Universal scheme of input/output redundancy in a process control system

Abstract

A controller of a control system, which operates as a master, has a slave input/output processor (IOP) connected thereto which communicates with at least one device of a predetermined type, and a backup slave IOP connected thereto of the same type as the slave IOP, the slave IOP operating as a primary IOP to the device. A method for providing backup to the slave IOP by the backup slave IOP comprises the steps of loading the backup slave IOP with the same data base as the slave IOP. The backup slave IOP eavesdrops on all communications from the controller to the slave IOP. When a write command is communicated to the slave IOP, the backup slave IOP taps the data from the bus and updates its data base. If the command is not a write command, ignores the communication. When a fault is detected by either the slave IOP or the backup slave IOP, the detection of the fault is communicated to the other IOP. The IOPs then failover such that the backup IOP is operatively connected to the device and the slave IOP is disconnected from the device. Finally, the controller acknowledges that the backup slave IOP is now operating as the primary source to the device.