What is cold junction compensation in thermocouple measurement?

Cold junction compensation (CJC) corrects for the temperature at the reference junction (where thermocouple wires connect to measuring instrument). Since thermocouples measure temperature difference between hot and cold junctions, if cold junction is not at 0 degrees C (ice point), compensation is needed. CJC uses an RTD or thermistor at the terminal block to measure actual cold junction temperature, and the instrument adds this correction electronically to display true process temperature.