A cold junction (also known as a reference junction) is an essential concept in thermocouple temperature measurements. It refers to the part of the thermocouple circuit that is not exposed to the temperature being measured, typically the point where the thermocouple wires connect to the measurement device or instrumentation. This junction is at a known temperature and is crucial for accurate temperature readings.

Why is the Cold Junction Important?

When a thermocouple generates a voltage due to the temperature difference between the hot junction (where the temperature is being measured) and the cold junction, the voltage generated is directly proportional to the temperature difference between the two junctions.

Since thermocouples measure the difference in temperature between the hot junction (the measuring point) and the cold junction (the connection point), the voltage produced by the thermocouple depends on the temperature at both junctions. If the temperature at the cold junction changes, it will affect the voltage generated, leading to inaccurate readings unless corrected.