5: Basic Digital Multimeter (DMM) Operation Series 3700 System Switch/Multimeter
-10 Document Number: 3700S-900-
Figure 5-6: ACV measurements: square, pulse, and sawtooth waves
The Series 3700 is an AC-coupled RMS meter. For an AC waveform with DC content, the DC
component is removed before the RMS is calculated. This affects the crest factor because the
peak value for the DC-coupled waveform is different than the peak value for the AC-coupled
waveform. In an AC-coupled waveform, the peak value is measured from the original DC
average value, not DC zero. For example, if a voltage pulse is measured on the AC function of
the Series 3700 with a peak voltage of VP and a low voltage of zero volts, the AC-coupled peak
value will be calculated as follows:
ACPEAK = VP • (1 - duty cycle)
Therefore, the AC-coupled crest factor will differ from the DC-coupled waveform. The RMS
function will calculate the RMS value based on the pulsed waveform with an average value of
zero.
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