DUAL LOOP PID CONFIGURATION

The proportional-integral-derivative controller produces a process control signal in response to a process variable signal and a setpoint signal. The process variable signal is subtracted from the setpoint signal to produce a difference signal, and a signal representative of the derivative of the process variable is produced. In an inner loop the setpoint signal, the difference signal and the derivative signal are amplified by respective adjustable gains. In an outer loop the process variable signal and the derivative signal are amplified by respective adjustable gains and the difference signal is integrated. The amplified and integrated signals are combined and applied to another adjustable gain to produce an outer-loop output signal. The amplified setpoint, difference and derivative signals, and the outer-loop output signal are finally combined to produce the process control signal. The gains of the inner loop affect the input/output characteristics of the controller and the gains of the outer loop the sensitivity of the controller to perturbations. Also, adjustment of the sensitivity through the gains of the outer loop does not change the input/output characteristics of the controller that have been previously adjusted by means of the gains of the inner loop after having set the gains of the outer loop equal to zero.