What is the working principle of thermocouple thermometer _ instrument

Working principle of thermocouple thermometer of two different conductor loop, the loop will produce electric potential, the potential size is directly related to the difference in temperature between the two contact, this kind of phenomenon called the thermoelectric effect. Using thermal element is the thermocouple made of thermoelectric effect, using thermocouple as the temperature sensing element of thermometer is a thermocouple thermometer. In classical electron theory, thermoelectric potential by the temperature difference of electric potential and contact potential. Electric potential difference in temperature is caused by the inhomogeneous temperature difference on both ends of the conductors. Contact potential is when contact with the two different conductor A and B, because of the free electron density, electron diffusion at contact, the formation of the electric potential. Contact potential is not only a function of temperature t, its contribution to the thermoelectric potential also far bigger than the thermoelectric potential. Measure the thermoelectric potential thermocouple for temperature changes, according to the function relation between thermoelectric potential and temperature change can know cause temperature of thermoelectric potential. What is cold junction compensation of thermocouple thermoelectric potential temperature depends on its two ends, only when the cold end temperature constant, the output of the thermoelectric potential is measured side ( Hot side) The single value function of temperature. And engineering technology is widely used on thermocouple indexing table and according to the indexing table score of the scale of temperature display is according to the cold end temperature of 0 ° C. So, for it must compensate the cold end temperature of the thermocouple measurement accuracy can be assured. A lot of thermocouple cold junction compensation method. In industrial instrumentation and production field, the regular compensation method with cold junction compensation method and compensation bridge method. More advanced compensation methods, such as the intelligent compensation method. Such a smooth, thermocouple temperature compensation principle and method can easily understand a few common questions about cold junction compensation: 1, the compensating conductor temperature compensation of temperature measuring element connection with the difference between the control room temperature; 2, compensation circuit compensation control room temperature and need fixed theory of cold end temperature difference; 3, thermocouple and compensating conductor with the consequences. For example: when the temperature of the thermocouple with compensation cable joint is higher than the control room temperature, the potential for the compensation of the compensating conductor are, should add compensation wire is produced by the thermocouple thermoelectric potential compensation of electric potential, meet the equivalent to add a negative will make instructions is low; When the thermocouple with compensation cable joint temperature is lower than the control room temperature, the potential is negative, the compensation of the compensating conductor should be produced by the thermocouple thermoelectric potential minus wires produced by electric potential compensation, meet the equivalent of subtracting a negative will make the instruction on the high side; When the temperature of the thermocouple with compensation cable joint is equal to the control room temperature, the compensation of the compensating conductor electric potential is zero, affect the measurement ( Is the display room temperature) 。 Thermocouple temperature transmitter or card, temperature compensation circuit. Its effect is according to the law of thermocouple temperature middle - 'two contact thermocouple loop ( Temperature T, T0) Between thermoelectric potential, equal to the thermocouple in the thermoelectric potential when temperature T, Tn and when the temperature of Tn, T0 algebra and thermoelectric potential. Tn say middle temperature '. In the thermocouple cold junction temperature to produce a temperature for Tn, T0 thermoelectric potential. To uncertainty of thermocouple cold junction compensation. It is, in essence, can produce a changes over reference end temperature of dc millivolt signal. It is concatenated in the thermocouple temperature measurement circuit, the can be compensated automatically make reference end temperature. Using the root cause of the thermocouple cold junction compensation circuit, lies in the uncertainty of the cold end temperature. Although the thermocouple dividing standard is zero as a benchmark; Although normally with the cold end is zero as the benchmark to explain the principle of temperature compensation. But in fact, if the cold end temperature can be fixed, it only need to calculate the T ( T,To) And T ( T, Tn) The difference between man-made in the process of instruction a opposite error, to offset the cold end temperature is not zero will bring the error. You can get the correct measurements. So cold junction compensation circuit in temperature compensation, not necessarily to zero as the benchmark. At the same time, the thermocouple cold junction compensation circuit tend to have a adapt to the range, beyond this range will not be able to meet the requirements of the compensation.