Why does the temperature controller of the muffle furnace heat up?

It is normal for the muffle furnace to exceed the set temperature by 15-20 degrees. During the heating process, the ammeter will drop to zero for a while and then the display will be normal. If the set temperature is too high, it will automatically cut off the current to cool down. If the temperature is lower than the set temperature, the program will automatically replenish the current to heat up. If the temperature exceeds 50 ℃, you need to pay attention. In addition, if it does not drop after being left for hours, it is possible that the place where the thermocouple is connected is about to burn. It is recommended to check it.