How to choose platinum rhodium 6 - Platinum rhodium thermocouple? This kind of thermocouple is 60 s up a kind of typical high temperature thermocouple. It is very containing 30% of rhodium platinum rhodium ( 英国石油公司(BP) Negative extremely 6% containing rhodium platinum rhodium ( BN） 。 Because the poles are platinum rhodium called double platinum rhodium thermocouple.
B type thermocouple is suitable for use in the oxidizing atmosphere or neutral, short-term use can also be in a vacuum environment, even in resilience atmosphere is applied, the life also is R, S type thermocouple 10 to 20 times. Because of R and S type thermocouple at low temperatures, will appear the positive to the negative dispersion of platinum, rhodium, trigger a thermocouple degradation, in order to avoid the occurrence of the above picture, add in the platinum rhodium platinum rhodium, not only can improve the function of heat resistance, and advances in platinum alloy is rate of the thermoelectric emfs. When the rhodium content below 20%, platinum rhodium thermoelectric emfs shock of platinum, but beyond this value, along with the growth of the rhodium content, little change, and the apparent hardening, processing difficult. So the rhodium content in this kind of alloy can not exceed 40% ( Weight ratio) 。
B type thermocouple is characterized by: minimal thermoelectric emfs (at room temperature 25 ℃ to - 2 mu V, 50 ℃ for 3 mu V) When measuring so common, it's not necessary to compensation conductor should be able to neglect with reference to the influence of the temperature change. Its temporary using temperature is 1600 ℃, short-term using temperature is 1800 ℃. Platinum rhodium alloy melting point is 1820 ℃, 6 shackles used temperature limit. Double platinum rhodium thermocouple electromotive force rate is small, it need to display instrument equipped with high sensitivity.
platinum rhodium is smaller than pure platinum tendency of grain length, and along with the increase of rhodium content is less, and can make the pyroelectric function more stable, higher mechanical strength. Therefore, double platinum rhodium thermocouple in 1800 ℃ low temperature measurement widely used.