Unusual thermocouple types?

Factual Questions
1

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).

2

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.

3

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.

4

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.

5

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

6

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.