Which of the following measurement instruments consumes the least amount of energy?

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SSC JE Electrical 11 Oct 2023 Shift 3 Official Paper-I
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  1. Induction type
  2. Dynamometer type
  3. PMMC type
  4. Moving iron type

Answer (Detailed Solution Below)

Option 3 : PMMC type
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Permanent Magnet Moving Coil (PMMC)

PMMC is used to measure an average DC value of electrical quantity.

PMMC-type measurement instrument typically consumes the least amount of energy among the options provided. PMMC instruments are known for their high sensitivity and low power consumption.

They use a permanent magnet and a moving coil to measure the electrical quantity, and the energy required to move the coil is relatively low compared to some other types of instruments.

The PMMC instrument has a linear scale, hence the deflecting torque produced is directly proportional to the current.

\(\tau_d=BINA\)

The controlling torque in PMMC instruments can be produced by either spring control or gravity control.

For spring control: Tc ∝ θ  and For gravity control: Tc ∝ sin θ 

Moving iron instrument

MI instruments are used for measuring the RMS value of the current or voltage.

Deflecting torque in the MI instrument is given by \(T_d={1\over 2}I^2{dL\over d\theta}\)

Since deflection is nonlinear, the scale of a moving-iron meter must be nonlinear.

Induction type instrument

Induction-type instruments are devices used for measuring electrical quantities, such as voltage and current. These instruments operate on the principle of electromagnetic induction, which was discovered by Michael Faraday. 

Electrodynamometer type instrument

The electrodynamometer is a transfer-type instrument. A transfer-type instrument may be calibrated with a DC source and then used without modification to measure AC. This requires the transfer type instruments to have the same accuracy for both DC and AC.

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