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TRUE RMS (DM-531T, DM-532T)
In order to compare dissimilar waveform, calculate ohm's law statements or power relationship, you
must know the effective value of a signal.
If it is a dc signal, the effective value equals the dc level.
If the signal is ac, however, we have to use the root mean square or rms value. The rms value of an ac
current or ac voltage is defined as being numerically equal to the dc current or voltage that produces the
same heating effect in a given resistance that the ac current or voltage produces.
In the past, average responding converters were the type of converter most widely used. theoretically, the
rms value of a pure sine wave is 1/2 of the peak value and the average value is 2/
of the peak value.
Since the meters converted to the average value, the value was 1/2
2/
= 1.11 of the average value
when measuring a sine wave. Most meters used an average responding converter and multiplied 1.11 to
present true rms measurements of sine waves.
As the signal being measured deviated from a pure sine waves, the errors in measurement rose sharply.
Signals such as square waves, mixed frequencies, white noise, modulated signals, etc., could not be
accurately measured.
Rough correction factors could be calculated for ideal waveforms if the signal being measured was
distortion free, noise-free, and a standard waveform. The true rms converter in this meter provides direct
accurate measurement of these and other signals.
