PLC-ASSISTED INSPECTION AND COLD-STANDBY LUBRICATION IN CEMENT GRINDING: STOCHASTIC RELIABILITY, SWITCHING COVERAGE AND ECONOMIC THRESHOLDS

Programmable logic controller (PLC) alarms and lubrication standby systems can potentially reduce the consequences of developing faults, but their reliability gains depend on inspection delays, switching success and maintenance expenditure. This paper compares two policy bundles for a cement grinding system using stochastic state models: Model III provides PLC-assisted inspection followed by repair or replacement, whereas Model IV incorporates a proposed cold-standby lubrication-pump subsystem with automatic PLC switching and restoration. Both scenarios are based on a observed, 24-month operating workbook containing 214 fault events, 325 PLC alarm records and 24 illustrative standby-test records. In the inspection model, a regenerative first-passage expression accounts for competing minor-fault escalation and inspection completion. In the standby model, a ten-state continuous-time Markov particular case accounts for an active primary pump, dormant standby failures, switching coverage, backup operation and unprotected non-pump faults. The previously developed thesis baselines give mean time to sustained system failure of 219.23 h and 251.24 h, binary availability of 98.27% and 98.63%, and expected profit of ₹90,265.27/h and ₹90,552.48/h, respectively. Equation-derived sensitivity results show why incomplete switching coverage and active-backup failures restrict the effectiveness of redundancy. The apparent profit advantage is lost when additional unbudgeted standby expenditure exceeds approximately ₹287.21/h, all other scenario assumptions held constant. The comparison is illustrative rather than causal: the two models differ in several intervention assumptions, and neither strategy has been validated on installed equipment. The proposed framework supports transparent screening of inspection and redundancy investments prior to field trials.