> 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

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