Compensation principle of thermocouple
To display the temperature measured by the thermocouple in real time, a display instrument is required. There must be a wire connection from the cold end (terminal) of the thermocouple to the display instrument to form a measurement loop. Because the wire material used is different from the electrode material of the thermocouple. According to the law of the middle metal, as long as the temperature at both ends of the connecting wire is the same, the total electric potential in the loop will not be affected after the two ends are connected to other metal materials. Therefore, the thermoelectric heat generated by the thermocouple circuit can be measured according to the law of intermediate metal.
Compensation method of thermocouple
The compensation method uses compensation wire and cold junction compensation. Compensation conductors are divided into compensating conductors and extended compensating conductors, and cold junction compensation can be used for ice slot and room temperature compensation. In the industrial production process, thermocouples usually use the compensation wire method. The advantages of using the compensation wire method; economy, low cost, realizing measurement, not only can provide the physical and mechanical properties of the measurement loop, convenient wiring, can adjust the impedance of the loop, shield static electricity and enhance anti-interference.
It is more common to use extended compensation wires in industrial production sites, and their naming is the same as the corresponding thermocouple, and the nominal value of the thermoelectric potential produced by the compensation wire of the same temperature is the same as that of the corresponding thermocouple. It is usually represented by the parent-child X, and the parent-child X represents that the material of the extended compensation wire is the same as the material of the thermocouple electrode.
For example, KX represents the compensation wire of the K-type thermocouple, and the K-type thermocouple is also a nickel-chromium-nickel-silicon thermocouple. Then the positive electrode material of the compensation wire is nickel-chromium alloy, and the negative electrode material of the compensation wire is nickel-silicon alloy. During use, the positive pole of the compensation wire uses a red insulating layer. Regardless of the positive pole of the thermocouple compensation wire, the red one is basically the positive pole of the compensation wire.