Statistical and automatic control of a process under a ramp input disturbance

The existence of a typical industrial controller, e.g. a PI controller, in a closed-loop process environment generally does not guarantee that the system output is kept at the target level under all types of disturbances. While the controller takes care of the disturbance up to a certain degree, monitoring the output using statistical process control tools, such as control charts, gives additional insight on the status of the system. Consequently, the type and magnitude as well as the onset time of the disturbance can be estimated, and a counter action can be applied as shown in the SAPC methodology.