Sanwa CD731 - Page 40

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［Caution for ACV measurement of CD731］
●Since this instrument employs the means value system for its AC
voltage measurement circuit, AC waveform other than sine wave
may cause error.
●There occurs error under such frequencies other than specified
specification.
［Caution for ACV measurement of CD751］
●True Root Mean Square Value
When measurement is taken by "average value detection r.m.s.",
no error is caused as the input signal is sine wave with no distortion.
However, if the input waveform is distorted sine wave or non-
sinusoidal wave, conversion to root mean square values is very
difficult, resulting in a large error.
When measurement is taken by true r.m.s., the measurement value
of input signal becomes the scale of the signal power and therefore
provide more effective values than those obtained by average value
detection. This multimeter imploys this true RMS (Root Mean
Square) circuit, which enables measurement of sine wave and non-
sinusoidal waves like square wave and triangular wave in r.m.s.
●Crest Factor
The crest factor (CF) is expressed by a value obtained by dividing
the peak value of the signal by its RMS value. Most common
waveforms such as sine wave and triangular wave have a relatively
low crest factor. Waveforms similar to a pulse train of low duty
cycle have a high crest factor. The voltages and crest factors of
typical waveforms are shown in the table.
Note that measurement should be taken with the crest factor
below 3.
Input Waveform
0 to Peak
P
RMS value
Vrms
Average
value Vavg
Crest factor
P/Vrms
Form factor
P/Vrms / Vavg
Sine
wave
Square
wave
Triangular
wave
Pulse
D＝―
T
2
T
1
1.414 1.000 0.900 1.414 1.111
1.000 1.000 1.000 1 1.000
1.732 1.000 0.866 1.732 1.155
2.000 2 D 2・D ――
√
1
√D
1
√D
Voltages and Crest Factors of Various Waveforms
●It may malfunction when measuring voltage/current in the
inverter circuit.