Marechiare wrote:
> Imagine the device to be connected to a supply of very distorted sine
> (say square waveform of the back-up UPS).

No, since one of the assumptions for the peak picking method is that the
voltage waveform is not significantly distorted.  If the system has to deal
with distortion, then doing the full RMS calculation is pretty much required
to get the "real" voltage.

> - assume you know the amplitude of fundamental component behind the
> wave

Bad assumption, since that's basically what he's trying to measure.

> Total of instantaneous squared values for the cycle IS low pass
> filtered by the very process of addition the values, isn't it?

No, that is a integral.  In the long run the AC components will sum to 0 and
you will be left with the integral of the DC component, which is a
infinitely increasing value for any non-zero DC offset.

> High frequency distortions are unlikely after the transformer,
> I think.

But wait, your earlier argument was exactly the opposite: "Imagine the
device to be connected to a supply of very distorted sine".  You can't have
it both ways.  In the end, only Dario can answer whether the mostly sine
approximation is valid in his case.


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