What does cold-junction compensation do in thermocouple measurements?

• A. It accounts for the EMF produced by the thermocouple due to nonzero reference junction temperature.
• B. It eliminates all thermoelectric EMF entirely.
• C. It converts the thermocouple voltage to a current.
• D. It compensates for sensor drift due to aging.

Answer: (A)

Cold-junction compensation addresses the fact that the reference junction isn’t at 0°C. A thermocouple produces a voltage based on the temperature difference between its hot junction and the reference junction. If the reference is at a nonzero temperature, that temperature also contributes an EMF. Cold-junction compensation measures or estimates the reference temperature and generates an adjustment that represents the EMF the thermocouple would produce with the reference at 0°C. Adding this compensation to the measured voltage lets you relate the signal to the actual hot-junction temperature using standard tables or equations. It doesn’t remove the EMF entirely, it just accounts for the reference temp; it doesn’t convert voltage to current, and it doesn’t fix sensor aging.