The first item to discuss are the two different types of Thermocouples, types J and K. Thermocouples are two dissimilar metals that are fused together, these metals react in such a way that they emit a µV, proportional to the temperature that they are subject. Type J Thermocouples are more sensitive, providing a 50 µV/°C change, whereas Type K is 41 µV/°C. The big difference is the range of operation, Type J is somewhat limited ranging from -40°C to 750°C and type K from -200°C to 1350°C. Process temperatures to be measured dictate the type of thermocouple to utilize. Type J Thermocouples have one wire made of Iron and the other Constantan. Type K Thermocouples are made with Chromel and Alumel. Any junction of dissimilar metals will create a mini T/C “cold junction” adding to, or subtracting from, the real thermocouple signal so it is important to extend thermocouple wires with the same material, that is why the engineer will use a thermocouple terminal block – because they are made of the same thermocouple material and will not degrade the real process signal.