Analysis of the application advantages, principles and temperature measurement range of platinum-rhodium thermocouples

Nowadays, platinum-rhodium thermocouples are still relatively widely used in the field of industrial chemical industry, especially in power plants, chemical production, high-temperature furnaces, etc., where platinum-rhodium thermocouples are almost always used as temperature measurement elements. The proportion of other types of thermocouples is very small. Large enterprises and national projects all use reliable platinum-rhodium thermocouples. The main reason is that platinum-rhodium thermocouples have many advantages.

The advantages of platinum-rhodium thermocouples are accurate measurement, good temperature performance, high temperature resistance, long service life, and it can be suitable for different oxidizing and inert atmospheres. The application range and field are extremely wide. It is used as a temperature sensing element. Generally, it needs to be used in conjunction with temperature transmitters, displays, etc. As a thermal set for temperature control, the temperature measurement range of platinum-rhodium thermocouples is very wide. It can measure gases, liquids, and solids in the range of 0~1800°, and can also be used for steam measurement.

Working principle of platinum-rhodium thermocouples:

The working principle of platinum-rhodium thermocouples is that when the two ends of two conductors of different components are connected into a loop, when the temperatures of the two junctions are different, a thermal current will be generated in the loop. If there is a temperature difference between the working end and the reference end of the thermocouple, the display instrument will indicate the temperature value corresponding to the thermoelectric potential generated by the thermocouple.

Platinum-rhodium thermocouples are divided into various models according to the different measured temperatures. When the measured temperature is normally between 1000 and 1300°C, it is recommended to use a single platinum-rhodium thermocouple (platinum-rhodium 10-platinum). If the measured temperature is normally between 1200 and 1600°C, it is recommended to use a double platinum-rhodium thermocouple (platinum-rhodium 30-platinum-rhodium 6). In this way, the service life of the platinum-rhodium thermocouple can be guaranteed within the temperature range used.

Platinum-rhodium thermocouples are precious metal thermocouples. The wire diameter is specified as 0.5mm, with an allowable deviation of -0.015mm. The nominal chemical composition of the positive electrode (BP) is a platinum-rhodium alloy, which contains 30% rhodium and 70% platinum. The negative electrode (BN) is a platinum-rhodium alloy, which contains 6% rhodium, so it is commonly known as a double platinum-rhodium thermocouple. The maximum long-term operating temperature of the thermocouple is 1600℃, and the maximum short-term operating temperature is 1800℃.