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Measurements and Instrumentation (EE2201)
UNIT I
INTRODUCTION
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?
Direct method and
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
Mechanical Instruments
Electrical Instruments and
Electronic Instruments.
7. Classify instruments.
Absolute Instruments
Secondary Instruments
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8. What are the 2 modes of operation of secondary Instruments?
Analog mode and
Digital mode
9. What are analog devices?
Signals that vary in a continuous fashion and take on an infinity of values in
any range are called analog signals. The devices that produces these signals are
called analog devices
10. What are digital devices?
Signals that vary in discrete steps and thus take on only finite differentvalues in a given range are called digital signals. The devices that produces these
signals are called digital devices.
11. Mention the functions performed by the measurement system.
Indicating function
Recording function
Controlling function.
12.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.
13. List the functional elements of the measurement systems.
Primary sensing element.
Variable conversion element and Data processing element.
14. What is signal conditioning?
The performing of non-linear processes like modulation, detection,
sampling, filtering, chopping and clipping etc. on the signal to bring it to desired
form is called signal conditioning.
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15. What is data transmission element?
When the elements of an instrument are actually physically separated, it
becomes necessary to transmit data from one to another. The element thatperforms this function is called a data transmission element.
16. Give the function of the variable manipulation element.
The function of the variable manipulation element is to manipulate the
signal presented to it preserving the original nature of the signal.
17. What are the characteristics of the measurement system?
Static characteristics
Dynamic characteristics
18. 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.
19. 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.
20.What are the static characteristics? (AU April 2004)
Accuracy Sensitivity
Reproducibility
Drift
Static error and
Dead zone.
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21.Define true value
True value of a quantity to be measured is defined as the average of aninfinite number of measured values when the average deviation to the various
contributing factors tends to zero.
22.Define scale range.
The scale range of an instrument is defined as the difference between the
largest and smallest reading of the instrument.
23. What is meant by reproducibility?.(AU Nov 2004)
Reproducibility is the degree of closeness with which a given value may be
repeatedly measured. It may be specified in turns of units for a given period of
time.
24. Define repeatability.(AU Nov 2004)
Repeatability is defined as the variation of scale reading and is random in
nature.
25.Define noise.
Noise is defined as any signal that does not convey any useful information.
26. What is accuracy?(AU may 2005)
Accuracy is the closeness with which an instrument reading approaches the
true value of the quantity being measured.
27.What is precision?
Precision is measure of the reproducibility of the measurements, i.e. given afixed value of a quantity; it is a measure of the degree of agreement within a group
of measurements.
28. Mention the characteristics of precision.
Conformity and
Number of significant figures.
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29.What are the different types of errors?(AU Nov 2004)
*Gross error
* Systematic error
* Random error
30.Define Fidelity.
Fidelity of a system is defined as the ability of a system to reproduce the same
output in the same form as the input.
31. What is Dynamic error?
Dynamic error is difference between the true value of the quantity changing with
the time and the value indicated by the instrument if no static error is assumed.
32.Define relative limiting error.
Relative limiting error is defined as the ratio of the error to the specified to the
magnitude of the quantity.
33.Define static error.(AU Nov 2004)
Static error is defined as the difference between the measured value and true value
of the quantity.
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UNIT IIELECTRICAL & ELECTRONICS INSTRUMENTS
1. Mention the two main differences between a flux meter and a BallisticGalvanometer.
Flux meter Ballistic
Galvanometer
Controlling torque is very small controlling torque is high
Heavy electromagnetic damping electromagnetic damping is not heavy
Less sensitive more sensitive
Less accurate more accurate
2. What are the adjustments in energy meter?
Main speed adjustment
Power factor adjustment
Friction adjustment
Creep adjustment
3. Write about DC tests in magnetic measurements.
These are used to determine B-H curve and hysteresis loop of Ferro-
magnetic materials. The direct current is used to have variable m.m.f. and
flux meter is used to measure the flux density. A ballistic galvanometer can
be used to measure flux density. Such tests are also called ballistic tests.4. Give two differences between analog and digital type phase meters.
Analog type Digital Type
This is called balanced modulator method this is called flip-flop method
Accuracy is very less high as 0.1o
can be achived
Less stable, sensitive & reliable high stable, sensitive and reliable
DC meter is used at the output display unit is used at the output
5. What is creeping?
Without any current through current coil, disc rotates due to the
supply voltage exciting its pressure coil. This is called creeping.
6. Write some advantages of instrument transformer.
The normal range ammeters and voltmeters can be used along with
these transformers to measure high currents and voltage.
The rating of low range meter can be fixed irrespective of the value of
high voltage or current to be measured
These transformers isolate the measurement from high voltage and
current circuits. This ensures safety of the operator and makes the
handling of the equipments very easy and safe.
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These can be used for operating many types of protecting devices such
as relays or pilot lights.
7. Define the terms digitizing and digitizing period.
In the digital voltmeters, it is necessary to convert the analog signal to
digital signal. Various techniques used to achieve this conversion. The circuits
which are used to achieve such conversion are called digitizing circuits and
the process is called digitizing. The time required for this conversion is called
digitizing period.
8. What are the requirements of a shunt?
The temperature coefficient of shunt and the meter should be low and
should be as equal as possible.
The shunt resistance should be stable and constant with time.
The shunt resistance should not carry currents which will cause excessive
temperature rise.
The soldering joints should not cause a voltage drop.
The values of resistance should not change due to soldering.
The resistance should have low thermal electromotive force with copper.
9. Mention any two precautions to be taken while using a voltmeter.
It should be always connected across the circuit or component whose
voltage is to be measured.
The polarities must be observed correctly.
First use the highest range and then decrease the voltage range until the
sufficient deflection is obtained.
Take care of loading effect.
10. Mention the two main differences between an ammeter and a
voltmeter.
Ammeter Voltmeter
It is a current measuring device it is a voltage measuring deveice
Always connected in series with circuit Always connected in parallel with circuit
The resistance is very small The resistance is very high
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11. What are the adjustments in energy meter?
Main speed adjustment Power factor adjustment
Friction adjustment
Creep adjustment
12. Write about AC tests in magnetic measurements.
When a ferro-magnetic material is subjected to cycle of magnetization
and demagnetization then the eddy current and hystereis losses occur. Hence
alternating current is used to determine iron losses, having provision of a
variable frequency and form factor. Such tests are carried out at power, audio
or radio frequencies.
13. Mention the errors in Moving iron instruments.
Hysteresis error
Temperature error
Stray magnetic field error
Frequency error
Eddy current error
14. How can we prevent creeping in energy meter?
Two holes are drilled in the aluminum disc 180o
opposite to each other.
When this holes comes under the shunt magnet pole, it gets acted upon by a
torque opposite to the rotation.
15. Mention the purpose of Schmitt trigger in frequency meter.
To convert the amplified signal from sine wave to square wave with fast
rise and fall times.
16.Define torque to weight ratio in electrodynamometer instrument.
To have reasonable deflecting torque, mmf of the MC must be enough.
Thus mmf=NI, hence current through MC should be high or no. Of turns
should be large. The current cannot be made high because it may cause
excessive heating of spring. Large no. of N hence is the only option but it
increases weight of the coil.
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17.What are the requirements of a Multiplier?
Their resistance should not change with time
The change in their resistance with temperature should be small. They should be non-inductively wound for a.c. meters.
18.Mention any two precautions to be taken while using an Ammeter.
It should never be connected across any source.
The polarity must be observed correctly.
First use the highest range and then decrease the voltage range until the
sufficient deflection is obtained.
19.What are instrument transformer?
Transformers used in conjunction with measuring instrument for measuring
purposes are called instrument transformers. The transformers used for
measurement of current is called current transformers. The transformers used for
measurement of voltage are called potential transformers.
20.What are the different types of frequency meters?
The different types of frequency meters are:
1.Mechanical resonant type2.Electrical resonance type
3.Electrodynamometer type
4.Weston type
5.Ratiometer type
6.Saturable core type
21.What are the different types of electrical resonance type frequency
meters?
The two types of electrical resonance type frequency meters are :1. Ferrodynamic type frequency meter
2. Electrodynamometer type frequency meter.
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UNIT III
COMPARISON METHODS OF MEASUREMENTS
1. Define D.C potentiometer
A potentiometer is an instrument designed to measure an
unknown voltage by comparing it with a unknown voltage.
2.List the application of D.C potentiometer.
Measurement of Voltage
Calibration of Voltmeter
Calibration of Ammeter Calibration of Wattmeter
3.What is A.C potentiometer?
A.C potentiometer is user for measurement of alternating voltages
and currents.
4.Give the purpose of bridge circuits. What are the different type?
The bridge circuits are used in instrumentation systems for the
measurement of resistance , inductance and capacitance.
Types:
DC type and
AC type.
5.What are the 2 types of wheatstone bridge?
Null type bridge
Deflection type bridge.
6.What are the different types of AC bridges?
Maxwells Inductance bridge
Maxwells inductance-Capacitance bridge
Hays bridge
Andersons bridge
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Owens Bridge
High voltage Schering
7. Define slew rate
Slew rate is defined as the maximum output voltage change per unit time.
8. What is the basic principle used in potentiometer.
In potentiometer the unknown emf is measured by comparing it with a std
known emf.
Name the potentiometer material used.
German silver
Manganin wire
9. 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.
10. State the applications of potentiometer.
Used for m/s of unknown emf
Used for ammeter calibration
Used for Voltmeter calibration
Used for wattmeter calibration
11. State the advantages of crompton potentiometer.
More accurate
Easy to adjust
12. 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.
13. How the phase angle is measured in polar type potentiometers.
It is measured from the position of phase shifter.
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14. Name some ac potentiometers.
Drysdale Tinsley potentiometer
Gall Tinsley potentiometer
15. 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
16. State the applications of ac potentiometers.
M/s of self inductance.
Ammeter calibration
Voltmeter calibration
Wattmeter calibration.
17. State the advantages of instrument transformers.
Used for extension of range
Power loss is minimum
High voltage and currents can be measured.
18. State the disadvantage of instrument transformers.
Cannot be used for dc measurements.
19. What are the constructional parts of current transformer?
Primary winding
Secondary winding
Magnetic core.
20. Name the errors caused in current transformer.
Ratio error
Phase angle error
21. Define ratio error.
The ratio of energy component current and secondary current is known as the
ratio error.
22. How the phase angle error is created.
It is mainly due to magnetizing component of excitation current.
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23. State the use of potential transformer.
Used for m/s of high voltage
Used for energizing relays and protective circuits.
24. Name the errors caused in potential transformer.
Ratio error
Phase angle error.
25. How the CT and PT are connected in the circuits.
CT is connected in series and PT is connected in parallel.
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UNIT- IV
STORAGE AND DISPLAY DEVICES
1. List the components of a magnetic tape recorder.( AU Nov 2005)
Magnetic tape
Reproducing head
Tape transport mechanism
Conditioning devices.
Recording head
2. Mention the different methods of magnetic tape recording.(AU May 2005)
Direct recording
Frequency modulation (FM) recording and
Pulse duration modulation (PM) recording.
3. What is the purpose of erase head?
In the erase head, a signal of high frequency and level sweeps the magnetic
tape thereby completely wiping out the information contained there in. this renders
the magnetic tape to be used fresh for smother signal.
4. What is drop out?
In direct recording, some portions of the tape may not be perfectly recorded
owing to dirt or poor manufacturer and this is called drop out.
5. Mention the 2 factors in FM recording
Percentage deviation and
Deviation ratio
6. What is the operation of a serial printer?
The serial printer produces a single character at a time, usually moving
from left to right across a page. It prints 200 characters per second.
7. Mention the purpose of line printers.
The line printers are used to print and entire line simultaneously. It points
4000 lines per minute.
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8. Give the operation of pare printers.
The page printer prints in a line at a time mode, but can be stopped and
restarted only on the page basis. The top speed is 45,000 lines per minute.
9. List the classification of printers.
Impact and non-impact printers.
Fully formed character and dot matrix character printer.
Character at a time and a line at a time.
10. What is daisy wheel printer?
Daisy wheel printer is a fully formed character printer, designed forcomputer usage and has characters mounted on the periphery of a spinning print
head similar to a daisy flow. They are capable of bi-directional printing.
11. Give short notes on dot-matrix printers.
In dot-matrix printers, the characters are formed by printing a group of dots
to form a letter, no. or other symbols. It can print any combination of dots with all
available print position in the matrix.
12. List the important features of CRTs.
Size
Phosphor
Operating voltages
Deflection voltages
Viewing screen .
13. What is meant by deflection sensitivity in CRT?(AU may 2005)
The deflection sensitivity of the CRT is usually stated as the DC voltagerequired for each cm of deflection of the spot on the screen.
14. What is meant by recurrent sweep in CRT?
When the saw tooth, being an AC voltage alternates rapidly, the display
occurs respectively, so that a lasting image is seen by the eye. This repeated
operation is known as recurrent sweep.
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UNIT V
TRANSDUCERS AND DATA ACQUISITION SYSTEMS
1. Define transducers.
Transducers are defined as a device which when actuated, transforms
energy from one form to another. Generally, any physical parameters is
converted into electrical form.
2. What are the 2 types of transducers?
Electrical and
Mechanical
3. Name the parameters that dictate the transducer capability
Linearity
Repeatability
Resolution and
Reliability
4. Define sensitivity
Sensitivity is defines as the electrical output per unit change in the
physical parameter. High sensitivity is generally desirable for a transducer.
5. Classify electrical transducers.
Active
Passive
6. Name the 2 parts of a transducer
Sensing element
Transduction element
7. Mention the factors considered while selecting a transducer.
Operating range
Sensitivity
Frequency response & resonant frequency
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13.Write notes on LVDT
It is the linear variable differential transformer which is used to translatethe linear motion into electrical signals. It consists of a single primary
winding and 2 secondary winding.
14. List the advantages of LVDT
High range of displacement measurement
Friction & electrical isolation
Immunity from external effects
High I/p and high sensitivity
Ruggedness
Low hysterisis & low power consumption.
15.What is a digitizer?
It is a digital encoding transducer that enables a linear or rotary
displacement to be directly converted into digital form without intermediate
forms of analog to digital (A/D) conversion.
16.What are the disadvantages of LVDT?
The disadvantages of LVDT are:
1.Relatively large displacements are required for appreciable
differential input.
2. The transducer performance is affected by vibrations.
3.The receiving instrument can be selected to operated on ac
signals or a demodulator network must be used if a D.C output is required.
17.Write down the principle of operation of capacitive transducers.
The principle of operation of capacitive transducers are given as,
Where , A=Overlapping area of plates in m2
d= distance between two plates in m.
r= relative permittivity
o= Permittivity of free space(8.85*10-12
F/m)
18.List out the advantages of capacitive transducer.
The advantages of capacitive transducer are
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1.They require extremely small forces to operate
2.They are extremely sensitive
3.They have a high input impedance and hence minimum loading effects
4.They have a good frequency response and require small power tooperate them.
20.What is the disadvantage of piezo electric transducer?
The disadvantage of piezo electric transducer is that it cannot measure
static conditions.The output voltage is affected by the temperature variation of
the crystal.
21.What is digital transducers?
Digital transducers are called as encoders. They are normally in the form
of linear or rotary displacement transducers .Hence they require digital to
analog converter to realize the digital data.
22.What is meant by Data acquisition?
Data acquisition relates to the process of collecting the input data in
digital form as rapidly, accurately and economically as necessary.
23. List the instruments that are needed for data acquisition system.
*DPM with digital outputs
* a shaft digitizer
*sophisticated high speed resolution device
24.List the basic components of D/A converter.
*flip flop register
* DAC modules
25.List the methods used for analog to digital conversion.
The methods used for analog to digital conversion are
1.Successive approximation type
2.Voltage to time conversion method
3.Voltage to frequency conversion method
4.Dual slope integration method