Also called high temperature thermocouple, precious metals platinum rhodium have single platinum rhodium (10 - platinum rhodium platinum rhodium) and double platinum rhodium (30 - platinum rhodium platinum rhodium 6), as temperature measurement sensor, usually with temperature transmitter, controller and display instrument, such as process control system, to directly measure or control in the production of a variety of fluid over a range of 0-1800 ℃, steam and gas medium and solid surface temperature.
Platinum rhodium thermocouple for precious metal thermocouple. The nominal chemical composition of the positive electrode is platinum-rhodium alloy, which contains 30% rhodium, 70% platinum, minus extremely platinum rhodium alloy, and 6% content rhodium. Therefore, it is commonly known as double platinum-rhodium thermocouple. The thermocouple long-term maximum temperature of 1600 ℃, the highest short-term using temperature is 1800 ℃.
Pt-rh thermocouple has the highest accuracy, best stability, wide temperature range, long service life and high temperature limit in thermocouple series. Suitable for oxidizing and inert atmospheres or for short-term use in a vacuum, but not for reducing atmospheres or atmospheres containing metallic or non-metallic vapors. B type thermocouple is an obvious advantage don't need a compensation for the compensation conductor, because in the range of 0 ~ 50 ℃ and internal potential less than 3 mu V.
Disadvantages: the disadvantages of platinum and rhodium thermocouple are thermoelectric potential, low thermoelectric potential rate, low sensitivity reading, low mechanical strength under high temperature, very sensitive to pollution, precious metal materials are expensive, thus large one-time investment.
The principle of pt-rh thermocouple is that the pt-rh thermocouple is composed of two conductors of different components. When the temperature of the two joints is different, the thermal current will be generated in the circuit. If there is a temperature difference between the working end and the reference end of the thermocouple, the display meter will indicate the corresponding temperature value of the thermoelectric potential generated by the thermocouple.
Platinum rhodium thermocouple choice: measurement of temperature during 1000 ~ 1300 ℃ normally recommended single platinum-rhodium thermocouple (10 - platinum platinum rhodium), measuring the temperature of the normal during 1200 ~ 1600 ℃ suggest using double platinum rhodium thermocouple (30 - platinum rhodium platinum rhodium 6), so you use temperature range to ensure the service life of platinum-rhodium thermocouple.
