>
> > If your line frequency is well known you can just go by
> time.  But if
> > the frequency varies you may have more or less than one
> cycle.  If you
> > have 110% of a cycle the voltage you get depends on where
> in the cycle
> > you started.  If the extra 10% was near a zero crossing you
> will read
> > low.  If it was near a peak you will read high.
>
> OK, I can't really argue with that.  But, I was
> "ASS-U-ME'ing" that he was
> able to find the period of the waveform.  Given that, it
> shouldn't matter
> where you start measuring.
>
> Using your argument, I would tend to think that starting the
> measurement at
> (or near) the voltage extremes would give the most accurate
> results, since
> the delta/time is smaller here.  At zero crossing it is
> changing fastest of
> all.  So by missing the zero crossing by a few percent would
> seem to give a
> bigger error than missing the peaks/valleys by a few percent,
> just because
> the slope is so steep.  But then again IANAEE.  ;-)
>
> michael brown

You have a point about using the peak instead of the zero, but zero
crossings are easier to find.  Also once you square the result missing
one small sample is minor, missing one big sample is not.

Sherpa Doug

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