What is the working principle of high-temperature anti-corrosion platinum rhodium thermocouples

The widespread use of high-temperature anti-corrosion platinum rhodium thermocouples:
As one of the most widely used temperature sensors in industrial temperature measurement, thermocouples, together with platinum thermistors, account for about 60% of the total temperature sensors. Thermocouples are generally used in conjunction with visible surfaces to directly measure the surface temperature of liquids, vapors, gas media, and solids within the range of -40 to 1800 ℃ in various production processes.
Advantages of high-temperature anti-corrosion platinum rhodium thermocouples:
① High measurement accuracy; ② Wide measurement scale; ③ The structure is simple and the thermocouple is easy to use.
The basic principle of thermocouple temperature measurement
A thermocouple is a temperature sensing element that is a primary surface that directly measures temperature and converts the temperature signal into a thermoelectric electromotive force signal, which is then converted into the temperature of the measured medium through the electrical surface (secondary surface).
The basic principle of thermocouple temperature measurement is that two different materials of conductors form a closed circuit. When there is a temperature gradient at both ends, there will be current passing through the circuit. At this moment, there is an electromotive force between the two ends - thermoelectric electromotive force, which is called the Seebeck effect.
Two homogeneous conductors with different compositions are thermoelectric electrodes, with the working end at the higher temperature and the free end at the lower temperature. The free end is generally at a stable temperature. Based on the functional relationship between thermoelectric electromotive force and temperature, create a thermocouple calibration table; The graduation table is obtained under the condition of a free end temperature of 0 ℃, and different thermocouples have different graduation tables.
When a third type of metal data is connected to a thermocouple circuit, as long as the temperature of the two contacts of the data is the same, the thermoelectric potential generated by the thermocouple will remain unchanged, that is, not affected by the connection of the third type of metal to the circuit. Therefore, when measuring temperature with a thermocouple, the measuring surface can be connected, and after measuring the thermoelectric electromotive force, the temperature of the measured medium can be known.
Thermocouples weld two different types of conductors or semiconductors A and B together to form a closed loop.
When there is a temperature difference between the two attachment points 1 and 2 of conductors A and B, an electromotive force occurs between the two, forming a huge and thin current in the circuit. This phenomenon is called the thermoelectric effect. Thermocouples work by utilizing this effect.
Two conductors with different compositions (called thermocouple wires or thermoelectric electrodes) are connected at both ends to form a circuit. When the temperature at the junction is different, an electromotive force occurs in the circuit, which is called the thermoelectric effect, and this electromotive force is called the thermoelectric potential. Thermocouples use this principle for temperature measurement, and the end directly used for measuring the temperature of the medium is called the working end (also known as the measurement end), and the other end is called the cold end (also known as the compensation end); The cold end is connected to the visible surface or matching surface, and the visible surface will indicate the thermoelectric potential generated by the thermocouple.