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Geez! Try to omit one minor detail and the Lancair Mail List guys catch you
every time! I actually though about including this nuance last night and
said to myself "Naw, nobody's gonna call me on this one." More fool, me.
Brent is absolutely correct. In principle, one could use any connector in a
thermocouple line. If there were a transition from thermocouple wire to
another metal at the connector (like from a chromel wire to a gold-plated
pin) and a corresponding junction back to the original thermocouple material
(like from the gold plated socket to a chromel wire) and both of these
transitions were at the same temperature (almost certainly the case with a
connector) then there would not be an erroneous reading. The potential
generated in the transition from chromel to gold is balanced by an opposite
potential in the transition from gold back to chromel, and this opposite
potential is equal if both transitions are at the same temperature (which is
quite likely since the pin is stuck into the socket).
But using the thermocouple connector is good practice. Besides, ain't nobody
gonna put 12 volts into a thermocouple connector thinking it's an intercom
power cable or something.
By the way, you MUST have the thermocouple wire go all the way to the
electronic box (or more accurately, now that I know it's required, to the
temperature-compensated thermocouple amplifier that is undoubtedly contained
therein) OR ensure that the connector is at the same temperature as the
thermocouple amplifier (which would be very hard to do in practice). If you
insist on using a non-thermocouple connector (shame on you!) then don't run
copper wires from the connector to the electronic box.
Do what you will. This is a non-safety item. Me, I'd use the thermocouple
connector.
- Rob Wolf
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LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
LML Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
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