Working principle of thermocouple thermocouple is closed loop by the two different conductor material composition, when both ends exist when the temperature of the ladder, can produce a loop, and there will be an electric current passes through the loop, and then between both ends there is electricity, and that this power is called thermoelectric emf, this is called the seebeck effect, seebeckeffect) 。 Two kinds of different materials for heat conductor electrode, and here, if the temperature is high, the normal work of the end for end, on the contrary, the other end of the low temperature is the free end, usually under the condition of free end, he is under a state of constant temperature. According to the thermoelectric emf as a function of temperature, the thermocouple indexing table; Indexing table is free end temperature at 0 ℃, under the condition of different thermocouples with different indexing table. The thermocouple of the whole circuit, if access to a third metal materials, and the material when the temperature of the two contacts, produced by the thermocouple thermoelectric is set to remain the same, which is not affected by the third metal access in the loop. Take action at the cold end compensation due to the impact of the cold end temperature change is called the thermocouple cold junction compensation is normal. Connected to the measuring instrument with special compensation conductor. K type thermocouple is above 500 ℃ of dosage of large metal thermocouple temperature measurement area, its usage is the sum of other metal thermocouple. First of all we are to understand what is negative. The anode ( kp) In the name of the chemical composition is: ni: cr material 90:10, the cathode ( kn) The chemical composition of the is: ni: si material 97. K type thermocouple linearity, thermoelectric emfs is bigger, so can be used for oxidizing, inert atmosphere. But k type thermocouple cannot be directly used for sulfur, reducing or at high temperature reduction, oxidation atmosphere and vacuum alternately, is also not recommended for people with weak oxidizing atmosphere. It is very nickel-chromium alloy (containing 10% chromium kp) , the negative is extremely containing silicon 3% nickel silicon alloy ( kn) 。 Therefore, thermocouple how points are negative? Based on this feature, use the magnet can be easily identified thermocouple of positive and negative pole.