Sean Breheny wrote:
> Is there really one reference junction, though? I am under the
> impression that any joint of dis-similar metals in the thermocouple
> circuit will cause a voltage difference which is temperature
> dependent. This includes even things like bond wire connections inside
> the IC used to read the thermocouple. So, I'm not sure that it makes
> sense to couple the cold junction sensor so closely with the TC
> connector unless you are also coupling it closely with the rest of the
> electronics in the circuit which reads the TC.

Temperature differences don't matter anymore when both conductors are made
of the same material, like both become copper traces on a PC board.  For
best accuracy you want both junctions, each between one of the thermocouple
wires and the PC board, to be at the same known temperature.  The
thermocouple voltage then tells you the difference between this temperature
and the junction at the other end of the cable where the two dissimilar
conductors meet.  Add that to the known absolute temperature and you get th=
e
absolute temperature at the end of the thermocouple.



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