The polarity of the thermocouple and extension wire is reversed

The temperature displayed by the secondary gauge is on the low side

At this time, it may be high or low, depending on the temperature at the cold end of the thermocouple and the input terminal of the instrument. If the cold-end temperature is high, the displayed temperature will be low ； If the cold forging temperature is low, the displayed temperature will be high. Well, I’m making up tongue twisters.

I agree with the answer from floor 3; another possibility is that the temperatures are equal, that is, the temperature at the cold end of the thermocouple is equal to the temperature at the wiring terminal of the instrument. In fact, it’s simple to understand this by simply applying the formula for the thermoelectromotive force generated by the thermocouple.

The analysis on the third floor makes sense. . . .

Does it matter whether it’s too big or too small? In any case, the wiring must be done accurately

The third floor is right. . . . When the temperature at the measurement point is high, the measured value becomes lower; when the temperature at the measurement point is low, the measured value becomes higher:hug:

　　The compensation wires for thermocouples are a pair of insulated wires that maintain the same nominal value of thermoelectromotive force as the thermocouple they are connected to, over a certain temperature range (including room temperature of 0). They are used to connect the thermocouple to the measuring device, thereby compensating for errors caused by temperature changes at the points where they are connected to the thermocouple. 　 　　In other words, the compensation wire can also generate a thermoelectric potential, whose magnitude is equal to the temperature difference potential between the thermocouple and the measuring device. When used correctly, with the temperatures at the cold and hot ends remaining constant, as the temperature at the junction where the thermocouple is connected to the compensation wire changes, the thermoelectric potential of the thermocouple increases while that of the compensation wire decreases, and vice versa; this helps to compensate for the effects caused by temperature changes between the thermocouple and the measuring device. The measuring device detects the superimposed potential resulting from the thermoelectric potential generated by the thermocouple and the compensation potential generated by the compensation wire. 　 　　When the temperature at the connection point between the thermocouple and the compensation wire is higher than the temperature in the control room, the compensation potential of the compensation wire is positive. It should be the thermoelectric potential generated by the thermocouple 【plus】 the compensation potential generated by the compensation wire; if they are connected in reverse, a negative value is added, which results in a lower reading ； 　　When the temperature at the junction where the thermocouple is connected to the compensation wire is lower than the temperature in the control room, the compensation potential of the compensation wire is negative. The thermoelectric potential generated by the thermocouple should be [subtracted] from the compensation potential generated by the compensation wire; if this order is reversed, subtracting a negative value will result in an overestimated reading ； 　　When the temperature at the junction where the thermocouple is connected to the compensation wire is equal to the temperature in the control room, the compensation potential of the compensation wire is zero, having no effect on the measurement