Electrical Engineering ⇒ Topic : Form Factor

There exists a definite relation among the peak value, average value and r.m.s. value of an alternating quantity. The relationship is expressed by two factors, namely ; form factor and peak factor.

(1) Form factor. The ratio of rm.s. value to the average value of an alternating quantity is known as form factor i.e.

The value of form factor depends upon the waveform of the alternating quantity. Its least value is 1 (e.g. for square wave, rectangular wave) and may be as high as 5 for other waveforms. The form factor for an alternating voltage or current varying sinusoidally is 1.11. i.e.

For a sinusoidal voltage or current,

The form factor gives a measure of the "peakiness" of the waveform. The peakier the wave, the greater is its form factor and vice-versa. For instance, a sine wave is peakier than a square wave.Hence the former has a greater form factor (1.11) than the latter. Similarly, a triangular wave is more peaky than a sine wave and has a form factor of 1.15. The form factor is useful in rectifier service.