Dear Readers, Welcome to Measurement and Instrumentation Interview Questions and Answers have been designed specially to get you acquainted with the nature of questions you may encounter during your Job interview for the subject of Measurement and Instrumentation. These Measurement and Instrumentation Questions are very important for campus placement test and job interviews. As per my experience good interviewers hardly plan to ask any particular questions during your Job interview and these model questions are asked in the online technical test and interview of many IT & Non IT Industries.
Measurement is an act or the result of comparison between the quantity and a predefined standard.
Basic requirements of measurement:-
i.The standard used for comparison purpose must be accurately defined and should be commonly accepted.
ii.The apparatus used and the method adopted must be provable.
Methods for measurement:
* Direct method and
* Indirect method.
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.
Instrument is defined as a device for determining the value or magnitude of a quantity or variable.
Types of instruments:
There are 3 types of instruments
? Mechanical Instruments
? Electrical Instruments and
? Electronic Instruments.
Functions of Instruments:
? Indicating instruments
? Integrating instruments
? Recording instruments
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.
Calibration of instrument:
Th 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.
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.
It is the process by which comparing the instrument with a standard to correct the accuracy.
? Deflecting torque
? Controlling torque
? Damping torque
? PMMC type
? Moving iron type
? Dynamometer type
? Hot wire type
? Electrostatic type
? Induction type
Advantages of PMMC instruments:
? Uniform scale
? No hysterisis loss
? Very accurate
? High effuiciency
Disadvantages of PMMC instruments:
Cannot be used for ac m/s
Some errors are caused by temperature variations.
Applications of PMMC instruments:
? m/s of dc voltage and current
? used in dc galvanometer.
? In ammeter by connecting a shunt resister
? In voltmeter by connecting a series resister.
Advantages of Dynamo meter:
? Can be used for both dc and ac m/s.
? Free from hysteresis and eddy current errors.
? Less expensive
? Can be used for both dc and ac
? Reasonably accurate
? Can be used for both dc and ac
? Unaffected by stray magnetic fields
? Readings are independent of frequency and waveform.
? Fixed coil
? Moving Coil
? Current limiting resister
? Helical spring
? Spindle attached with pointer
? Graduated scale
Td á VI CosÖ
Disadvantages of Dynamo meter:
Readings may be affected by stray magnetic fields.
At low power factor it causes error.
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.
By connecting a capacitor in parallel to the resister.
By using compensating coil.
? Single watt meter method
? Two watt meter method
? Three watt meter method.
? Pressure coil circuit
? Compensation for Pressure coil current
? Compensation for Pressure coil inductance
Method by which energising the pressure coil circuit and current coil circuits separately is called phantom loading.
Power loss is minimized.
? By comparing with std wattmeter.
? By using voltmeter ammeter method.
? By using Potentiometer.
Types of energy meters:
? Electrolytic meters
? Motor meters.
? Clock meters
? Current coil with series magnet
? Voltage coil with shunt magnet
? Al disc
? Braking magnet
? Registering mechanism
It is connected in parallel to supply and load.
It is connected in series to the load.
Why Al disc is used in induction type energy meter.
It gives a valuable number proportional to the rotations.
It provides necessary braking torque.
Creeping: Slow but continuous rotation of disc when pc is energised and cc is not energised.
State the reason why holes are provided in Al disc.
In potentiometer the unknown emf is measured by comparing it with a std known emf.
potentiometer material used
? German silver
? Manganin wire
It is the process by which adjusting the current flows through the potentiometer coil to make the voltage across the std cell is equal.
Applications of Potentiometer:
? Used for m/s of unknown emf
? Used for ammeter calibration
? Used for Voltmeter calibration
? Used for wattmeter calibration
? More accurate
? Easy to adjust
? More complicated
? Accuracy is seriously affected
? Difficulty is experienced in standardization
? Polar potentiometer
? Coordinate potentiometer
It is measured from the position of phase shifter.
? Drysdale Tinsley potentiometer
? Gall Tinsley potentiometer
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.
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