True Rms Ac Measurements - Agilent Technologies L34410A User Manual

4 Measurement Tutorial

True RMS AC Measurements

True rms responding multimeters, like the Agilent 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 Agilent 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 Agilent's ac–coupled true
rms measurements. This can provide a significant benefit.
106 34410A/11A/L4411A User's Guide