Thermocouple is usually and display instrument, recording instrument, computer, etc. Direct measurement of the 0 - in the process of production 1300 degrees within the scope of liquid, steam and gas medium and solid surface temperature. Thermocouple ceramic blocked pores components will be failure, often adopts the electric dust removal method to deal with, but the effect is not ideal, and cannot be used in inflammable and explosive environment, can more accurately and quickly to reflect the actual temperature of end face, is suitable for measuring temperature bearing and other parts of the face. It is not only widely used in industrial temperature measurement, and is made into standard benchmark instrument. It has matched 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. Thermoelectric emfs end temperature into a single value function relation with work. All kinds of thermocouple relationship between temperature and thermoelectric emfs indexing table are made at the cold end temperature is zero, so the use of special compensation conductor should be extended to the cold end. Working principle of thermocouple is closed loop by the two different conductor material composition, whenever there is temperature on both ends of the ladder, can produce a loop, and there will be an electric current passes through the loop, while the existed between the electrical energy on both ends, 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. Therefore, when the thermocouple temperature measurement, can be connected to the measuring instrument, measured after the thermoelectric emfs, can know the temperature of the measured medium. Thermocouple measuring temperature to the cold end ( Measure the end for the hot end, by the end of the lead connected to the measurement circuit is called cold junction) Temperature remains constant, the size of thermoelectric potential and measured temperature in certain proportion relationship. When measuring, the cold end ( Environment) Temperature changes, will seriously affect the accuracy of measurement. 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 big metal thermocouple temperature measurement area, its usage is the sum of other metal thermocouple. Thermocouple how points are negative. 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. Anode materials with ferromagnetism, can be used to distinguish between the cathode. 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.