Thermocouple Classification Compensation Wire and Cold End Treatment
Classification and compensation of thermocouple wires
Thermocouple according to the different materials can be divided into S, R, B, K, N, E, J, T8 kinds of standardized thermocouple. The steel is often used in the S, R, B these three thermocouples.
Steelmaking materials commonly used in steelmaking
Thermocouple indexing thermode material
S-type platinum and rhodium 10-platinum
R-type platinum and rhodium 13-platinum
B-type platinum and rhodium 30-platinum and rhodium 6
In the thermocouple there is a more important material - compensation wire, with them thermocouple and measuring device connected to compensate for the thermocouple junction temperature changes generated by the error, the compensation wire should be due to the core alloy wire material different points For the extended and compensated two, we usually use the compensation type.
Zero migration method
Application areas: If the cold end is not 0 ℃, but very stable (such as the thermostat workshop or air-conditioned place).
Substantially: a constant value is added to the measurement result. Since the cold junction temperature is constant, the electromotive force EAB (TH, 0) is a constant, and the compensation is made by increasing the appropriate value by indicating the adjustment of the zero point on the instrument The Example: If the mechanical zero point of the instrument is adjusted to the scale of TH at room temperature, the temperature value indicated by the pointer is not 0 ° C but TH when the thermoelectromotive force is zero. And the cold junction temperature of the thermocouple is TH, then only when the hot end temperature T = TH, can make EAB (T, TH) = 0, so that the indication value and the actual temperature of the hot end of the same. This method is very simple, and once and for all, as long as the cold side of the temperature always remain in the TH unchanged, the indication is always correct.
Cold end compensator method
Using the unbalanced bridge to generate thermoelectric potential compensation thermocouple due to cold end temperature changes caused by changes in thermoelectric potential.
Software processing
For the computer system, do not have to rely on hardware thermocouple cold end processing. For example, if the cold junction temperature is constant but not 0 ° C, it is only necessary to add a constant corresponding to the cold junction temperature after sampling.
For the case of frequent fluctuations in T0, you can use the thermistor or other sensors to T0 signal input to the computer, according to the formula to design some programs, can automatically correct. The latter case must consider the input sampling channel in addition to the thermoelectromotive force should also have a cold junction temperature signal, if the thermocouple cold junction temperature is not the same, but also separate sampling, if the number of channels occupied too much Use the compensation wire to connect all the cold terminals to the same temperature, only a cold junction temperature sensor and a correction T0 input channel on it. Cold end concentration, for improving the speed of multi-point inspection is also very favorable.
