Agilent Technologies Truevolt Series Operating And Service Manual page 90

True RMS AC Measurements
True rms responding multimeters, like the Agilent Truevolt Series, 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 Agilent Truevolt Series 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 DMM's AC voltage and AC current functions measure the AC-coupled true rms value. In this DMM, the "heating
value" of only the AC components of the input waveform are measured (dc is rejected). As seen in the figure above; for
sine waves, triangle waves, and square waves, the AC–coupled and AC+DC values are equal, because 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.
An AC–coupled true rms measurement is desirable when you are measuring small AC signals in the presence of large
DC offsets. For example, this situation is common when measuring AC ripple present on DC power supplies. There are
situations, however, where you might want to know the AC+DC true rms value. You can determine this value by
combining results from DC and AC measurements, as shown below:
For the best AC noise rejection, you should perform the DC measurement using an integration time of at least 10
power–line cycles (PLCs).
90 Agilent Truevolt Series DMM Operating and Service Guide