The basic principle of a thermocouple sensor is based on the Seebeck effect, which is the phenomenon where a voltage is generated at the junction of two dissimilar metals when there is a temperature gradient along the length of the metals. In simpler terms, a thermocouple consists of two wires made of different metal alloys that are joined together at one end, called the measuring junction or hot junction. The other ends of the wires are connected to a measuring instrument or a temperature controller.
When there is a temperature difference between the hot junction and the other end of the thermocouple (known as the reference or cold junction), a voltage is produced across the two junctions. This voltage is proportional to the temperature difference and the type of metals used in the thermocouple. By measuring this voltage, the temperature at the hot junction can be determined.
The thermocouple is typically calibrated to a known temperature scale (such as Celsius or Fahrenheit) to provide accurate temperature readings. It is commonly used in various industrial, commercial, and scientific applications due to its simplicity, ruggedness, and wide temperature range capabilities. Different types of thermocouples use different combinations of metal alloys, each suited for specific temperature ranges and applications.