In metallurgy, the temperature of liquid steel is most often measured using thermocouples of B, S or R graduations. Abroad, S graduation thermocouples are widespread. In domestic production, B graduation is used in the overwhelming majority of cases. This graduation has a slightly higher error, but unlike S and R graduations, B graduation does not require the use of a special compensation cable. Ordinary copper wires can be used as it.

The thermocouple is a replaceable, single-use unit (or as it is also called a thermocouple package, a disposable thermocouple, PTPR-91, EVRAZTEMP, Positherm - Heraeus Electro-Nite), connected to a thermocouple (also called a rod, fishing rod, peak).

The replaceable unit consists of a cardboard sleeve and a thermocouple head, which is pressed into one end of the sleeve. The cardboard sleeve performs a protective function and, when immersed in molten metal, protects the thermocouple fittings from contact with the liquid metal and from temperature effects. In the head, under a steel (or aluminum) protective cap (which performs protective functions in the presence of slag on the surface of the melt), a sensitive element is located in a U-shaped quartz tube - the thermocouple itself. The ends of the sensitive element (a thin wire made of platinum and rhodium alloy) are welded to two copper contacts, which are attached to the polypropylene base of the head.