S.M. Rizwan, V. Khurana, and G. Taneja


Programmable logic controller (PLC), failures, repairs, semi-Markov Process, regenerative processNotations o hs λ α γ p1 p2∗operative unit hot standby unit constant failure rate of the operative unit constant failure rate of the hot standby unit inspection rate probability of failure (repairable) probability of replacement of type I failure (RB/PSF)probability of replacement of type II failure (Burnt) p4 probability of SC failure Fi failed unit is under inspection Fwi failed unit is wait


Industries/plants, such as Fibre Optic plant and casting plants, often use programmable logic controllers (PLC) as a two-unit/twoPLC hot standby systems. Optimizing profit and avoiding the major losses are the main objectives of using a two-unit hot standby PLC system. In the two-unit system, one unit is operative and the other is a hot standby. The hot standby unit also fails, but with lower failure rate than the operative unit. The paper outlines a reliability analysis of a two-unit hot standby PLC system, and the real data from an industrial system has been used for the purpose. Four types of failure are seen in the PLCs: input module failure, digital relay burnt/power supply failure, complete unit burnt failure and failure due to corrupted software. The concept of inspection is introduced to detect the type of failure. The model developed is embedded by the types of failure actually depicted in the data and the real failure, repair, replacement, reinstallation rates are used for analysis. Measures of system effectiveness in terms of reliability indices are obtained using semi-Markov processes and regenerative point techniques. shown. Profit incurred to the system is evaluated and related graphs pertaining to the case example are also

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