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From: paul@dual.UUCP (Baker)
Newsgroups: net.consumers,net.analog
Subject: Re: power meters
Message-ID: <974@dual.UUCP>
Date: Tue, 26-Mar-85 12:03:21 EST
Article-I.D.: dual.974
Posted: Tue Mar 26 12:03:21 1985
Date-Received: Wed, 27-Mar-85 04:40:05 EST
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Xref: watmath net.consumers:2045 net.analog:222

> 
> Before you insult somebody because of his "ignorance", you should be sure that
> you are not ignorant yourself. An ammeter won't work to measure AC power, even
> with constant voltage.  This is because AC power equals RMS voltage times
> RMS current times the cosine of the phase angle between them.

This is strictly speaking true. However

1) Most devices are designed to have a power factor close to one.  In
   this case the power consumed does equal scalar voltage times scalar
   current.  For example flourescent lamps have a capacitor solely for
   power factor correction.
2) Domestic electricity meters measure scalar voltage times current and
   the person in question was interested in optimizing for minimum
   electricity bill and not particularly for minimum power.
> 
> Power meters do exist.  I'm not sure where to get them, though.
>
Paul Wilcox-Baker.