PPA5xx/15xx user manual
11-1
11 True RMS Voltmeter
The RMS voltmeter displays the additional secondary
parameters of ac, crest factor, surge, mean and form
factor:
Having computed the true rms and the dc component, the
ac component can be derived from:
rms
2
= ac
2
+ dc
2
=> ac
2
= rms
2
– dc
2
Crest factor is derived from the peak and rms:
cf = peak / rms
In order to measure surge conditions, the maximum
instantaneous peak value (unfiltered) is also recorded. It is
important that the PPA5xx/15xx does not autorange
while measuring surge – either set the range to manual or
repeat the test several times with ranging set to up only.
To reset the maximum, press TRIGGER.
The mean value, also known as rectified mean, is
computed by the arithmetic mean of the absolute value of
the samples:
2
mean = 1/2
|v()| d
0
For a sampled signal, the formula becomes:
i = n-1
mean = 1/n
|v[i]|
i = 0
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