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GATE 2025 IN – Question 14

Sensors and Industrial Instrumentation · Resistive capacitive and inductive sensors · 1 mark · Multiple choice

The primary coil of the LVDT shown is supplied with AC voltage. Its secondary coils are connected in series opposition, with output measured by a true RMS voltmeter. Core displacement $x$ is indicated in mm on a linear scale. At the null position $x=0$, the reading is 0 V. If the reading is 0.2 V for $x=+2$ mm, then the reading at $x=-3$ mm, in V, is

Diagram for GATE 2025 IN question 14
  1. −0.3
  2. −0.1
  3. 0.3
  4. 0.5

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Show answer and explanation

Correct answer: (C) 0.3

Explanation

In the linear range, output magnitude is proportional to displacement magnitude.

Sensitivity is 0.2/2=0.1 V/mm.

At −3 mm the differential signal reverses phase, but a true RMS meter reports positive magnitude: **0.3 V, C**.