Identifying a thermocouple

Next up in the riveting Thermocouple series is how to identify an unknown thermocouple as a Type K.

There are loads of videos on Youtube on this, but I didn’t find them completely conclusive. Many of them advise “checking the colours of the leads”. Surprise! There are at least six different standards for colour coding depending on where the thermocouple came from. Check out the diagram at the bottom of this page for more info.

Since the thermocouple I was looking at didn’t match any of the above, I used the following:

  1. Temperature range: Type K’s have a temperature range from -200C -> 1100C. Range good? Check.
  2. Price: How likely is it the themocouple is an expensive exotic one rather than a cheap Type K? Yeah, cheap: Check.
  3. Material: Type Ks are basically two wires of different alloys: Chromel and Alumel. Alumel is magnetic, so its very easy to see if a magnetic sticks to one of the leads and not the other. Since Alumel should be the negative lead, this also makes it really easy to check which way round to wire it! One lead is magnetic: Check.

I’m reasonably convinced its a Type K.

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