# Unusual thermocouple types?

**URL:** <https://boards.straightdope.com/t/unusual-thermocouple-types/254094>\
**Category:** Factual Questions\
**Created:** [July 8, 2004, 12:40pm UTC](https://boards.straightdope.com/t/unusual-thermocouple-types/254094 "2004-07-08T12:40:06Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\
**Post date:** [July 8, 2004, 12:40pm UTC](https://boards.straightdope.com/t/unusual-thermocouple-types/254094/1 "2004-07-08T12:40:06Z")

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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).

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**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\
**Post date:** [July 8, 2004, 3:51pm UTC](https://boards.straightdope.com/t/unusual-thermocouple-types/254094/2 "2004-07-08T15:51:44Z")

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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.

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**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\
**Post date:** [July 8, 2004, 4:09pm UTC](https://boards.straightdope.com/t/unusual-thermocouple-types/254094/3 "2004-07-08T16:09:12Z")

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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.

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**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\
**Post date:** [July 8, 2004, 4:42pm UTC](https://boards.straightdope.com/t/unusual-thermocouple-types/254094/4 "2004-07-08T16:42:51Z")

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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.

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**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\
**Post date:** [July 8, 2004, 6:03pm UTC](https://boards.straightdope.com/t/unusual-thermocouple-types/254094/5 "2004-07-08T18:03:18Z")

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This doesn’t have enough detail to answer your question, but according to [NIST Monograph 175](http://srdata.nist.gov/its90/introduction/intro.html),

> [@](#):
>
> The letter designations used in this database follow the recommendations of the Instrumentation, Systems, and Automation Society (ISA) and the American Society for Testing and Materials (ASTM). The practice of identifying each of the commonly used thermocouple types with a letter was originated by the ISA and adopted in 1964 as an American National Standard (C96.1) [13]. As noted in the present ASTM American National Standard [1], the letter designations actually identify the reference tables and may be applied to any thermocouple that has a temperature-voltage relationship agreeing within the tolerances specified in the standards with the values given by the table, regardless of the composition of the thermocouple. Substantial variations in composition for a given letter type do occur, particularly for types J, K, and E.

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**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\
**Post date:** [July 8, 2004, 6:18pm UTC](https://boards.straightdope.com/t/unusual-thermocouple-types/254094/6 "2004-07-08T18:18:27Z")

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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.