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From: Winfield Hill
Subject: Re: Watt Meter Project....Attn Win
Date: 22 Dec 2002 06:06:37 -0800
Organization: Rowland Institute
X-Newsreader: Direct Read News 4.20
R. Lewis wrote...
> You are correct in that I wrote VA as a lazy mans way of writing
> sigma di*dv but what I still cannot see is how the power in a
> reactive load can be deduced from looking only at two consecutive
> quadrants. No problem as long as the load is not reactive - make
> the assumption that the each half wave is the same as the next -
> but is it not the point with complex loads that this is not so -
> and cannot be so else they would not be complex!
> At a glance, since the claim for the circuit is that it is valid
> for complex (reactive) loads, I wondered if there was something
> clever going on that somehow predicted the non-monitored quadrants
> behaviour. On further inspection I see that it doesn't and the
> claim is invalid.
The claim is indeed valid, assuming common polarity-symmetrical
complex loads. Examining a full 360-degree calculation, one sees
two identical p(t) = i(t)*v(t) waveforms, each 180-degrees long.
The waveform may indeed be strange-looking, but it'll have two
identical segments. Therefore it's valid to ignore one of the
180-degree segments and multiply the other by two as a shortcut
to obtain power.
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