Date:         Wed, 12 Oct 1994 13:31:19 -0700 (PDT)
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         H Steven Dolan <dworkin@netcom.com>
Subject:      Re: cyl head temp gauge

Cylinder head temperature guages (and most other high temperature measuring 
devices) use thermocouples as sending units.  A thermocouple is a 
junction between two dissimilar metals.  When this junction is heated, 
electrons pass from one metal to the other. Moving electrons = electric 
current.  The greater the heat, the greater the current.  If you hook a 
milliamneter to the output wires and calibrate it in degrees, you get a 
temperature guage, with no outside current input.  As the current is 
teeny even at high temperatures, the resistance of the lead wires must be 
included in the calibration.  If you add to or subtract from the wires, 
you will change the resistance, and thus the temperature reading.  And 
now, back to our program....

					H Steven Dolan
					dworkin@netcom.com