Question

A PMMC meter rated at 100 $\mu$A is used in a rectifier type of instrument which uses full wave rectification. What is the sensitivity on sinusoidal AC?

• A. 4.5 k$\Omega$/V
• B. 18 k$\Omega$/V
• C. 10 k$\Omega$/V
• D. 9 k$\Omega$/V

Hint:

Always divide DC sensitivity by 1.11 to get AC sensitivity when full-wave rectification is used on sinusoidal inputs.

Answer 1

The Correct Option is D

The DC sensitivity ($S_{DC}$) of a PMMC meter is given by:
$S_{DC} = \dfrac{1}{I_{full-scale}} = \dfrac{1}{100 \times 10^{-6}} = 10\,k\Omega/V$
For full wave rectification with sinusoidal AC, the sensitivity becomes:
$S_{AC} = \dfrac{S_{DC}}{1.11}$
$S_{AC} = \dfrac{10\,k\Omega/V}{1.11} \approx 9\,k\Omega/V$
Hence, the sensitivity on sinusoidal AC is 9 k$\Omega$/V.