Hierarchical-structure plant control system

Abstract From the Canadian patent

Sub-loop controllers arranged around a microprocessor are assigned to operation terminals to be controlled, and connected to a master controller and a host computer through a system bus to be supplied with a control command therefrom. Analog memories for manual control of the operation terminals are connected to the host computer through a special common wiring. If one of the sub-loop controllers breaks down, the host computer directly controls the operation terminal by use of this analog memory thereby to back up the sub-loop controller.