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Path: utzoo!watmath!clyde!burl!ulysses!harpo!decvax!cca!ima!inmet!dwp
From: dwp@inmet.UUCP
Newsgroups: net.physics
Subject: Re: Orphaned Response - (nf)
Message-ID: <1149@inmet.UUCP>
Date: Sat, 24-Mar-84 00:09:46 EST
Article-I.D.: inmet.1149
Posted: Sat Mar 24 00:09:46 1984
Date-Received: Sun, 25-Mar-84 13:08:34 EST
Lines: 20

#R:sri-arpa:-1712200:inmet:7600006:177600:955
inmet!dwp    Mar 22 10:57:00 1984

This is an educated guess, based on the electric blanket control
I pulled apart many years ago.  The lumps in the blanket itself
are thermostats, but they are only safety devices to prevent hot spots.
The actual control of the blanket is independent of the actual
temperature of the blanket.  It is done, apparently, by a bimetallic
strip in the control itself.  The blanket current flows through
the strip, heating it.  When it heats sufficiently, it pulls away
from an electrical contact, and the strip, and the blanket, cools.
Turning the heat control rotates a screw adjusting the gap between
the bimetallic strip and the contact, varying the amount of heating
necessary before the contact breaks.  All the feedback is in the
control itself, there is no detection of the temperature of the 
blanket.  So adding blankets over an electric blanket will make it
"too warm", until you adjust the control.
	
					David Pachura
					decvax!cca!ima!inmet!dwp