Patent ID: 6170044
Filing Date: 2001-01-02
Classification: G05B

Abstract:
For use in a process control system, a system for maintaining data coherency between a primary process controller operable to execute process control tasks for controlling a physical process and a backup process controller operable to replace said primary process controller upon failure, wherein said primary process controller cyclically executes said process control tasks during base control cycles having a period, T, said system comprising: a tracking circuit operable to detect changed data in a main memory in said primary process controller; a data buffer for temporarily storing said changed data wherein said changed data is continuously stored in said data buffer until said data buffer is full; and data transfer circuitry for transferring said changed data in said data buffer to a backup memory in said backup process controller at least once during each base control cycle of said primary process controller together with process data within said base control cycle for executing said process control tasks, such that said transfer of changed data does not interfere with execution of said process control tasks.