A thermocouple is a sensor used to measure temperature. Thermocouples are made with two wires of different metals, joined together at one end to form a junction. The junction is placed on the surface or in the environment that's being measured. As the temperature changes, the two dissimilar metals begin to deform, causing a change in resistance. Naturally, a thermocouple outputs a millivolt signal, therefore, as the resistance changes, the change in voltage can be measured. Thermocouples are desirable because they're extremely low cost, simple to use, and are capable of providing accurate readings.
Known for their versatility as temperature sensors, thermocouples are manufactured in a variety of styles, such as thermocouple probes, thermocouple probes with connectors, transition joint thermocouple probes, infrared thermocouples, bare wire thermocouple or even just thermocouple wire.
Due to their wide range of models and technical specifications, it is extremely important to understand its basic structure, functionality, ranges as to better determine the right type and material of thermocouple for an application.
How does a thermocouple work?
When two wires composed of dissimilar metals are joined at both ends and one of the ends is heated, there is a continuous current which flows in the thermoelectric circuit. If this circuit is broken at the center, the net open circuit voltage (the Seebeck voltage) is a function of the junction temperature and the composition of the two metals. Which means that when the junction of the two metals is heated, or cooled, a voltage is produced that can be correlated back to the temperature.
Origin of Thermocouples
In 1821, Thomas Seebeck discovered the continuous current flow in the thermoelectric circuit known as THE SEEBECK EFFECT. The flow happens when two wires of dissimilar metals are joined at both ends and one of the ends is heated.