Which category of instruments does an ohmmeter fall under?

This question was previously asked in
RRB ALP Electronics Mechanic 23 Jan 2019 Official Paper (Shift 3)
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  1. Moving resistance instrument
  2. Dynamometer instrument
  3. Moving coil instrument
  4. Moving iron instrument

Answer (Detailed Solution Below)

Option 3 : Moving coil instrument
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Detailed Solution

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Concept:

Ohmmeter:

A device that measures the resistance directly is called an ohmmeter.

The simplest direct reading ohmmeter is the basic series ohmmeter circuit shown in Fig. below (A and B are the terminals of ohmmeter).

It consists of a permanent magnet moving coil (PMMC) instrument in series with a battery and a rheostat R.

(i) With terminals A and B shorted together, R is adjusted for full-scale deflection (FSD).

Since terminals A and B are shorted, the ohmmeter should read zero resistance.

FSD Current (Ig) = 

(ii) When terminals A and B are open-circuited, the pointer should indicate infinity. Therefore, zero deflection point on the scale is marked as infinite resistance.

(iii) When an unknown resistance Rx is connected to terminals A and B, the meter current Im is

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