Question

The scale of a full wave rectifier type average sensing meter is calibrated to read the r.m.s value for ideal sine wave signal (form factor 1.11). Determine the multiplying factor of the meter if it is used to measure the r.m.s value of square waves.

• A. 1.11
• B. 1/1.11
• C. 1.0
• D. depend on the frequency of the square wave

Answer 1

The correct option is B 1/1.11

Given:
Meter reads rms value viz.
$=1.11V_{avg}forsinusoidalwave$

$\because$ For a square wave input, full wave rectifier will give DC output.


For DC output,

$V_{avg}=V_p$

$\therefore meterwillread1.11V_{avg}or1.11V_p$

$Butthetruevalueofrectifieroutputwhichwillbereadbythismeter=V_p$

Hence, correction factor

$=\frac{\text{True value}}{\text{Measured value}}=\frac{1}{1.11}$