Thermocouples can be manufactured from a diversity of metals covering a temperature range of 200 oC to 2,600 oC. Various combinations of metals i.e. calibrations exist for thermocouples.
There are approximately thirteen types of standard thermocouples available in the industry and out of them eight have been designated with an internationally known letters.
The eight designated thermocouple types are listed below:
Type K – This type of thermocouple is made up of Chromel-Alumel. It belongs to the chromium-nickel aluminum group and has a fairly linear e.m.f./temperature curve.
Type J – This type of thermocouple having limited temperature range is made up of Iron-Constantan.
Type E – It is made up of Chromel-Constantan and offers great sensitivity. It is primarily used in cryogenic i.e. low temperature range. Being a non magnetic type, it proves to be advantageous in variety of applications.
Type N – It is made up of Nicros-Nisil and offers excellent thermoelectric stability. It is extremely resistant to high temperature oxidation.
Type T – This type of thermocouple is made up of Copper-Constantan. It is found extremely useful in food, environmental and refrigeration applications.
Type S – It is made up of Platinum rhodium
Type R – It also contains Platinum rhodium and somewhat identical to type S
Type B - It is an extremely stable thermocouple made up of Platinum rhodium only. Its output is found to be very small at room temperature and offers less sensitivity in the lower range.