Thermocouples are temperature sensors formed by joining two materials producing different potential (mV) that is function of the difference of temperature between the end of measurement (called hot junction) and the other end (cold junction) according to the Seebeck effect.
Normalised thermocouples types vary according to the metal used. In addition the temperature of work and response in mV is different according to the type of thermocouple.
The most frequent ones are:
| Type | Materials | Field of measurement |
| Thermocouple type T | Copper/ Constantan | -250 to 260ºC |
| Thermocouple type J | Iron / Constantan | -210 to 1200 ºC |
| Thermocouple type K | Cromel/alumel | -200 to 1372ºC |
| Thermocouple type E | Cromel/Constantan | -250 to 1000ºC |
| Thermocouple type R | Pt/Rh (13%) | -50 to 1768ºC |
| Thermocouple type S | Pt/Rh(10%) | -50 to 1768ºC |
| Thermocouple type N | Ni-Cr-Si/Ni-Si | -240 to 1300ºC |
| Thermocouple type B | Pt/Rh | 400 to 1820ºC |
| Thermocouple type U | Cu/CuNi | -200 to 650ºC |
Temperature probes, beyond the type of sensor, are also affected by all constructive elements that vary depending on the application and working temperature.
Inmersor. Includes the area where the measuring element is housed, it is a bulb of a length and a certain diameter. The construction materials are usually metals: different types of stainless steels, Inconel, Hastelloy, monel, etc.
The inner isolation can be ceramic, magnesium oxide, or “encamisadas” that can support high vibrations and temperatures thanks to the compact isolation.
Head. Defines the electrical connection area. It can be a head of different shapes and standards (Din B, DIN, Cl, guaB, etc.), a connector or direct cable output.
The heads can also accommodate an electronic amplifier (transmitter or micro-converter) with configurable temperature range and different types of output signal (4-20 mA, HART, data bus, etc.)
Process connection. Define the way fixing the process. They can be threaded connections (1/4 “, ½” type GAS, BSP or NPT, DIN flanges, non-standard flanges, connections Bayonet, etc.)