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From: zben@umd5.UUCP
Newsgroups: net.consumers,net.analog
Subject: Re: power meters
Message-ID: <450@umd5.UUCP>
Date: Tue, 26-Mar-85 16:13:51 EST
Article-I.D.: umd5.450
Posted: Tue Mar 26 16:13:51 1985
Date-Received: Thu, 28-Mar-85 02:05:21 EST
References: <500@harvard.ARPA> <973@dual.UUCP> <511@harvard.ARPA>
Reply-To: zben@umd5.UUCP (Ben Cranston)
Distribution: net
Organization: U of Md, CSC, College Park, Md
Lines: 15
Xref: watmath net.consumers:2056 net.analog:232
Summary: Its a bit more complex than it seems 

Its a little more difficult than it seems, due to a concept usually called
POWER FACTOR.  This measures the fact that your load seldom acts like a
simple resistor, but more often has a reactive component.  Simply put, your
load is going to look a little bit like a capacitor or an inductor, this
depends on the load.  Motors and power transformer driven gear looks like
an inductor, florescent lights look like a capacitor.

This phenomenon causes the current sine wave to get out of phase to the
voltage sine wave.  Thus an instantanious product of voltage and current
will tend to read LESS than the actual power drawn.

The little box with the spinning wheel outside your house is specially
designed to cope with this (somehow?!) and is uncheap because of it.
-- 
Ben Cranston  ...{seismo!umcp-cs,ihnp4!rlgvax}!cvl!umd5!zben  zben@umd2.ARPA