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Re: [T2] Re: thermocouples

From: Nigel A. Skeet
To: Dan et al
Date: 16th September 2001
Reply to: naskeet@xxxxxxxxxxx
According to the law of intermediate metals for thermocouples, your two junctions with the copper extension wires, should be at the same temperature, in order not to contribute their own nett voltage signal. 
Instead of using ordinary copper wire, I have used foil & copper braided, 
low-low, screened, twisted-pairs cable (as used in computer networks and 
telecommunications) to minimise capacitive and inductive signal noise. This 
is coonected at either end using 5-pin audio DIN plugs.

Regards.
       Nigel A. Skeet


From: Dan <vw_bus_74@xxxxxxxxx>
To: type2@xxxxxxxxx
Subject: [T2] Re: thermocouples
Date: Mon, 10 Sep 2001 14:36:33 -0700 (PDT)


Thermocouples are made from dissimilar metals (2) joined at
one end. They produce a small unique voltage at a given
temperature. IF you add regular copper wire into the ckt
make sure it is the same size for both legs. Splice it in
so that you are going into your meter with the thermocouple
wire.
                     splice      splice
thermocouple-----------[]---------[]---------------meter
            thermowire   Cu wire     thermowire

the splice(s) should be in an area where there is no large
temperature difference between them. This insures that the
splice error contribution cancels out.

  In Short : A thermocouple produces it's own voltage. It
is  a thermoelectric voltage produced at the junction of
two dissimilar metal wires when heated/cooled and is
interperated by a thermocouple thermometer (guage).
  Don't add on regular wire at the end. Splice a length
into the overall length and run thermocouple wire into your
guage.

>I just purchased and *almost* installed a VDO cylender
head temp gauge.
>I am assuming that this gauge isnt nuclear powered and
will require
>power.
>So how does this bubba hook up?

As a matter of fact, it is nuclear powered. Seriously, I
don't know what
powers it, but no 12 volt power is required.
VDO has a website with instructions for all their gauges.



=====
Dan (close to Seattle)

Think for yourself and let others enjoy
the privilege of doing so too.
                               Voltaire

http://www.geocities.com/MotorCity/Speedway/1974/index.html

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