What does the K in a type K thermocouple mean and likewise for the rest?

Is it elemental (I don't see any potassium in there though) or something else?



closed as off-topic by Voltage Spike, Leon Heller, Daniel Grillo, Dmitry Grigoryev, Sunnyskyguy EE75 Dec 18 '16 at 3:02

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The letters are arbitrary "nicknames" for various common types. For example:

  • E = chromel–constantan
  • J = iron–constantan
  • K = chromel–alumel which is probably the most popular kind.
  • T = copper–constantan

and many others which you should have looked up in Wikipedia or some similar online source. Really, you could have found the answer to your question in much less time than it took to come here and type it in. This forum is rather averse to simple questions like yours which could have been easily researched on your own.

  • \$\begingroup\$ Arbitrary nicknames is what I thought. There's no outright source that says this. Thanks. \$\endgroup\$ – azazelspeaks Dec 13 '16 at 19:22

This is kind of an interesting question. The ASTM book Heat Resistant Materials has this to say (not sure when it was written- the copyright date is relatively recent, but it could have been written much earlier):

At present, five base-metal and three noble-metal thermocouples have been standardized and given letter designations by ANSI(American National Standards Institute), ASTM (American Society for Testing and Materials) and ISA (Instrument Society of America). Among the remaining thermocouples in use, some have not been assigned letter designations because of limited use, and some are being considered for standardization.

Often standards groups tend to codify and standardize existing practice rather than initiating completely new, say, designations, so this still leaves the question open as to why, say 'K' and what (if anything) happened to 'A', 'D' and so on.

In the case of that book, the J,K,T,N, and E base-metal and R,S,B precious-metal types were probably used before the standards agencies came along. I am personally familiar with other types (W, C, and M) which may not be completely standardized. I see references to U and L as well. Type L seems to be a variant on Iron-Constantan (J), and U a variant on Copper-Constantan (T).

You may note that the reference above is quite USA-centric. There was also a Japanese (JIS) Iron-Constantan that had a slightly different alloy (and thus different EMFs) compared to US type J. U and L seem to be more Euro-oriented (DIN 43 710), as I think N was originally.


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