The MTTF and reliability evaluation of a PLC system

This paper presents the evaluation technique of the mean time to failure (MTTF) and reliability corresponding to a programmable logic controller (PLC) structures such as a single controller, a dual controller and a triple modular redundancy (TMR) controller. The failure and repair period of PLCs are surveyed, and the failure rate of each unit composing a PLC is calculated. The MTTF of a single PLC system and a dual PLC system is computed with failure rate and compared. Reliability and MTTF with respect to a dual controller and a TMR controller are calculated and analyzed by using the Markov model in order to present the operation standards of a PLC.X11sciescopu