Thermocouple temperature measurement principle is _ instrument

Thermocouple is a temperature sensing element, is a kind of instrument. It directly measuring the temperature and the temperature signals into a thermocouple thermoelectric emfs, through electrical instrument ( Secondary instrument) Convert the temperature of the measured medium. Thermocouple temperature measurement is the basic principle of two kinds of different ingredients of closed loop conductor material composition, when when there is a temperature gradient at both ends, loop will have an electric current passes through, the existed between the electromotive force on both ends - — Thermoelectric emf, this is the so-called seebeck effect ( Seebeckeffect) 。 Two different components of homogeneous conductor electrode as heat, the temperature is higher for work at the end of the end, one end of the low temperature as the free end, usually free end under a 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. Access in the thermocouple loop when the third metal material, the two contacts at the same temperature as long as the material, 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 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. Thermocouple cold junction compensation calculation method: from millivolt to temperature: measure the cold end temperature and conversion for the corresponding millivolt values, millivolt values with thermocouple, the temperature conversion. From the temperature to the millivolt: measure the actual temperature and the cold end temperature and conversion for millivolt values, respectively, after subtracting the millivolt values, quick temperature value. Two kinds of different ingredients of conductor ( Called the thermocouple wire or hot electrode) Two ends synthesis loop, when two junction temperature is not at the same time, in the circuit will generate electromotive force, this kind of phenomenon called the thermoelectric effect, and the electromotive force called thermoelectric potential. Thermocouple is to use the principle of temperature measurement, which directly used for measuring the medium temperature is called at the end of the working side ( Also known as the measuring end) , on the other side called cold end ( Also known as compensation) ； The cold end connected to the display instrument or meter, digital display table will point out the thermocouple thermoelectric potential. Thermocouple is actually a kind of energy converter, it converts heat into electricity, using thermoelectric potential generated by the measuring temperature, the thermocouple thermoelectric potential, we should pay attention to the following questions: 1: thermocouple thermoelectric potential is thermocouple temperature on both ends of the work on the function of the poor, rather than the thermocouple cold end with the job, temperature difference on both ends of the function; 2: the size of the thermocouple thermoelectric potential produced by, when material is uniform thermocouple, has nothing to do with the length and diameter of thermocouple, and only at the ends of the thermocouple material composition and temperature difference;