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GATE 2023 IN Q.14: solution and answer

GATE 2023 · INQ.14 · 1 mark · MCQ

Pair the quantities (p) to (s) with the measuring devices (i) to (iv).

Devices: (i) Linear Variable Differential Transformer (LVDT); (ii) Thermistor; (iii) Strain gauge; (iv) Diaphragm.
Quantities: (p) Torque; (q) Pressure; (r) Linear position; (s) Temperature.

GATE 2023 IN question 14: A two-column table.Tap to open full size
Figure from the GATE 2023 IN paper. It is part of the question.
Figure description

A two-column table. Left column: (i) Linear Variable Differential Transformer (LVDT), (ii) Thermistor, (iii) Strain gauge, (iv) Diaphragm. Right column, in the same rows: (p) Torque, (q) Pressure, (r) Linear position, (s) Temperature. The rows are not matched; the task is to pair them.

  1. (A)

    (i) - (r), (ii) - (s), (iii) - (q), (iv) - (p)

  2. (B)

    (i) - (p), (ii) - (s), (iii) - (r), (iv) - (q)

  3. (C)

    (i) - (r), (ii) - (s), (iii) - (p), (iv) - (q)

  4. (D)

    (i) - (q), (ii) - (s), (iii) - (p), (iv) - (r)

Answer and solution

ANSWER

Option (C): (i)-(r), (ii)-(s), (iii)-(p), (iv)-(q).

Official answer: CSource: Official answer key, GATE 2023 IN (IIT Kanpur)

  1. LVDT. Moving the core changes the difference between the two secondary voltages, and that difference is proportional to the core displacement. So (i) pairs with (r), linear position.

  2. Thermistor. Its resistance depends strongly on temperature, . So (ii) pairs with (s), temperature.

  3. Diaphragm. A pressure difference deflects the diaphragm, and the deflection is sensed by a secondary element. So (iv) pairs with (q), pressure.

  4. Strain gauge. The only quantity left is (p), torque. Gauges bonded on a twisted shaft sense the surface strain, with gauge factor , and so measure torque. So (iii) pairs with (p). The pressure and position quantities are already taken by the diaphragm and the LVDT.

  5. Check the options. The pairing is (i)-(r), (ii)-(s), (iii)-(p), (iv)-(q). (A) puts the diaphragm with torque and the strain gauge with pressure. (B) puts the LVDT with torque. (D) puts the LVDT with pressure and the diaphragm with linear position. Only (C) matches.

KEY IDEA

Match each device to the quantity it is designed to sense, starting with the unambiguous ones (LVDT for displacement, thermistor for temperature, diaphragm for pressure). The strain gauge then takes the one left, torque, through the strain it senses on a twisted shaft.

WATCH OUT FOR

Pairing the strain gauge with pressure because pressure transducers often use strain gauges. Here the diaphragm is the pressure-sensing element, and the strain gauge fits torque. The other slip is pairing the LVDT with torque or pressure instead of linear displacement.

From the GATE 2023 IN paper. Every question of this paper · Download the full paper · All 19 Sensing principles questions, with notes

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