Fault-Tolerant soft PLC control using shadow processes

This paper deals with an efficient and fault-tolerant control system for the pilot wastewater treatment plant operated at the CSCI group. A SolfPLC, rather than a standard industrial PLC, is used because it provides much more flexibility when performing experimental studies. On the other hand, this is a biotechnological pilot-plant and it is imperative to provide round-the-clock and fault-tolerant control. Otherwise, the biomass may degrade rapidly, thus making it unusable. The presented control system consists of a main program running on a PC computer and a shadow program running on the FieldPoint real-time controller. The shadow program monitors the main program and if a failure is sensed, it takes over control of the process. Other mechanisms are implemented in order to ensure a proper cooperation between the main and the shadow program.