Re: True RMS and averaging.

John O'Flaherty <quiasmox@xxxxxxxxx> wrote:
(snip)

< If it's a power line, and you know the period, wouldn't you know the
< phase as well? I wonder if you could continuously sample, and make a
< comparison of each sample to the appropriate level of current at that
< point in the cycle, rather than an average RMS value. Then if n
< sequential samples exceed their appropriate thresholds, trip.

I presume you would know the phase of the voltage, but for
reactive loads with changing reactance, you might not know the
current phase. It seems that the OP is measuring current.

Within roundoff and the bits available, it seems that you should
be able to do a fixed point decaying average with the appropriate
time constant, assuming a reasonable sampling rate. I do agree
that you have to be careful to make sure that the result comes out
as desired.

-- glen
.

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