Thermocouples generate electricity through the Seebeck effect, which is the conversion of temperature difference into electrical voltage. This is due to the fact that the junction of two different metals creates a small voltage when there is a temperature difference between the two junctions.
The two metals used in thermocouples are typically different types of alloys, such as iron-constantan or chromel-alumel. These metals have different thermoelectric properties, which allows them to produce a voltage when there is a temperature difference between the two junctions.
Thermocouples measure temperature by detecting the voltage produced at the junction of the two metals. This voltage is then converted into a temperature reading using a reference table or equation that correlates the voltage to a specific temperature.
The range of temperatures that thermocouples can measure depends on the type of metals used and the accuracy of the instrument. Generally, they can measure temperatures from -200°C to 2000°C, with an accuracy of around ±0.5°C to ±2.5°C.
Factors such as humidity and electromagnetic interference can affect thermocouple measurements by introducing additional sources of heat and electrical noise, which can disrupt the voltage output and affect the accuracy of the temperature reading. To minimize these effects, thermocouples are often shielded and placed in environments with controlled humidity levels.