Resistive Transducers Questions and Answers

Q: Strain gauge is a/an :

A strain gauge is a passive device that converts mechanical displacement into a change of resistance.A strain gauge is a fine wire or foil grid bonded to a surface. When the surface is strained, the grid stretches or compresses, changing its length, cross-section and resistivity, and so its resistance; the gauge factor relates the fractional change in resistance to the strain.It is passive because it generates no energy of its own: an external excitation, usually a Wheatstone bridge, is needed to turn the resistance change into a voltage. The options calling it active describe a self-generating transducer such as a thermocouple or piezoelectric crystal, and 'electrical displacement' is not what it senses.

Q: The drawbacks of strain gauges are :S1 : Low fatigue lifeS2 : They are expensive, brittle and sensitive to temperatureS3 : Poor linearity

The official key is S2 and S3: the gauges are brittle and temperature sensitive, and they show poor linearity.These two points describe semiconductor strain gauges, which have a large gauge factor but whose resistance changes non-linearly with strain, drift with temperature and are brittle and hard to bond. Sources found for the search agree on brittleness, temperature sensitivity and non-linearity.What could not be confirmed: sources disagree on the cost of semiconductor gauges, which some call low and some high, and 'low fatigue life' (S1) was not found among the usual listed drawbacks. The key's S1-free answer, S2 and S3, is therefore kept; options containing S1 are rejected on that basis.

Q: Semiconductor strain gauges depend upon ................. for their action.

Semiconductor strain gauges depend on the piezo-resistive effect.When silicon or germanium is strained, its band structure and carrier mobility change, so its resistivity changes. This change in resistivity is far larger than the purely geometric change in a metal-foil gauge, giving gauge factors of roughly 100 to 175 against about 2 for metal gauges. The resistance change is read in a Wheatstone bridge.The piezoelectric effect generates a charge rather than changing resistance, and suits dynamic rather than static strain. Ferromagnetism is the basis of magnetostrictive sensors, and superconductivity plays no part in strain gauges.

Q: Strain gauge is a :

A strain gauge is a passive device and converts mechanical displacement into a change of resistance.A strain gauge is a fine metal foil or wire, or a semiconductor element, bonded to a structure. When the structure is strained, the gauge's length and cross-section change, and so its resistance changes in proportion to the strain, by a factor called the gauge factor. It produces no energy of its own and needs an external excitation, normally through a Wheatstone bridge, so it is a passive transducer.Options calling it active are wrong, since active transducers, such as thermocouples and piezoelectric crystals, generate their own output. 'Electrical displacement' is wrong because the input is mechanical strain.

Q: A Wheatstone bridge is commonly used in biomedical transducers for

A Wheatstone bridge is used for strain gauge-based pressure measurement.A strain gauge changes its resistance by only a tiny fraction when strained. Placed in a Wheatstone bridge, often with four active gauges on a diaphragm, that small change unbalances the bridge and gives a voltage proportional to pressure, with temperature effects largely cancelled. Disposable invasive blood pressure transducers work this way.ECG amplification uses instrumentation amplifiers, not a bridge. Optical imaging uses photodetectors, and ultrasound is generated by driving piezoelectric crystals.

Direction for [ Question No: 1 To 1 ] :

Directions : The following items consist of two statements, one labelled the "Assertion (A)" and the other labelled the "Reason (R)". You are to examine these two statements carefully and decide if the Assertion (A) and the Reason (R) are individually true and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below and mark your answer accordingly.

Assertion (A) : To have a high sensitivity, a low value of gauge factor is desirable.
Reason (R) : Semi-conductor strain gauges are made up of Si and Ge and show piezo-resistive effect.

A.Both (A) and (R) are correct and (R) is correct explanation of (A).
B.Both (A) and (R) are correct, but (R) is not correct explanation of (A).
C.(A) is true, but (R) is false.
D.(A) is false, but (R) is true.

Exam Year(s)

UGC NET - 2014,

Answer: D

The Assertion is false and the Reason is true. A high gauge factor, not a low one, gives a high sensitivity, because the gauge factor is the ratio of the fractional change of resistance to the strain. Semiconductor strain gauges made of silicon or germanium show the piezo-resistive effect and have gauge factors much larger than metallic gauges, so they are chosen for sensitivity.

Hence the Reason is a correct statement, but the Assertion contradicts the meaning of gauge factor.

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Strain gauge is a/an :

A.Active device and converts mechanical displacement into a change of resistance.
B.Passive device and converts electrical displacement into a change of resistance.
C.Passive device and converts mechanical displacement into a change of resistance.
D.Active device and converts electrical displacement into a change of resistance.

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: C

A strain gauge is a passive device that converts mechanical displacement into a change of resistance.

A strain gauge is a fine wire or foil grid bonded to a surface. When the surface is strained, the grid stretches or compresses, changing its length, cross-section and resistivity, and so its resistance; the gauge factor relates the fractional change in resistance to the strain.

It is passive because it generates no energy of its own: an external excitation, usually a Wheatstone bridge, is needed to turn the resistance change into a voltage. The options calling it active describe a self-generating transducer such as a thermocouple or piezoelectric crystal, and 'electrical displacement' is not what it senses.

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The drawbacks of strain gauges are :

S1 : Low fatigue life
S2 : They are expensive, brittle and sensitive to temperature
S3 : Poor linearity

A.S1 and S2
B.S2 and S3
C.S1 and S3
D.S1 only

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: B

The official key is S2 and S3: the gauges are brittle and temperature sensitive, and they show poor linearity.

These two points describe semiconductor strain gauges, which have a large gauge factor but whose resistance changes non-linearly with strain, drift with temperature and are brittle and hard to bond. Sources found for the search agree on brittleness, temperature sensitivity and non-linearity.

What could not be confirmed: sources disagree on the cost of semiconductor gauges, which some call low and some high, and 'low fatigue life' (S1) was not found among the usual listed drawbacks. The key's S1-free answer, S2 and S3, is therefore kept; options containing S1 are rejected on that basis.

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Semiconductor strain gauges depend upon ................. for their action.

A.Piezoelectric effect
B.Piezo-resistive effect
C.Ferro-magnetic
D.Superconductivity

Exam Year(s)

MH SET - 2024, SET Exam - 2024,

Answer: B

Semiconductor strain gauges depend on the piezo-resistive effect.

When silicon or germanium is strained, its band structure and carrier mobility change, so its resistivity changes. This change in resistivity is far larger than the purely geometric change in a metal-foil gauge, giving gauge factors of roughly 100 to 175 against about 2 for metal gauges. The resistance change is read in a Wheatstone bridge.

The piezoelectric effect generates a charge rather than changing resistance, and suits dynamic rather than static strain. Ferromagnetism is the basis of magnetostrictive sensors, and superconductivity plays no part in strain gauges.

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Strain gauge is a :

A.active device and converts mechanical displacement into a change of resistance
B.passive device and converts electrical displacement into a change of resistance
C.passive device and converts mechanical displacement into a change of resistance
D.active device and converts electrical displacement into a change of resistance

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: C

A strain gauge is a passive device and converts mechanical displacement into a change of resistance.

A strain gauge is a fine metal foil or wire, or a semiconductor element, bonded to a structure. When the structure is strained, the gauge's length and cross-section change, and so its resistance changes in proportion to the strain, by a factor called the gauge factor. It produces no energy of its own and needs an external excitation, normally through a Wheatstone bridge, so it is a passive transducer.

Options calling it active are wrong, since active transducers, such as thermocouples and piezoelectric crystals, generate their own output. 'Electrical displacement' is wrong because the input is mechanical strain.

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A Wheatstone bridge is commonly used in biomedical transducers for

A.ECG signal amplification
B.Optical imaging
C.Ultrasonic signal generation
D.Strain gauge-based pressure measurement

Exam Year(s)

Tripura Public Service Commission - 2026,

Answer: D

A Wheatstone bridge is used for strain gauge-based pressure measurement.

A strain gauge changes its resistance by only a tiny fraction when strained. Placed in a Wheatstone bridge, often with four active gauges on a diaphragm, that small change unbalances the bridge and gives a voltage proportional to pressure, with temperature effects largely cancelled. Disposable invasive blood pressure transducers work this way.

ECG amplification uses instrumentation amplifiers, not a bridge. Optical imaging uses photodetectors, and ultrasound is generated by driving piezoelectric crystals.

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A Resistance strain gauge has gauge factor of 2. It is connected to a steel member which is subjected to a strain of \(1 \times 10^{-6}\). If the original resistance value of the gauge is 130 \(\Omega\), what is the change in resistance ?

A.130 \(\mu\Omega\)
B.390 \(\mu\Omega\)
C.260 \(\mu\Omega\)
D.520 \(\mu\Omega\)

Exam Year(s)

UGC NET - 2012,

Answer: C

The change in resistance of the strain gauge is 260 micro-ohm. The gauge factor is the fractional change in resistance divided by the strain, so

\[ G = \frac{\Delta R / R}{\varepsilon} \]
\[ \Delta R = G\,\varepsilon\,R \]
\[ \Delta R = 2 \times 10^{-6} \times 130\ \Omega \]
\[ \Delta R = 260\times10^{-6}\ \Omega = 260\ \mu\Omega \]

The value 130 micro-ohm would be the answer with a gauge factor of 1, and 390 and 520 micro-ohm would correspond to gauge factors of 3 and 4. The answer is 260 \(\mu\Omega\).

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The gauge factor of a resistance wire strain gauge is a measure of

A.Sensitivity of the gauge
B.Resolution
C.Dynamic range of displacement measurement capability
D.Variable inductance

Exam Year(s)

UGC NET - 2013,

Answer: A

The gauge factor is a measure of the sensitivity of the gauge. It is defined as the fractional change in resistance per unit strain, \(GF = (\Delta R/R)/(\Delta L/L)\), so a larger gauge factor means a larger electrical output for the same mechanical strain. Resolution (B) is the smallest change in the measured quantity that can be detected, which depends on the instrumentation as well. Dynamic range (C) is the span of displacements the gauge can follow. Variable inductance (D) is the principle of a different transducer, not a property of a resistance wire gauge.

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A displacement transducer with a shaft stroke of 3.0 cm, is applied to as shown in figure. The total resistance of the potentiometer is 5 k Ω. The input voltage is 5 V, when the wiper is at 0.9 cm. The value of the output voltage is given by

Potentiometer connected across the input voltage Vin between points A and B; the wiper arm takes the output voltage Vout, with R1 the part above the wiper and R2 the part below it

A.1.5 V
B.15 V
C.0.15 V
D.5 V

Exam Year(s)

UGC NET - 2013,

Answer: A

The output voltage of the potentiometer is the input voltage multiplied by the fraction of the stroke at which the wiper stands. The wiper is at 0.9 cm out of a 3.0 cm stroke, so

\[V_{out} = V_{in} \times \dfrac{0.9}{3.0} = 5 \times 0.3\]

\[V_{out} = 1.5\ \text{V}\]

The output is thus 1.5 V, the first option. The potentiometer only divides the input, so the output cannot exceed 5 V, which rules out 15 V, and 5 V would need the wiper at the very top. A value of 0.15 V is a factor of ten too small.

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10.

An angular position to be measured using a transducer. Which of the following types of transducers can be used for this purpose ?

1. Circular potentiometer
2. LVDT
3. E-pick off
4. Synchro
Select the correct answer using the codes given below :
Codes :

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

Exam Year(s)

UGC NET - 2014,

Answer: D

The keyed answer is 1 and 4. A circular potentiometer gives a voltage that varies with the angle of its wiper, and a synchro gives output voltages that depend on the shaft angle, so both measure angular position directly.

An LVDT is a linear displacement transducer: its core moves along a straight line, so it does not measure a rotation by itself. That removes the options that include 2. The E-pick off is a small-displacement inductive pick-off; the key does not treat it as an angular position transducer, so the options with 3 are rejected. This question is accepted as keyed, but reviewers may wish to check the treatment of the E-pick off.

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Resistive Transducers Questions and Answers

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