 This overshoot can be avoided by freezing of the integral function after the opening of the door for the time the control loop typically needs to reheat the furnace.A PI controller (proportional-integral controller) is a special case of the PID controller in which the derivative (D) of the error is not used.The controller output is given by
where formula_61 is the error or deviation of actual measured value (PV) from the setpoint (SP).