Monitoring automatically controlled processes using statistical control charts

Statistical process control (SPC) and automatic process control (APC) are integrated under a hierarchical scheme. The integrated scheme is called statistical and automatic process control (SAPC). SAPC is based on the comparison of the outputs of the actual system and parallel systems that model the actual system under assumed deterministic disturbances. While APC provides a continuous controller intervention, SPC acts as a supervisory controller to detect process disturbances. A cross-correlation method is used to estimate the time when the disturbance starts to affect the system as well as the type of the disturbance. After the magnitude of the disturbance is determined, a counter action is applied on the system to minimize its effect.