Working principle of precious metal thermocouple!

Platinum-rhodium thermocouple is a precious metal thermocouple. 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 use temperature of this thermocouple is 1600℃, and the maximum short-term use temperature is 1800℃.

Advantages: Platinum-rhodium thermocouple has the highest accuracy, best stability, wide temperature measurement range, long service life, and high upper temperature measurement limit in the thermocouple series. It is suitable for oxidizing and inert atmospheres, and can also be used in vacuum for a short period of time, but not for reducing atmospheres or atmospheres containing metal or non-metal vapors. An obvious advantage of type B thermocouples is that they do not require compensation wires for compensation, because the thermoelectric potential is less than 3μV in the range of 0~50℃.

Disadvantages: The disadvantage of platinum-rhodium thermocouples is the thermoelectric potential, the thermoelectric potential rate is small, the sensitivity reading is low, the mechanical strength decreases at high temperature, it is very sensitive to pollution, and the precious metal materials are expensive, so the one-time investment is large.

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.

Selection of platinum-rhodium thermocouples: When the measured temperature is normally 1000~1300℃, it is recommended to use a single platinum-rhodium thermocouple (platinum-rhodium 10-platinum), and when the measured temperature is normally 1200~1600℃, it is recommended to use a double platinum-rhodium thermocouple (platinum-rhodium 30-platinum-rhodium 6), so that the service life of the platinum-rhodium thermocouple can be guaranteed within the temperature range used.