>> 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.

Have you noticed that Dario said about a pump to be monitored,
Normally this kind of rugged devices are expected to deal with bad
voltage waveform.


>> - assume you know the amplitude of fundamental component
>> behind the wave
>
> Bad assumption, since that's basically what he's trying to measure.

Have you noticed the last step in the iterative algorithm? The
statement you quoted was first step of the algorithm. The last step
was:

"- based on these 4 values adjust amplitude/phase/frequency of the
imaginary fundamental component to be used in the next cycle;"

In a few cycles the amplitude will be adjusted close to the "right"
value. Your filter coefficients seem to get few cycles to set up too.


>> 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.

Have you noticed "squared" word in the statement?
Under "squared" I meant the value to multiply the by itself. Did you
use some other math terminology in the school? The squared AC
component values are always positive, aren't you getting it? How is
you rant about integrating the AC components related to integrating
squared AC component values?


>> 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". =A0You can't have it both ways.

Have you noticed "High frequency" phrase in the statement? The
waveform of the sine after the transformer could be heavily distorted,
but still there can be very little high frequency noise. I talked
about high frequency distortions because of your concern that low pass
filtering should be applied even for RMS method.

-- =

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