Thermocouple

     A temperature sensor based on the principle that a voltage is produced when two dissimilar metals. The junction produces a voltage in proportion to the difference in temperature between the measuring junction and the reference junction.Thermocouples are available in different combinations of metals or common calibrations. The four most calibrations are J, K, B and R. Each calibration has a different temperature range and environment, although the maximum temperature varies with the diameter of the wire used in the thermocouple. Some commonly used thermocouples are:

TypeK(Chromel/Alumel)thermocouple

      Type K is the 'general purpose' thermocouple. It is low cost and, owing to its popularity, it is available in a wide variety of probes. Thermocouples are available in the -200 °C to +1200 °C range. Sensitivity is approx 41 µV/°C. Use type K unless you have a good reason not to.

Mineral  Insulated  thermocouple:
Grounded,  ungrounded  and  exposed  junctons,
Material  used  :SS/Inconel sheath
Applications : Heat treating,Furnaces/kilns, Diesel engines, food processing, plastic molding Machinery, industrial processing, refrigerator temperature control, oven temp.controller, Packaging equipments.
Application temperature: upto 1200 Deg C.
Features: special mgo insulation protect thermocouple from moister, contamination and thermal Shock. Permits operation at high temperature/pressure environments. Flexibility of MI cable Allows bending & forming of the thermocouple without the risk of collapsing and cracking the Sheath.

TypeJ(Iron/Constantan)thermocouple

     Limited range (-40 to +750 °C) makes type J less popular than type K. The main application is with old equipment that can not accept 'modern' thermocouples. J types should not be used above 760 °C as an abrupt magnetic transformation will cause permanent decalibration.
     Thermocouple types B, R and S are all 'noble' metal thermocouples and exhibit similar characteristics. They are the most stable of all thermocouples, but due to their low sensitivity (approx 10 µV/°C) they are usually only used for high temperature measurement (>300 °C).

TypeB(Platinum/Rhodium)thermocouple

     Suited for high temperature measurements up to 1800 °C. Unusually type B thermocouples (due to the shape of their temperature / voltage curve) give the same output at 0 °C and 42 °C. This makes them useless below 50 °C.

TypeR(Platinum/Rhodium)thermocouple

     Suited for high temperature measurements up to 1600 °C. Low sensitivity (10 µV/°C) and high cost makes them unsuitable for general purpose use.

TypeS(Platinum/Rhodium)thermocouple

     Suited for high temperature measurements up to 1600 °C. Low sensitivity (10 µV/°C) and high cost makes them unsuitable for general purpose use. Due to its high stability type S is used as the standard of calibration for the melting point of gold (1064.43°C).