From: John Woodgate
Subject: Re: Watt Meter Project....Attn Win
Date: Sun, 22 Dec 2002 23:08:46 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Mon, 23 Dec 2002 07:46:25 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Winfield Hill
wrote (in ) about 'Watt Meter
Project....Attn Win', on Sun, 22 Dec 2002:
>John Woodgate wrote...
>> I think it's OK if there are only two zero-crossings per
>> half-cycle of the fundamental - at 0 and 180 deg.
> I disagree, see above argument. If you agree that the 360-degree
> calculation produces an instantaneous true-power waveform with two
> identical segments,
Do they have to be identical?
>then using 50% of this waveform should work no
> matter what 50% portion is selected, i.e. no matter what the phase
> shift is wrt either voltage or current zero crossings. The LM394
> circuit takes its 50% based on the voltage zero crossings. :>)
What bugs me is how you define a 'half-cycle' if there are several zero-
crossings. The circuit cannot 'see' anything of the negative part of the
waveform, so how does it 'know' what happens between zero-crossings.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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