What is thermocouple?A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference. When two wires composed of dissimilar metals are joined at both ends and one of the ends is heated, there is a continuous current which flows in the thermoelectric circuit (the thermoelectric effect or Seebeck effect).Need for reference junction( cold junction):In thermocouples, voltage is developed due to flow of electric current. This current flow depends upon the difference in temperatures at the two ends of conducting wire. That is thermocouples always measure difference in temperatures and not absolute temperature.To measure the temperature of one junction, the other junction is kept at some reference temperature. As this is done by using ice bath, it is normally called at cold junction.Using ice bath for constant temperature is useful for laboratory calibration, but is not convenient for most measurement and control applications. Instead of ice bath, an effect of cold junction is added using a thermally sensitive device such as a thermistor or diode. This is also called as isothermal block. Special care is taken to minimize any tempera...
