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7
Appendix
7.1 RMS and Average
Dierence between the RMS and Average
When converting AC to RMS, two methods are available, “True
RMS method (True RMS indication)” and “Average method (Average
rectifying RMS indication)”.
In the case of the sine wave where no skew is included, the same
values are indicated in both methods. However, if the waveform is
skewed, a dierence occurs between the two methods.
The true RMS method is applied to this instrument.
True RMS method
It determines RMS values of AC signals, including harmonic
components within the accuracy guarantee frequency range, and
display them.
Average method
The input waveform is handled as a sine wave where no skew is
included (only single frequency). The average of the AC signal
is obtained, converted to the RMS, and then displayed. If the
waveform is skewed, a greater measurement error occurs.
Measurement example True RMS Average rectifying RMS
100 V sine wave 100 V 100 V
100 V square wave 100 V 111 V
V m = V avg = V rmsV avg V rms
t
V (t)
V m
V (t)
t
TT
V m: Maximum value, V avg: Average value, V rms: RMS, T: Time period
Sine wave Square wave
7 Appendix
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