(1) Category of thermocouple
Common thermocouple and standard thermocouple can be divided into two major categories of non-standard thermocouple. Standard thermocouple refers to the relationship between the national standard thermoelectric power and temperature, tolerance, and a unified standard thermocouple indexing table, it has its support of the display instruments are available. Non-standardized thermocouples on the scope or magnitude and not standard thermocouple, generally there is no uniform indexing table, mainly used for the measurement of certain special occasions.
(2) thermocouple material
In theory, any two conductors can be formulated as a thermocouple, but in fact not all materials can make a thermocouple, so the hot electrode material must meet the following points:
After action by the temperature thermocouple materials can produce high thermoelectric power, thermoelectric power and the relationship between temperature preferably in the form of a single-valued function of a linear or nearly linear;
Higher temperatures can be measured and used in a wide range of internal temperature, after long-term use, physical and chemical properties and thermoelectric properties remain stable;
Material requirements for a small temperature coefficient of resistance, high resistivity, good conductivity, heat capacity is smaller;
Better reproducibility, ease of mass production and exchange, to facilitate the development of a unified indexing table; good mechanical properties, uniform material; abundant resources, cheap.
(3) In order to ensure thermocouple reliable and stable work of the thermocouple structure requirements are as follows:
① welding electrodes consisting of two hot thermocouple must be firm;
② two hot electrodes to each other should be well insulated to prevent short circuits;
③ compensation wire thermocouple is connected to the free end of the convenient and reliable;
④ protection tube should be able to ensure adequate thermal isolation electrode and harmful media.
