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From: John Woodgate
Subject: Re: Meter movements
Date: Sat, 16 Nov 2002 08:00:58 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Sat, 16 Nov 2002 12:16:55 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Tony Williams
wrote (in <firstname.lastname@example.org.
uk>) about 'Meter movements', on Fri, 15 Nov 2002:
>The copper in the coil of a moving coil meter
> has a very high (positive) temperature sensitivity.
> This affects the simple I= V/R calculation,
> especially with sensitive meters. It can be
> compensated for mechanically, but that can be very
Many moving-coil meters have a 'swamp' resistor in series with the coil.
The swamp is made of wire with a very low temperature coefficient of
resistance and has a much higher resistance than the coil. So variations
in the coil resistance are 'swamped' by the fixed resistance and have
little effect on the accuracy.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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