Unusual thermocouple types?

What are some unusual thermocouple types?

What I’m aware of are:

K, N and relatives (chromium, nickel, silicon, aluminum alloys),

T, E, and J (the constantan types),

Exotic high temperature types B, S, R, Wx (G, C, D), and other alloys of tungsten, rhodium, iridium, tantalum, and other refractory metals,

Antimony/bismuth (by far the highest signal of those listed here, used in infrared-detecting thermopiles).

No, answer, but another question. What do the letters stand for, if anything? I used to use both J- and K-type thermocouples at work, and I always wondered why they called them that.

Don’t know that the letters stand for anything. K was invented by, I think, a Hoskins company, and it uses “chromel” and “alumel”. Perhaps somebody called it “kromel” as a cutsey trade name? N is Nicrosil and Nisil, so maybe those are related - but I don’t know which got named first, the type or the alloys. E has the largest "e"lectromotive force of any of the common ones. But these are all just guesses, and I sort of doubt they’re right.

The letter designations came from the Instrument Society of America (ISA) which was later adopted as an international standard, but I have no idea how the ISA assigned them in the first place.

This doesn’t have enough detail to answer your question, but according to NIST Monograph 175,

Of the top of my head…

K, J, T, and E are the most commonly encountered base-metal thermocouple types, with K and J being the most common of these. I like type K. I think type J sucks. T is often used at cold temperatures, since it’s the only thermocouple type where limits of error have been assigned for T < 0 °C. Type T is also a good choice for thermopile (differential) setups. Type E is often used in research, since its high sensitivity can be easily read with a nanovoltmeter.

I’ve used type W thermocouples in a vacuum furnace. They’re very difficult to work with, and a real bitch to weld.

Types S, B, and R are “noble metal” thermocouples. Because they use platinum alloys they’re very expensive per inch. Type S is commonly used as an interpolation standard for calibration purposes. Type B is cool… it’s the only thermocouple type that doesn’t need a reference junction. Just hook up a nanovoltmeter and take a reading.