INSIGHT - Comments

Vol. 4 No. 7 - What you should know but don’t

or

How does a thermocouple work?

Dear Dr. Jennings:

I think the hidden message in this INSIGHT is that when one uses a type "T" thermocouple, one must always be sure to hook up the copper wire to the positive terminal of the datalogger.

Louis M Glasgow - August 2001

E-Mail address: lglasgow@frontiernet.net

Response by T.A. Jennings, Ph.D.

In a sense what you say is true but there is even a more subtle point that was being made. If you have a freeze-dryer,  you will note that the copper connections of the thermocouples in the dryer often become corroded with an oxide. That oxide will now change the work function of the contact. The copper-copper contact is a part of the measuring circuit and thus there will be an error in the output signal. I have seen an error of as much as 2 ^oC because of corroded contacts. So the message here is to keep the copper contacts of the thermocouples free of any corrosion or deposit.

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