How Do Thermocouples Work

We usually use a thermometer to measure temperature. What if the temperature is so high that it will boil away the mercury in the thermometer, as can be the case with production heaters? What do we use in such situations? We use thermocouples.

Metals conduct heat as well as electricity when they are heated. The metal electrons get energized near the end of the heated metal and move away to the other end. This causes a positive charge build-up at the heated end of the metal and a negative one at the other end. Thus, current flows in the heated metal. The higher the temperature, the more the current that flows.

If two dissimilar metals of equal length are connected together in a loop then they will have different electrical and heat conductive properties. If one junction is heated and the other is held at a known temperature, then the size of the current is proportional to the amount of heat we apply at the first junction. Such a device is called a thermocouple.

If we measure a few known temperatures with this device, we can figure out the mathematical relationship between the current and the temperature. Thus, we can calibrate the thermocouple. Once the thermocouple is calibrated, it can measure any unknown temperature.

Thus, thermocouples allow us to measure temperatures in thousands of degrees Celsius, which would be impossible to measure using traditional means.

Profire Energy is a supplier of thermocouples from ThermX and Wika that are used with its PF2100 and PF3100 BMS solutions. To learn more about our products and solutions visit