Commonly used infrared elbow type thermocouple could be divided into two types: standard thermocouple and non-standard thermocouple. Standard thermocouple refers to the national standard specifies its thermoelectric potential and the relationship between temperature, permissible error, and a unified standard score table of thermocouple, it has with matching display instrument to choose from. Non-standard thermocouple or on the order of magnitude less than the range using standardized thermocouple, generally no unified indexing table, mainly used for the measurement of some special occasions. Standardized thermocouple China since January 1, 1988, thermocouple and thermal resistance were manufactured according to IEC international standard, and specify the S, B, E, K, R, J, T seven standardization thermocouple type thermocouple for China unified design.
Theoretically, any two different conductors (or semiconductor) can be made into infrared elbow type thermocouple, but as a practical temperature measurement component, is various to the requirement of it. In order to guarantee the reliability of engineering, as well as the measuring accuracy of enough, not all materials can form a thermocouple, generally electrode materials of thermocouple, basic requirements are:
1, within the scope of the temperature measurement, thermoelectric properties of stability, not change with time, there is plenty of physical and chemical stability, less susceptible to corrosion and oxidation;
2, small temperature coefficient of resistance, high electrical conductivity, specific heat;
3, large temperature of thermoelectric ShiYao, and between thermoelectric potential and temperature is linear or close to linear single valued function relation;
4, material replication is good, high mechanical strength, simple manufacturing process, the price is cheap.