Greenlee DM210A Datasheet download pdf (Page 10)

AC Measurement

AC measurements are usually displayed as RMS (root mean square) values. The RMS value is equal to

the value of a DC waveform, which would deliver the same power if it replaced the time-varying wave-

form. Two AC measurement methods are average-responding RMS calibrated and true RMS-reading.

The average-responding RMS calibrated method takes the average value of the input signal after full

wave rectiﬁcation, multiplies it by 1.11, and displays the result. This method is accurate if the input

signal is a pure sine wave. The DM-200A and DM-210A are average-responding meters.

The true RMS-reading method uses internal circuitry to read the true RMS value. This method is accu-

rate, within the speciﬁed crest factor limitations, whether the input signal is a pure sine wave, square

wave, triangle wave, half wave, or signal with harmonics. The ability to read true RMS provides much

more measurement versatility. The DM-510A is a true RMS meter.

The Waveforms and Crest Factors table shows some typical AC signals and their RMS values.

Waveforms and Crest Factors

Waveform

RMS Value 100 100 100 100

Average Value 90 100 87 64

Crest Factor*

(x)

1.414 1 1.73 2

* The crest factor is the ratio of the peak value to the RMS value; it is represented by the Greek

letter x.

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Greenlee DM210A Datasheet Page 10