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From: dam@cs.glasgow.ac.uk (Mr David Morning)
Newsgroups: sci.electronics
Subject: Re: Meters and RMS, was: Powerline voltage too high...
Message-ID: <7303@vanuata.cs.glasgow.ac.uk>
Date: 3 Jan 91 16:53:46 GMT
References: <5402@rsiatl.Dixie.Com> <9839@as0c.sei.cmu.edu> <10003@pasteur.Berkeley.EDU>
Reply-To: dam@cs.glasgow.ac.uk (Mr David Morning)
Organization: Comp Sci, Glasgow Univ, Scotland
Lines: 17

I've never really understood why the term "root mean square"(RMS) is applied to
power measurements.

Power = (V)rms*(I)rms would imply to me that 2 roots are being mutiplied
together leaving just a mean squared value.

Similarly Power= (I)rms^2 * R cancels the the "r" of the "rms"

I used to work for a firm which manufactured AC digital panel meters.
The only time I've heard the term "True RMS" used was in relation to a digital
multimeter that incorporated a true RMS chip. This chip prformed all sorts
of convoluted analogue maths to arrive at the answer. Might have used Simpsons
rule or something similar but all the other AC meters were termed "Average
Sensing, RMS scaled".

Dave
"