(s thermocouple) platinum rhodium 10- platinum thermocouple
Platinum-rhodium 10- platinum thermocouple (S-type thermocouple) is a kind of precious metal thermocouple. Even wire diameter is 0.5mm, and the allowable deviation is-0.015 mm. The nominal chemical composition of positive electrode (SP) is platinum-rhodium alloy, in which rhodium is 10%, platinum is 90%, and negative electrode (SN) is pure platinum, so it is commonly known as single platinum-rhodium thermocouple. The long-term maximum working temperature of thermocouple is 1300℃, and the short-term maximum working temperature is 1600℃.
S-type thermocouple has the advantages of highest accuracy, best stability, wide temperature range and long service life in thermocouple series. It has good physical and chemical properties, thermoelectric potential stability and high temperature oxidation resistance, and is suitable for oxidizing and inert atmosphere. S-type thermocouple, which meets the international temperature standard, has been used as an interpolation instrument for international temperature standard for a long time because of its excellent comprehensive performance. Although it is stipulated that "ITS-90" cannot be used as an internal inspection instrument for international temperature standards in the future, CCT thinks that S-type thermocouple can still be used to approximate international temperature standards.
The disadvantages of S-type thermocouple are thermoelectric potential, low thermoelectric potential rate, low sensitive reading, low mechanical strength at high temperature, very sensitive to pollution, and expensive precious metal materials, so the one-time investment is large.
(R thermocouple) platinum rhodium 13- platinum thermocouple
Platinum-rhodium 13- platinum thermocouple (R thermocouple) is a kind of precious metal thermocouple. The diameter of the dipole wire is specified to be 0.5mm, and the allowable deviation is-0.015 mm. The nominal chemical composition of the positive electrode (RP) is platinum-rhodium alloy, in which the rhodium content is 13%, the platinum content is 87%, and the negative electrode (RN) is pure platinum. The maximum long-term service temperature is 1300℃, and the maximum short-term service temperature is 1300℃.
R-type thermocouple has the advantages of the highest accuracy, the best stability, wide temperature range and long service life in thermocouple series. It has good physical and chemical properties, good thermoelectric potential stability and oxidation resistance at high temperature, and is suitable for oxidizing and inert atmosphere. Because the comprehensive performance of R-type thermocouple is equivalent to that of S-type thermocouple, it has been difficult to popularize in China, and it is rarely used in China except for measuring temperature on imported equipment. During the period of 1967- 197 1, three research institutions in Britain, NBS in America and NRC in Canada conducted cooperative research. The results show that the stability and reproducibility of R-type thermocouple are better than that of S-type thermocouple, and this research has not been carried out in China at present.
The disadvantages of R thermocouple are thermoelectric potential, low thermoelectric potential rate, low sensitive reading, low mechanical strength at high temperature, very sensitive to pollution, and expensive precious metal materials, so the one-time investment is large.
(Type B thermocouple) Platinum Rhodium 30- Platinum Rhodium 6 thermocouple
Platinum rhodium 30- platinum rhodium 6 thermocouple (type B thermocouple) is a kind of precious metal thermocouple. The diameter of even-numbered wire is specified to be 0.5mm, and the allowable deviation is-0.015 mm. The nominal chemical composition of its positive electrode (BP) is platinum-rhodium alloy, in which the rhodium content is 30%, the platinum content is 70%, and the negative electrode (BN) is platinum-rhodium alloy, and the rhodium content is 6%, so it is commonly known as double platinum-rhodium thermocouple. The long-term maximum working temperature of thermocouple is 1600℃, and the short-term maximum working temperature is 1800℃.
Type B thermocouple has the advantages of the highest accuracy, the best stability, wide temperature range, long service life and high upper limit of temperature measurement. It is suitable for oxidizing and inert atmosphere, and can also be used in vacuum for a short time, but it is not suitable for reducing atmosphere or atmosphere containing metal or nonmetal vapor. An obvious advantage of type B thermocouple is that it does not need compensation line, because the thermal potential is less than 3μV in the range of 0~50℃.
The disadvantages of type B thermocouple are thermoelectric potential, low thermoelectric potential rate, low sensitive reading, low mechanical strength at high temperature, very sensitive to pollution, and expensive precious metal materials, so the one-time investment is large.