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Thermal couples - Page 2

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Posted by Duane C. Johnson on November 10, 2003, 4:55 am
 
Hi Mitch;



I have about 6000' of type K 24 gauge.
Want some to try it out.
I can attest to the battery carbon rod welder method.
Also have used pencil lead for thermocouples in the lab.


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Posted by Steve Spence on November 10, 2003, 2:22 pm
 
those electric coolers use a peltier module that has an interesting
characteristic. they get hot on one side, cold on the other. reverse the
polarity, and you reverse the heat flow.

http://ww2.green-trust.org:8383/thermoelectric.htm

--
Steve Spence
Renewable energy and sustainable living
http://www.green-trust.org
Donate $0 or more to Green Trust, and receive
a copy of Joshua Tickell's "From the Fryer to
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twisted


Posted by Robert Scott on November 10, 2003, 4:57 pm
 On Sun, 9 Nov 2003 20:53:06 -0500, "Mitch Dickson"

...Problem is the cost of thermocouple wire!

I made some cheap thermocouples by joining ordinary copper wire to
ordinary steel wire (like the kind you can get from a hardware store,
for arts and crafts).  You can just solder them, but if the
temperature in use is more than the melting point of solder, then you
will have to spot weld them.  (My application used only solder.)


-Robert Scott
 Ypsilanti, Michigan
(Reply through newsgroups, not by direct e-mail, as automatic reply address is
fake.)


Posted by Arjay on November 11, 2003, 3:38 pm
 
What was the voltage out of the end of the wire?  Anymore details on how
you did this or pictures?

-RJ

Posted by Robert Scott on November 11, 2003, 5:24 pm
 

The voltage was similar to what you would get from a K-type official
thermocouple.  When you pay big bucks for offical thermocouples, what
you are paying for is the precise metalurgical formulation that
produces a very precise voltage as a function of temperature.  When
you use random steel and copper wire as I did, you get a voltage that
is not so accurate.  So it would not be suitable for use in a precise
absolute temperature sensor unless you did a custom calibration of the
thermocouple against a known standard after it was constructed.

However, my application was a differential temperature sensor for a
solar collector controller.  You run copper wire from the controller
to inside the collector, change to steel which runs to some point
inside the house (for ambient), at which point it changes back to
copper to return to the controller.  As long as the metalurgy is
constant at all points except at the two transitions, it will indicate
differential temperature.  The gain may be somewhat unknown, but zero
volts will always mean equal temperatures, regardless of the
particular metalurgy.  I have no pictures, but there is really nothing
to show.  You just clean the ends of the copper and steel wires and
solder them.  Of course you have to make sure the steel doesn't short
out against some ductwork, since it does not usually come with
insulation.

-Robert Scott
 Ypsilanti, Michigan
(Reply through newsgroups, not by direct e-mail, as automatic reply address is
fake.)


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