Thermocouples made really easy

nekomatic said:

Nice explanation Ron, thanks.

The only thing I can think of to add is that all this relates to the temperature *of the thermocouple junction*. How close that temperature is to the temperature that you *actually want to measure or control* involves a whole lot more assumptions and possible sources of error. In almost anything other than a well stirred liquid, there are almost certain to be temperature gradients due to heat flow, including heat flow along the probe itself...

Click to expand...

Thanks and yes, that pretty much sums things up. Years ago the vacuum of work sucked me more and deeper into temperature than I ever wanted to go. Long before many of today's reference standards for temperature existed.

You make a very good point as to what I called a thermal bath, typically filled with an oil similar to automotive anti freeze. The bath could be set between -20 F. and I think 400 F. The test thermocouples were bundled with a PRT Standard and placed in the bath. The bath had a circulation pump to eliminate any thermal layers. The output voltages of the thermocouples under test were measured and recorded over a range of cardinal points. There was more to it but that's it in a nutshell. Temperatures above the bath limits were done in a small furnace which we typically did up to around 2,000 F. (Thermocouples used in large furnaces for uniformity test). Temperature measurement can really get into some interesting stuff.

Ron