Thermocouples are broadly used temperature measuring instruments found in most furnaces, kilns, powerplants, and various industries. In 1821, Mr. Thomas J. Seebeck discovered that a thermocouple would generate a current in a closed circuit when one junction is at a different temperature from another. Thermocouples contains two dissimilar metals and when coupled at one end ("hot" junction ) and at other end ("cold" junction ), generate a unique microvoltage at a particular temperature.
The temperature indicator, or thermomete,r can convert this mV into degrees Centrigrade, resulting in a direct temperature reading on the indicator. This temperature reading can be transferred via remote controller, PLC, or SCADA to display in the operator control room located in another place. PID or PLC controls furnace temperature with taking feedback from thermocouple.
To deal with different specific ranges of temperature, a variety of metals are used in the manufacturing of themocouples. There are eight types of thermocouples generally used in the industries considering characteristics of the material. Each type is denoted by a letter. Please click the following link to view a chart.
Type of Thermocouple ~Material ~Temperature Range ( °C )
S type ~Pt -10% Rh Vs Pt ~0 to 1450
R type ~Pt -13% Rh Vs Pt ~0 to 1450
B type ~Pt -30% Rh Vs Pt -6% Rh ~0 to 1750
E type ~Ni -10% Cr Vs Constantan ~0 to 1000
J type ~Fe Vs Constantan ~0 to 760
K type ~Ni -10% Cr Vs Ni-5% ( Al, Si ) ~0 to 1150
N type ~Ni -14% Cr -1.5% Si Vs Ni -4.5% Si -0.1%Mg ~0 to 1150
T type ~Cu Vs Constantan ~0 to 400
Read like: Type S thermocouple is manufactured using a platinum/10% rhodium for positive arm and pure platinum for negative arm.