Keysight Technologies 3458A Guide D'utilisation page 445

AC Volts and AC Current
The 3458A multimeter has the unique capability of offering the user three different
ways of measuring equivalent DCV heating value of an input wave form (true
root-mean-square value) : analog ACV, synchronous ACV and random ACV. The
input signal follows the track-and-hold path (see
routed into the analog AC-to-DC converter or the track-and-hold circuit.
Analog ACV
The analog ACV offers broadband 10 Hz to 2 MHz rms capability utilizing a
monolithic AC to DC converter. Its accuracy, while good, is not as good as the
synchronous ACV's; its bandwidth, while also good, is not as good as the random
or the synchronous ACV's. But, it does offer the ability to measure more
accurately, faster than either of the other methods over its measurement
bandwidth. And, it can measure either repetitive wave forms or noise signals.
Synchronous ACV
Synchronous ACV offers 1 Hz to 10 MHz bandwidth with excellent 100 ppm best
accuracy, but the input wave form must be repetitive. The reading rate is
determined by the frequency of the input wave form and the desired accuracy and
resolution. The technique is straightforward: a frequency measurement is made on
the input wave form, the decision to sample the input sequentially, or in bursts at
20 µs intervals, is made based on the value of the frequency, and the
measurements are processed statistically for the rms value. The number of
samples taken, which is a measure of the speed, is determined by the resolution
selected and also determines the accuracy of the measurement.
Random ACV
Random ACV offers the same upper measurement bandwidth that synchronous
ACV offers, but the wave form can be noise or any non-repetitive signal. Since the
resolution of the measurement is dependent upon the number of samples, this
mode of operation is the least accurate and the slowest of the ACV functions for
high resolution. Aliasing (discussed in detail in the Digitizing Product Note
3458A-2) is avoided by a random selection of sampling intervals from 20 to 40 µs
in 10 ns increments.
Keysight 3458A User's Guide
Optimizing Throughout and Reading Rate
Figure D-4) where it may be
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