The principle of thermocouple temperature measurement is thermoelectric effect. In the thermocouple loop, the high temperature end is called the measuring end (or working end), and the low temperature end is called the cold end (or reference end). The reference end is usually at a constant temperature.

According to the relationship between the temperature and the electromotive force of the reference end of the thermocouple at 0 ° C, the thermocouple graduation table is made. According to GB / t16839.1-2018 / ice60584-1:2013 standard, thermocouple includes s, R, B, t, N, J, e, K, C, a and other 10 types of thermocouple.

According to GB / t30429-2013 industrial thermocouple standard, thermocouples are divided into detachable thermocouple, non detachable thermocouple and flexible cable thermocouple. Non detachable thermocouple includes armored thermocouple and solid thermocouple. Among them, the armored thermocouple is a solid whole made of metal protective sleeve, insulating material and thermocouple wire. The armored thermocouple has good sealing performance and high mechanical strength in corresponding time period. However, due to the integrity of the armored thermocouple, it is difficult to replace. Moreover, the upper limit of this temperature measurement is high (1350 ° C), and the armored thermocouple with metal protective sleeve obviously can not meet the requirements; the solid thermocouple is a new type of thermocouple developed in Japan, which is made of high-temperature alloy or stainless steel with thick wall shell, high-purity magnesium oxide as insulation material and ordinary thermocouple, and has similar characteristics with the armored thermocouple It is not suitable for this measurement. Flexible cable thermocouples are generally used for simple and fast temperature measurement; the components of detachable thermocouples can be taken out from the protective sleeve, also known as assembled thermocouples. According to the needs of users, the thermocouple assembly can be selected and assembled freely, which has the characteristics of good flexibility, simple assembly, wide temperature range, high mechanical strength and so on. The assembled thermocouple is selected to measure the temperature.

According to the temperature range of this measurement and considering the economy and measurement accuracy, the thermocouple is NiCr Nisi K thermocouple. According to GB / t2614-2010 and the needs of this temperature measurement, the diameter of NiCr Nisi thermocouple wire is 3.2mm.