Redundancy method used in PLC related applications

PLC related applications are more complex as far as more components are involved. If some error occurs, diagnosis can take some time, but a logical procedure will shorten the time needed to locate the fault. The probability of failure of different parts of typical PLC systems shows that 95% of PLC systems are external faults and occur on plant items such as: sensors, actuators, transducers, limit switchers, and others. The possibility of determining the validity of the data gathered from all transducers of the control system assures a way of short time fault detection. Consequently, a fault-tolerant control system must be implemented using redundant structures, representing an alternative for malfunctioning element detection. This paper presents a method used to design and implement a control system based on redundant structures. A case study for the geothermal power plant at the University of Oradea was developed. The redundant structure considered was simulated using MathLab/Simulink and analyzed using different scenarios. Finally, a possible implementation of resulting control system structure is done using a programmable logical controller (PLC).