Thermocouples are by far the most common of all temperature sensor types, and are popular for their simplicity, ease of use, and speed of response to temperature changes, also its advantage of small body size. Thermocouples have the widest working temperature range among all types temperature sensor. From minus -200'C to well above 2000'C.

Thermocouples are pyroelectric sensors that basically consist of two junctions of dissimilar metals such as copper and constantan that are soldered or crimped together to make a responsible circuit to temperature . One junction is kept at a constant temperature and is called the reference junction or cold junction , while the other is the measurement junction or hot junction. When the two junctions are at different temperatures, a voltage is developed across the junctions,with reliable material and crafts the voltage vs temperature curve is predicable and hence can be used to measure temperature of working subjects.

The working principle of a thermocouple is very simple and basic. When fused together, the junction of two dissimilar metals, such as copper and constantan, creates a "thermoelectric" effect, creating a constant potential difference between them of only a few millivolts (mV). The voltage difference between the two junctions is called the "Seebeck effect" because a temperature gradient is created along the wire, which creates an electromotive force. Then the output voltage of the thermocouple is a function of temperature change.

Thermocouples can be made from a variety of different materials and can measure extreme temperatures between -200'C to +2000 Deg C. With so many choices of materials and temperature ranges, internationally recognized standards have been developed, with thermocouple color codes, allowing users to select the suitable thermocouple sensor for specific application.