Greenlee DM-500, Instruction Manual, Page: 9 / 76

DM-500 • DM-510
9
AC Measurement
AC measurements are usually displayed as RMS (root mean squared) values. Two methods of
AC measurement are average-responding RMS calibrated and true RMS-reading.
The average-responding RMS calibrated method takes the average value of the input signal,
multiplies it by 1.11, and displays the result. This method is accurate if the input signal is a
pure sine wave. The Greenlee DM-500 is an average-responding meter.
The true RMS-reading method uses internal circuitry to read the true RMS value. This method
is accurate, within the specified crest factor limitations, whether the input signal is a pure sine
wave, a square wave, sawtooth wave, half wave or signal with harmonics. The ability to read
true RMS provides much more measurement versatility. The DM-510 is a true RMS meter.
The Waveforms and Crest Factors table shows some typical AC signals and their RMS values.
Waveforms and Crest Factors
* The crest factor is the ratio of the peak value to the RMS value; it is represented by the
Greek letter
ξ
.
Waveform
RMS Value
Average Value
Crest Factor*
(
ξ
)
100 100 100 100
90 100 87 64
1.414 1 1.73 2