MI thermocouples offer flexibility, high-temperature resistance, fast thermal response time, and durability. Like industrial prefabricated thermocouples, they are used as temperature sensors in conjunction with display instruments, recording instruments, and electronic regulators. They can also serve as the sensing element of prefabricated thermocouples, directly measuring the temperature of liquids, steam, and gases, as well as solid surfaces, in various production processes.

The working principle of a sheathed thermocouple is to weld two conductors of different compositions together to form a circuit. The end directly measuring temperature is called the measuring junction, and the connection end is called the reference junction. When a temperature difference exists between the measuring and reference junctions, a thermoelectric current is generated in the circuit. When connected to a display instrument, the instrument will indicate the temperature corresponding to the thermoelectric potential generated by the thermocouple.

The thermoelectric potential of a sheathed thermocouple increases as the temperature at the measuring end rises. The magnitude of this potential depends solely on the sheathed thermocouple conductor material and the temperature difference between the two ends, and is unrelated to the length or diameter of the thermocouple. Sheathed thermocouples are constructed by repeatedly drawing the conductor, insulating magnesium oxide, and a stainless steel protective tube. The basic structure of an sheathed thermocouple consists of a junction box, terminal blocks, and the sheathed thermocouple, along with various mounting fixtures.