TYPE of THERMOCOUPLE
The type E thermocouple is suitable for use at temperatures up to 1650oF (900oC) in a vacuum, inert, mildly oxidizing or reducing atmosphere. At cryogeenic temperatures, the thermocouple is not subject to corrosion. This thermocouple has the highest EMF output per degree of all commonly used thermocouples.
The type J may be used, exposed or unexposed, where there is a dificiency of free oxygen. For cleanlines and longer life, a protecting tube is recommended. Since JP (iron) wire will oxidize rapidly at temperatures over 1000F (5400C), it is recommended that larger gauge wires be used to compensate. Maximum recommended operating temperature is 1400oC (760oC).
Due to its reliability and acuracy, Type K is used extensively at tempeatures up to 2300oF (1260oC). It's goog practice to protect this type of thermocouple with a suitable metal or ceramic protecting tube, especially in reducing atmostpheres. In oxidizing atmostphere, such as electric furnaces, tube protection is not always nessesary when other condition are suitable; however, it is recommended for cleanlines and general mechanical protection. Type K will generally outlast Type J because JP (iron) wire rapididly oxidizes, especially at higher temperatures.
This nikel-based thermocouple alloy is used primaily at high temperatures up to 2300o (1260oC). While not a direct replacement for Type K, Type N provides better resistance to oxidation at high temperature and longer life in application where sulfur is present. It also outperforms Type K in K's aging range.
This thermocouple can be used in either oxidising or reducing atmospheres, though for longer life, a protecting tube is recommended. Because of its stability at lower temperatures, this is a superior thermocouple for q wide variety of applications in low and cryogenic temperatures. It's recommended operating range is -330o to 660oF (-200o to 350oC), but it can be used to -425oF (-269oC) (boiling helium).
Type S, R, and B
Maximum recommended operating temperature for Type S or R is 2640oF (1450oC); Type B is recommended for use at high as 3100oF (1700oC). These thermocouple are easily contaminated. Reducing atmospheres are particularly damaging to the calibaration. Noble metal thermocouples should always be protected with a gas-tight ceramic tube, a secondary tube of porcelain, and a silicon carbide or metal outer tube as condition require.