Explain the purpose of cold junction compensation in thermocouples
Suppose, we are measuring a temperature of 500°c. If we use a thermocouple, the output mV of the thermocouple will be the difference between a hot junction (measuring junction) and a cold junction (reference junction). In this case, the hot junction temperature is 500°c and the cold junction temperature will be the temperature around the local transmitter or the temperature around the temperature converter in the control room that will be the room temperature or the ambient temperature which can be around 20-30°c. So basically the cold junction is not 0°. So the output mV, in this case, will be for 470°c(say cold junction temperature is 30°c) which has an error of 30°c. When we consider cold junction compensation, we use thermistors or cold junction compensation IC such as AD594 to make the cold junction temperature as 0°c so that output mV will be obtained for the exact hot junction temperature.