Abstract: A process control system providing a particular control effort function is divided into a primary control effort portion having a primary controller, and a feed back from the controlled process to the primary controller, and a secondary control effort portion having a secondary controller in controlling relation therewith, and receiving its control input from the primary controller. The secondary controller is provided with limits such that it becomes saturated in operation, thereby permitting selective overriding by the primary controller, while utilizing the secondary controller and actuators the maximum practical amount. The arrangement is suitable for use with continuously variable devices or for use with on-off (bang-bang) devices. The particular embodiments illustrated are (1) a bang-bang heater system, and (2) a continuously variable fluid flow control system.