There are two position, three position, proportion, proportion integral, proportion integral and proportion integral differential in heat treatment temperature automatic control.

1) two position regulation - it only has two states of opening and closing, when the furnace temperature is lower than the limit given value, the actuator is fully open; when the furnace temperature is higher than the given value, the actuator is fully closed. (contactor is generally used for actuator)

2) three position regulation - it has two given values of upper and lower limits. When the furnace temperature is lower than the given value of lower limit, the entertainer is fully open; when the furnace temperature is between the given value of upper and lower limits, the actuator is partially open; when the furnace temperature is higher than the given value of upper limit, the actuator is fully closed. (for example, when the tubular heater is a heating element, three position adjustment can be used to realize the difference between heating and insulation power)

3) proportional regulation (P regulation) - the output signal (m) of the regulator is proportional to the deviation input (E). Namely:

M=ke

Where: K -- scale factor

There is a corresponding proportional relationship between the input and output of the proportional regulator at any time. Therefore, when the furnace temperature changes to reach equilibrium through proportional regulation, the deviation when the furnace temperature cannot be added to the given value is called "static difference"

4) proportional integral (PI) Regulation -- in order to "static difference", integral (I) Regulation integral is added to the proportional regulation. Regulation means that the output signal and deviation of the regulator increase with the increase of time, and there is no output signal until the deviation is eliminated, so the combination of proportional regulation and integral regulation that can eliminate "static difference" is called proportional integral regulation.