Hioki DT4256 - Appendix Appx; Appx. 1 RMS and Average

Appx.1
Appendix
Appx. 1 RMS and Average
Difference between the RMS and Average
When converting AC to RMS, 2 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 difference occurs between the 2 methods.
The true RMS method is applied to this instrument.
In the true RMS method, the high frequency component is also
included and displayed.
In the 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
100 V sine wave 100 V 100 V
100 V square wave 100 V 111 V
Vm=Vavg=Vrm
s
Vavg Vrms
t
V(t)
Vm
V(t)
t
TT
方形波
正弦波
Sine wave
Vm: Maximum value, Vavg: Average value, Vrms: RMS, T: Time period
Square wave
Appendix