platinum-rhodium thermocoupleAlso known as precious metal thermocouples, they are used as temperature measurement sensors and are typically paired with temperature transmitters, regulators, and display instruments to form process control systems. They are used to directly measure or control the temperature of fluids, steam, gas media, and solid surfaces within the range of 0-1800 ℃ in various production processes. Platinum rhodium thermocouple is composed of two conductors with different compositions connected at both ends to form a circuit. When the temperature of the two junction points is different, a thermal current will be generated in the circuit. If the thermocouple refers to the working end of the junction temperature difference, the instrument will display the thermoelectric potential generated by the temperature value corresponding to the thermocouple. The thermoelectric heating of a platinum rhodium thermocouple will increase with the temperature at the measuring end, and its size is only related to the thermocouple material and the temperature at both ends, the length of the thermoelectric electrode, and the independent diameter.
　　
Due to the very different requirements, the appearance of various platinum rhodium thermocouples is often the same, but their basic structure is roughly the same, usually composed of main components such as hot electrodes, insulation sleeves, protective tubes, and junction boxes. Thermocouple thermometers belong to contact temperature measuring instruments. It measures temperature based on the principle of thermoelectric effect, also known as Seebeck effect, and is a commonly used temperature measuring element in temperature measuring instruments. Connect conductors A and B of different materials into a closed loop, with one end in contact with the temperature measuring point called the measuring end (or working end) and the other end called the reference end (or free end). If the temperature t and t0 at the measuring end and the reference end are different, then the EAB (TA thermoelectric potential) generated at A and B in the circuit, t0）, This phenomenon is called the Seebeck effect, which is a thermoelectric effect. The size of EAB varies with conductor A, material, and temperature t and T0 at the second end, and this circuit is called a prototype thermocouple. In practical applications, one end of A and B are welded together as the measuring end of the thermocouple and placed at the measured temperature t, while the reference end is separated and connected to the display instrument with a wire, and the temperature t0 at the reference end junction is kept stable. The potential measured by the display instrument only varies with the measured temperature.