108 34410A/11A/L4411A User’s Guide
4 Measurement Tutorial
True RMS AC Measurements
True rms responding multimeters, like the Keysight 34410A/11A/L4411A, measure the
"heating" potential of an applied voltage. Power dissipated in a resistor is proportional to
the square 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 meter’s effective bandwidth.
Note that the 34410A/11A/L4411A uses the same techniques to measure true rms
voltage and true rms current. The effective ac voltage bandwidth is
300 kHz, while the effective ac current bandwidth is 10 kHz.
The multimeter's ac voltage and ac current functions measure the ac–coupled true rms
value. In this Keysight meter, 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 is a dc voltage content, which is rejected by Keysight’s ac–
coupled true rms measurements. This can provide a significant benefit.
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