• Reasonably accurate.

20. State the advantages of Hot wire type instruments

• Can be used for both dc and ac
• Unaffected by stray magnetic fields
• Readings are independent of frequency and waveform.

Unit II Measurement of Power and Energy :-

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

• Fixed coil
• Moving Coil
• Current limiting resister
• Helical spring
• Spindle attached with pointer
• Graduated scale

2. Write down the deflecting torque equation in dynamometer type wattmeter.
Td  VI Cos

3. State the disadvantages of Dynamometer type wattmeter.

• Readings may be affected by stray magnetic fields.
• At low power factor it causes error.

4. Name the errors caused in Dynamometer type wattmeter.

• Error due to pressure coil inductance
• Error due to pressure coil capacitance
• Error due to methods of connection
• Error due to stray magnetic fields
• Error due to eddy current.

5. How the errors caused by pc inductance is compensated.
By connecting a capacitor in parallel to the resister.

6. How the errors caused by methods of connection is compensated
By using compensating coil.

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

1. Single wattmeter method
2. Two wattmeter method
3. Three wattmeter method.

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

• Pressure coil circuit
• Compensation for Pressure coil current
• Compensation for Pressure coil inductance.

9. Define Phantom loading.
Method by which energizing the pressure coil circuit and current coil circuits
separately is called phantom loading.

10. State the use of phantom loading.
Power loss is minimized.

11. Name the methods used in Wattmeter calibration.

• By comparing with std wattmeter.
• By using voltmeter ammeter method.
• By using Potentiometer.

12. What are the types of energy meters?

• Electrolytic meters
• Motor meters.
• Clock meters

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

• Current coil with series magnet
• Voltage coil with shunt magnet
• Al disc
• Braking magnet
• Registering mechanism.

14. How voltage coil is connected in induction type energy meter.
It is connected in parallel to supply and load.

15. How current coil is connected in induction type energy meter.
It is connected in series to the load.

16. Why Al disc is used in induction type energy meter.
Aluminum is a nonmagnetic metal.

17. What is the purpose of registering mechanism.
It gives a valuable number proportional to the rotations.

18. What is the purpose of braking mechanism.
It provides necessary braking torque.

19. Define creeping.
Slow but continuous rotation of disc when pc is energized and cc is not energized.

20. State the reason why holes are provided in Al disc.
To avoid creeping holes are provided on both sides of Al disc.

Unit III Potentiometer and Instrument Transformers :-

1. What is the basic principle used in potentiometer.
In potentiometer the unknown emf is measured by comparing it with a std known emf.

2. Name the potentiometer material used.
German silver
Manganin wire

3. Define standardization.
It is the process by which adjusting the current flows through the potentiometer coil to make the voltage across the std cell is equal.

4. State the applications of potentiometer.

• Used for m/s of unknown emf
• Used for ammeter calibration
• Used for Voltmeter calibration
• Used for wattmeter calibration

5. State the advantages of crompton potentiometer.

• More accurate
• Easy to adjust

6. What are the practical difficulties in ac potentiometers.

• More complicated
• Accuracy is seriously affected
• Difficulty is experienced in standardization.

7. Classify ac potentiometers.

• Polar potentiometer
• Coordinate potentiometer.

8. How the phase angle is measured in polar type potentiometers.
It is measured from the position of phase shifter.

9. Name some ac potentiometers.

• Drysdale Tinsley potentiometer
• Gall Tinsley potentiometer

10. State the advantages of ac potentiometers.

• Can be used for m/s of both magnitude and phase angle
• Can be used for m/s of inductance of the coil.
• It is used in m/s of errors in CTS

11. State the applications of ac potentiometers.

• M/s of self inductance.
• Ammeter calibration
• Voltmeter calibration
• Wattmeter calibration.

12. State the advantages of instrument transformers.

• Used for extension of range
• Power loss is minimum
• High voltage and currents can be measured.

13. State the disadvantage of instrument transformers.
Cannot be used for dc measurements.

14. What are the constructional parts of current transformer?
Primary winding
Secondary winding
Magnetic core.

15. Name the errors caused in current transformer.
Ratio error
Phase angle error

16. Define ratio error.
The ratio of energy component current and secondary current is known as the ratio error.

17. How the phase angle error is created.
It is mainly due to magnetizing component of excitation current.

18. State the use of potential transformer.
Used for m/s of high voltage
Used for energizing relays and protective circuits.

19. Name the errors caused in potential transformer.
Ratio error
Phase angle error.

20. How the CT and PT are connected in the circuits.
CT is connected in series and PT is connected in parallel.

Unit IV Resistance Measurement :-

1. Classify resistance.
Low resistance
Medium resistance
High resistance

2. What is the range of medium resistance?
Resistance of about 1 ohm to 100 kilo ohms are called medium resistance.

3. Name the methods used for low resistance measurement.
Ammeter – voltmeter method
Potentiometer method
Kelvin double bridge method
Ohm meter method.

4. Name the methods used for medium resistance measurement
Ammeter – voltmeter method
Substitution method
Wheatstone bridge method
Carey foster bridge method.

5. Where high resistance m/s is required?
Insulation resistance of cables
High resistance circuit elements
Volume resistivity of a material
Surface resistivity.

6. State the advantages of Wheatstone bridge method.
Free from errors
The balance is quit independent of source emf

7. State the advantages of Kelvin double bridge method.
Errors owing to contact resistance, resistance of leads can be eliminated by using
this Kelvin double bridge.

8. What are the constructional features of doctor ohmmeter?
Permanent magnet
Current coil
Pressure coil
Battery
Pointer with graduated scale.

9. Define megger.
The megger is an instrument used for the measurement of high resistance and
insulation resistance.

10. Name the parts of megger.
It consists of a hand driven dc generator and a direct reading true ohm meter.

11. What is the range of low resistance?
Resistance of about 1 ohm and under are included in this class.

12. What is the range of medium resistance?
Resistance of 100 kilo ohms and above are usually termed as high resistance.

13. What ranges of resistance can be measured by using doctor ohmmeter.
0 to 500 micro ohms
0 to 5 milli ohms
0 to 50 milli ohms
0 to 500 milli ohms
0 to 5 ohms.

14. How resistance is measured in direct deflection method.
The deflection of galvanometer connected in series with the resistance to be
measured gives a measure of the insulation resistance.

15. Classify the cables according to their sheathing.
Armoured cables
Unarmoured cables.

16. Name the leads present in megger.
Earth lead
Line lead
Guard lead.

17. How resistance is measured by using ohm meter method.
Series ohm meter method
Shunt ohm meter method.

18. How resistance is measured in loss of charge method.
In this method a capacitor is charged and discharged for a specific time period and from this resistance is measured.

19. State the balance equation used in bridge methods.
The product of opposite branch resistances are equal.

20. State the advantages of price’s guard wire method.
In this method leakage current does not flows through the meter and therefore it gives accurate reading.

21. How the earth resistance is measured.
By using earth megger the value of surface earth resistance can be measured.

Unit V Impedance Measurement :-

1. State the use of ac bridges.
AC bridges are used for the m/s of self and mutual inductance and capacitance.

2. State the balance equation used in ac bridges.
The product of opposite branch impedances are equal.

3. Name the bridge circuits used for the m/s of self inductance.
Maxwell’s bridge
Maxwell-Wein Bridge
Anderson bridge
Hay’s bridge.

4. Name the bridge circuits used for the m/s of capacitance.
De Sauty’s bridge
Schering Bridge
Wein bridge

5. Name the bridge circuits used for the m/s of mutual inductance.
The Heaviside Campbell bridge
The Campbell bridge.

6. Which type of detector is used in ac bridges?
Vibration galvanometers are used.

7. Name the ac sources used in ac bridges.
AC supply with step-down transformer
Motor driven alternator
Audio frequency and radio frequency oscillator.

8. In which cases audio frequency oscillators are used as ac source.
For high frequency ac requirement audio frequency oscillators are used.

9. Name the sources of errors in ac bridge m/s.
Errors due to stray magnetic fields
Leakage errors
Eddy current errors
Residual errors
Frequency and waveform errors.

10. State the advantages of Maxwell-wein bridge.
The balance equation is independent of frequency and therefore more accurate.

11. State the disadvantage of Maxwell-wein bridge.
This method needs a std variable capacitor. Variable Capacitor is costliest.

12. State the disadvantages of Hay’s bridge.
The balance equation is dependent of frequency and therefore any changes in frequency will affect the m/s.

13. State the use of Wein bridge.
It is used for the m/s of unknown capacitance and frequency.

14. What is the use of Campbell bridge?
This is used for the m/s of mutual inductance.

15. What is meant by inductometer?
The std variable mutual inductance meter is called as inductometer.

16. Define Q-factor of the coil.
It is the ratio between power stored in the coil to the power dissipated in the coil.

17. Name the components of iron loss.
Eddy current loss
Hysterisis loss.

18. Name the faults that occurs in cables.

• Break down of cable insulation
• Short circuit fault
• Open conductor fault.

19. Name the loop test methods used in location of fault.

• Murray loop test
• Varley loop test.

20. How leakage errors are minimized in ac bridge circuits.
By using high grade insulation.

MEASUREMENTS and INSTRUMENTATION 2 Mark Questions Answers :-