What Is A Hot Junction?

A hot junction is the measuring point on a temperature sensor, most commonly a thermocouple. It is the point where the positive and negative legs of the thermocouple wire are welded together. 

Hot junctions are created without any medium to reduce contamination, and at Peak Sensors we laser weld thermocouple hot junctions. Hot junctions can also be used to describe the point where a pt100 sensor has been attached to its leads although the measuring point on a resistance thermometer is the element itself.

Thermocouple hot junction drawing

What is the difference between a hot junction and a cold junction?

The terms “hot junction” and “cold junction” are primarily used in the context of thermocouples, which are devices used for measuring temperature. Here’s the distinction between the two:

Hot Junction:

Definition: The hot junction is the point where the two dissimilar metals of a thermocouple are joined and exposed to the temperature being measured.
Purpose: It is the sensing point of the thermocouple and is placed in the environment where the temperature needs to be measured.
Role in measurement: The temperature at the hot junction creates a thermoelectric voltage due to the Seebeck effect, which is dependent on the temperature difference between the hot junction and the cold junction.

Cold Junction:

Definition: The cold junction (also known as the reference junction) is the end of the thermocouple that is kept at a known reference temperature. It is where the thermocouple wires connect to the measuring instrument.
• Purpose: It serves as the reference point for the thermocouple measurement.
Role in measurement: The cold junction’s temperature must be known or compensated for to accurately determine the temperature at the hot junction. The overall voltage generated by the thermocouple is proportional to the temperature difference between the hot and cold junctions.

If you want to order a temperature sensor or you are unsure exactly what you need, get in touch and we can help you.

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