Average value, RMS Value, Form factor and Peak factor for different waveforms:
Sinusoidal wave:
A sinewave is defined by the trigonometric sine function. When plotted as
voltage (V) as a function of phase (θ), it looks similar to the figure to the below. The
waveform repeats every 2p radians (360°), and is symmetrical about the voltage axis (when
no DC offset is present). Voltage and current exhibiting cyclic
behavior is referred to as
alternating; i.e., alternating current (AC). One full cycle is shown here. The basic equation for
a sinewave is as follows:
There are a number of ways in which the amplitude of a sinewave is
referenced, usually as
peak voltage (V
pk
or V
p
), peak-to-peak voltage (V
pp
or V
p-p
or V
pkpk
or V
pk-pk
), average
voltage (V
av
or V
avg
), and root-mean-square voltage (V
rms
). Peak
voltage and peak-to-peak
voltage are apparent by looking at the above plot. Root-mean-square and average voltage are
not so apparent.
Average Voltage (V
avg
)
As the name implies, V
avg
is calculated by taking the average of the voltage in
an appropriately chosen interval. In the case of symmetrical waveforms like the sinewave, a
quarter cycle faithfully represents all four quarter cycles of the waveform. Therefore, it is
acceptable to
choose the first quarter cycle, which goes from 0 radians (0°) through p/2
radians (90°).
As with the V
rms
formula,
a full derivation for the V
avg
formula is given here as well.
