2025, Vol. 10, Issue 8, Part C

This paper examines the reliability of a Programmable Logic Controller (PLC) system with hardware redundancy by performing preventive maintenance on the standby unit after it has operated for a specific period. There are possibilities of two scenarios: either the active unit undergoes a software upgrade with a certain probability, or it suffers a hardware failure independently with another probability after its preventive maintenance (PM). If any issue arises, a serviceman is immediately available to handle both software and hardware repairs as well as maintenance. After repairs, the system is assumed to return to full working condition. Hardware and software failures are modeled using exponential distributions, while other events follow arbitrary distributions. The analysis uses the Regenerative Point Graphical Technique (RPGT) combined with a semi-Markov process to efficiently evaluate reliability metrics and system behavior. Results include tabulated expressions for key parameters such as Mean Time to System Failure (MTSF), system availability & profit.