Many combinations of materials have been used to produce acceptable thermocouples, each with its own particular application spectrum. However, very few specific types are now easily available, and covering by far the majority of the temperature and environmental applications.
The standard covers the eight specified and most commonly used thermocouples. These thermocouple types can be subdivided in 3 groups, base metal, Noble (rare) metal and Refractory metal thermocouple.
Base Metal Thermocouples
Base metal thermocouple types are composed of common, inexpensive metals such as nickel, iron and copper. The thermocouple types E, J, K, N and T are among this group and are the most commonly used type of thermocouple.
Noble Metal Thermocouples
Noble metal thermocouples are manufactured with wire that is made with precious or “noble” metals like Platinum and Rhodium. The main types are R, S and B.
Refractory Metal Thermocouples
Refractory metal thermocouples are manufactured with the exotic metals tungsten and Rhenium. These metals are expensive, difficult to manufacture and wire made with these metals are very brittle.
|Thermocouple Type||Material + & -||Temperature Range ( º C)||Application|
|E||Chromel & Constantan (Ni-Cr & Cu-Ni)||-200 to 900º C||Inert media, Oxidizing media|
|J||Iron & Constantan (Fe & Cu-Ni)||0 to 750ºC||Inert media, Oxidizing media, Reducing media Vacuum|
|K||Chromel & Alumel (Ni-Cr & Ni-AI)||-200 to 1250ºC||Inert media, Oxidizing media|
|N||Nicrosil & Nisil (Ni-Cr & Ni-Si)||-270 to 1300ºC||Inert media, Oxidizing media|
|T||Copper & Constantan (Cu & Cu-Ni)||-200 to 350ºC||Inert media, Oxidizing media, Reducing media Vacuum|
|R||87% Platinum/13% Rhodium &|
(Pt & Pt-Rh)|0 to 1450ºC|Inert media, Oxidizing media.|
|S|90% Platinum/10% Rhodium &
(Pt & Pt-Rh)|0 to 1450ºC|Inert media, Oxidizing media,|
|B|70% Platinum/ 30% Rhodium & 94%
(Pt-Rh & Pt-Rh)|0 to 1700ºC|Inert media, Oxidizing media.|
|C|95% Tungsten/ 5% Rhenium & 74% Tungsten/ 26% Rhenium|0 to 2320ºC|Vacuum inert and reducing|
|G|Tungsten & 74% Tungsten/ 26% Rhenium|0 to 2320ºC|Vacuum inert and reducing|
|D|97% Tungsten 3% Rhenium & 75% Tungsten/ 25% Rhenium|0 to 2320ºC|Vacuum inert and reducing|