Classification of Transducers Questions and Answers

Q: The best suited flow-meter to handle corrosive liquids is :

The best flow-meter for corrosive liquids is the magnetic flow-meter.An electromagnetic flow-meter measures the voltage induced in a conducting liquid flowing through a magnetic field (Faraday's law). It has no moving parts and nothing obstructing the flow, and its tube can be lined with corrosion-resistant materials such as PTFE, so corrosive and dirty liquids do not damage it.Displacement, piston type and turbine meters all have moving parts in contact with the liquid, which corrosive fluids would wear and attack.

Q: Match the pairs :Set ISet II(a) Piezo-electric(i) Temperature measurement(b) Foil strain gauge(ii) Displacement measurement(c) Beta gauge(iii) Pressure measurement(d) LVDT(iv) Thickness measurement

The answer is (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii), as the key gives. Three pairs are firm and the fourth is forced.A piezo-electric element converts pressure or force to charge, so (a) goes with pressure. A beta gauge measures thickness from how far a sheet absorbs beta radiation, so (c) goes with thickness. An LVDT (linear variable differential transformer) measures displacement, so (d) goes with displacement.That leaves temperature for the foil strain gauge. A strain gauge normally measures strain, and through it force or pressure, and temperature enters only as an error to be compensated, so the pairing is the paper's forced match rather than a natural one. No other option can be consistent with the three firm pairs: option A makes the piezo-electric element a thickness sensor, option B makes the beta gauge a temperature sensor, and option D pairs every item wrongly.

Q: Which of the following is highly sensitive transducer ?

The key names the thermistor as the highly sensitive transducer.The passage defines sensitivity as the ratio of the change in output to the change in input. A thermistor's resistance changes by several percent for each degree Celsius (about -4 % per degree for a typical NTC type), which is far more than a thermocouple, whose output changes by only some tens of microvolts per degree. A potentiometer is a position transducer with a change per unit of travel set by its supply, and its output is not small-signal sensitive in the same way.A photodiode is also very sensitive to light, which is why this item is a best-answer one; the key reads the question as being about temperature-type transducers, where the thermistor is the highly sensitive choice.

Q: The one of the disadvantages of magnetic flowmeters is :

The disadvantage is that it handles only fluids having adequate electrical conductivity.A magnetic flowmeter works by Faraday's law: a conducting fluid moving through a magnetic field induces a voltage proportional to its velocity, picked up by electrodes. If the fluid is not conductive enough, as with oils, hydrocarbons and pure water, no usable voltage is produced, so the meter cannot be used. The paper's wording is 'adequate electrical conductors'.Handling slurries, greasy material and corrosive fluids, and causing very low pressure drop because there is no obstruction in the pipe, are advantages of magnetic flowmeters, not disadvantages.

Q: One of the following transducers is very popular for measurement of rotational displacements :

The transducer popular for rotational displacement is the shaft encoder.A shaft encoder, optical or magnetic, is mounted on a rotating shaft and gives digital pulses or a digital code as it turns. Incremental encoders count pulses to measure angle and speed; absolute encoders give a unique code for each angular position. They are widely used in motors, robots and CNC machines.An LVDT (linear variable differential transformer) measures linear displacement; its rotary counterpart is the RVDT. Strain gauges measure strain, and differential capacitors are used mainly for small linear displacements. None of these is the standard choice for rotation.

Q: What is the name of a device that converts sound waves to electrical waves ?

The device is a microphone.A microphone is a transducer that converts the pressure variations of sound waves into a corresponding electrical signal. In a dynamic microphone a diaphragm moves a coil in a magnetic field; in a condenser microphone the diaphragm changes the capacitance of a charged capacitor; piezoelectric and MEMS types are also common.An amplifier increases the strength of an electrical signal but does not convert sound. A recorder stores signals. A filter passes some frequencies and blocks others. None of them is the sound-to-electrical converter.

The best suited flow-meter to handle corrosive liquids is :

A.Displacement flow-meter
B.Piston type flow-meter
C.Turbine flow-meter
D.Magnetic flow-meter

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

Answer: D

The best flow-meter for corrosive liquids is the magnetic flow-meter.

An electromagnetic flow-meter measures the voltage induced in a conducting liquid flowing through a magnetic field (Faraday's law). It has no moving parts and nothing obstructing the flow, and its tube can be lined with corrosion-resistant materials such as PTFE, so corrosive and dirty liquids do not damage it.

Displacement, piston type and turbine meters all have moving parts in contact with the liquid, which corrosive fluids would wear and attack.

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Match the pairs :

Set I	Set II
(a) Piezo-electric	(i) Temperature measurement
(b) Foil strain gauge	(ii) Displacement measurement
(c) Beta gauge	(iii) Pressure measurement
(d) LVDT	(iv) Thickness measurement

A.(a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
B.(a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
C.(a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)
D.(a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: C

The answer is (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii), as the key gives. Three pairs are firm and the fourth is forced.

A piezo-electric element converts pressure or force to charge, so (a) goes with pressure. A beta gauge measures thickness from how far a sheet absorbs beta radiation, so (c) goes with thickness. An LVDT (linear variable differential transformer) measures displacement, so (d) goes with displacement.

That leaves temperature for the foil strain gauge. A strain gauge normally measures strain, and through it force or pressure, and temperature enters only as an error to be compensated, so the pairing is the paper's forced match rather than a natural one. No other option can be consistent with the three firm pairs: option A makes the piezo-electric element a thickness sensor, option B makes the beta gauge a temperature sensor, and option D pairs every item wrongly.

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Direction for [ Question No: 3 To 3 ] :

The static characteristics of an instrument are, in general, considered for instruments which are used to measure an unvarying process condition. All the static performance characteristics are obtained by one form or another of a process called calibration. There are a number of related definitions (or characteristics), which are described below, such as accuracy, precision, repeatability, resolution errors, sensitivity, etc.
(1) Instrument : A device or mechanism used to determine the present value of the quantity under measurement.
(2) Measurement : The process of determining the amount, degree, or capacity by comparison (direct or indirect) with the accepted standards of the system units being used.
(3) Accuracy : The degree of exactness (closeness) of a measurement compared to the expected (desired) value.
(4) Resolution : The smallest change in a measured variable to which an instrument will respond.
(5) Precision : A measure of the consistency or repeatability of measurements i.e., successive reading do not differ. (Precision is the consistency of the instrument output for a given value of input).
(6) Expected value : The design value i.e., the most probable value that calculations indicate one should expect to measure.
(7) Error : The deviation of the true value from the desired value.
(8) Sensitivity : The ratio of the change in output (response) of the instrument to a change of input or measured variable.

Which of the following is highly sensitive transducer ?

A.Photodiode
B.Potentiometer
C.Thermocouple
D.Thermistor

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: D

The key names the thermistor as the highly sensitive transducer.

The passage defines sensitivity as the ratio of the change in output to the change in input. A thermistor's resistance changes by several percent for each degree Celsius (about -4 % per degree for a typical NTC type), which is far more than a thermocouple, whose output changes by only some tens of microvolts per degree. A potentiometer is a position transducer with a change per unit of travel set by its supply, and its output is not small-signal sensitive in the same way.

A photodiode is also very sensitive to light, which is why this item is a best-answer one; the key reads the question as being about temperature-type transducers, where the thermistor is the highly sensitive choice.

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The one of the disadvantages of magnetic flowmeters is :

A.Handle slurries and greasy material only
B.Handles corrosive fluids
C.Very low pressure drop
D.Handles fluids having adequate electrical conductors

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: D

The disadvantage is that it handles only fluids having adequate electrical conductivity.

A magnetic flowmeter works by Faraday's law: a conducting fluid moving through a magnetic field induces a voltage proportional to its velocity, picked up by electrodes. If the fluid is not conductive enough, as with oils, hydrocarbons and pure water, no usable voltage is produced, so the meter cannot be used. The paper's wording is 'adequate electrical conductors'.

Handling slurries, greasy material and corrosive fluids, and causing very low pressure drop because there is no obstruction in the pipe, are advantages of magnetic flowmeters, not disadvantages.

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One of the following transducers is very popular for measurement of rotational displacements :

A.Shaft encoder
B.Differential capacitor
C.LVDT
D.Strain gauge

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: A

The transducer popular for rotational displacement is the shaft encoder.

A shaft encoder, optical or magnetic, is mounted on a rotating shaft and gives digital pulses or a digital code as it turns. Incremental encoders count pulses to measure angle and speed; absolute encoders give a unique code for each angular position. They are widely used in motors, robots and CNC machines.

An LVDT (linear variable differential transformer) measures linear displacement; its rotary counterpart is the RVDT. Strain gauges measure strain, and differential capacitors are used mainly for small linear displacements. None of these is the standard choice for rotation.

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What is the name of a device that converts sound waves to electrical waves ?

A.an amplifier
B.a recorder
C.a filter
D.a microphone

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: D

The device is a microphone.

A microphone is a transducer that converts the pressure variations of sound waves into a corresponding electrical signal. In a dynamic microphone a diaphragm moves a coil in a magnetic field; in a condenser microphone the diaphragm changes the capacitance of a charged capacitor; piezoelectric and MEMS types are also common.

An amplifier increases the strength of an electrical signal but does not convert sound. A recorder stores signals. A filter passes some frequencies and blocks others. None of them is the sound-to-electrical converter.

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List - I	List - II
(a) LVDT	(i) Pressure
(b) Bourdon tube	(ii) Temperature
(c) Strain gauge	(iii) Displacement
(d) Thermistor	(iv) Stress

Codes :
(a) (b) (c) (d)

A.(iv) (iii) (ii) (i)
B.(iii) (ii) (i) (iv)
C.(iv) (i) (iii) (ii)
D.(iii) (i) (iv) (ii)

Exam Year(s)

UGC NET - 2012,

Answer: D

An LVDT measures displacement (iii), a Bourdon tube measures pressure (i), a strain gauge measures stress (iv) through the strain in the material, and a thermistor measures temperature (ii). The code is (iii) (i) (iv) (ii), option D. Options A and C give the LVDT stress or pressure, and option B pairs the LVDT with temperature, which a thermistor measures, so all three fail the first pair.

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Direction for [ Question No: 8 To 8 ] :

Directions : In the following questions, match List - I and List - II and select the correct answer using the codes given below the lists :

List - I	List - II
a. Strain measurement	i. Pt-100
b. temperature measurement	ii. load cell
c. Lissajous figures	iii. bio-medical signals
d. E.M.G.	iv. C.R.O.

Codes : a b c d

A.i ii iv iii
B.ii i iv iii
C.iii ii i iv
D.iii iv ii i

Exam Year(s)

UGC NET - 2012,

Answer: B

The matching is: a strain measurement with load cell (ii), b temperature measurement with Pt-100 (i), c Lissajous figures with C.R.O. (iv), d E.M.G. with bio-medical signals (iii), the code ii i iv iii (option B).

A load cell is a strain-gauge transducer, a Pt-100 is a platinum resistance thermometer, Lissajous figures are shown on a cathode ray oscilloscope, and the electromyogram is a bio-medical signal. Options A, C and D swap the load cell and the Pt-100 or give the E.M.G. to another item.

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The hygrometer is an instrument used to measure

1. rainfall 2. altitude
3. relative humidity 4. temperature Which of the following is true ?

A.1 and 2 is true.
B.1 and 4 is true.
C.3 is true.
D.3 and 4 is true

Exam Year(s)

UGC NET - 2013,

Answer: C

Only statement 3 is true, which is option (C). A hygrometer measures relative humidity, the amount of water vapour in the air compared with the most it could hold at that temperature. Rainfall is measured by a rain gauge, altitude by an altimeter and temperature by a thermometer. So statements 1, 2 and 4 describe other instruments, which rules out (A), (B) and (D) since each of them includes at least one of these.

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10.

List - I (Transducers)	List - II (Measured Quantity)
(a) Capacitive transducer	(i) Temperature
(b) Thermocouple	(ii) Power
(c) Bourdon gauge	(iii) Displacement
(d) Solar cell	(iv) Pressure

Codes :
(a) (b) (c) (d)

A.(i) (iii) (ii) (iv)
B.(iii) (i) (iv) (ii)
C.(ii) (iv) (i) (iii)
D.(iv) (i) (iii) (ii)

Exam Year(s)

UGC NET - 2013,

Answer: B

The matching is (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii), which is option (B). A capacitive transducer measures displacement through a change in plate spacing or overlap. A thermocouple measures temperature. A Bourdon gauge measures pressure through the straightening of a curved tube. A solar cell delivers electrical power from light. Options (A), (C) and (D) each swap at least two pairs, for example pairing the thermocouple with power or the Bourdon gauge with temperature.

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Classification of Transducers Questions and Answers

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