Question

Which of the instruments is most accurate?

(a) PMMC

(b) Moving iron

(c) Thermo couple

(d) Induction type

This question was posed to me in an internship interview.

I'd like to ask this question from The Rectifier Voltmeter topic in section Application of Diodes of Electronic Devices & Circuits

Answer 1

Correct answer is (a) PMMC

For explanation I would say: This torque in PMMC ensures the pointer comes to an equilibrium position i.e. at rest in the scale without oscillating to give an accurate reading. In PMMC as the coil moves in the magnetic field, eddy current sets up in a metal former or core on which the coil is wound or in the circuit of the coil itself which opposes the motion of the coil resulting in the slow swing of a pointer and then come to rest quickly with very little oscillation. It has great accuracy.