DMR35-ACV Series

AC Voltmeter

DMR35-ACV.A01.D04 Page 7 of 11

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RMS MEASUREMENT MODE VS. AVERAGE MEASUREMENT MODE.

These meters are capable of both RMS and Average Reading (RMS adjusted) measurement modes:

RMS (Root-Mean-Square) Mode – RMS voltage can be thought of as the equivalent DC voltage required to dissipate a given amount of energy in a

resistive load. Benefit of RMS measurements:



Provides an indication of delivered power, independent of the exact waveform being measured



Comparable with most high-quality handheld multimeters that tend to adapt RMS measurement

RMS Measurement Signal Flow.

Average-Reading mode – In this mode, the meter measures the average rectified value of the voltage waveform. Since the resulting measurement

is different from the RMS measurement, it is typically ‘adjusted’ to match the RMS measurement value for the case of a sinusoidal waveform. The

benefit of this measurement mode it that it enables DMR35 meters to provide measurements comparable to those provided by many electro-

mechanical analog meters. The block diagram below shows the signal-processing performed in making RMS-adjusted average mode measurements.

RMS-adjusted Average Measurement Signal Flow

Note that both measurement modes adapt a digital high-pass filter, placed after the ADC, to remove any DC bias from the input signal and generate

a signal that is symmetric about zero. As a result, these meters only measure the AC component of the input signal, and not the DC component – a

DC signal presented to the meter will read as zero. Significant amounts of DC input signal, however, may force the meter’s ADC into over-range and

reduce measurement accuracy. For this reason, the DMR35-ACVx series of meters should not be used to measure currents having a significant DC

component.

Crest Factor

When making AC measurements, the shape of the waveform to be measured can influence the measurement results. One of the most basic metrics

used to quantify waveform shape is

crest factor, which is defined as the ratio between the waveform’s peak value and its RMS value.

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