User`s guide

Measurement Tutorial 3
34450A User’s Guide 87
True RMS AC Measurements
True RMS responding multimeters, like the 34450A, measure
the “heating” potential of an applied voltage. Power
dissipated in a resistor is proportional to the square root of
an applied voltage, independent of the waveshape of the
signal. This multimeter accurately measures true RMS
voltage or current, as long as the wave shape contains
negligible energy above the instrument’s effective bandwidth.
Note that the 34450A uses the same techniques to measure
true RMS voltage and true RMS current.
The multimeter’s AC voltage and AC current functions
measure the AC- coupled true RMS value. In this Keysight
instrument, the “heating value” of only the AC components of
the input waveform are measured (DC is rejected). As seen
in the figure above; for sinewaves, triangle waves, and
square waves, the AC- coupled and AC+DC values are equal
since these waveforms do not contain a DC offset. However,
for non- symmetrical waveforms, such as pulse trains, there
Waveform Shape Crest Factor AC RMS AC + DC RMS