Unpowered to Powered Failure Rate Ratio: A Key Reliability Parameter

The unpowered to powered failure rate ratio (λ'/λ) is a key system reliability design parameter. An initial assumption of this ratio can greatly influence a system design. Furthermore, some system configurations, e.g., parallel system, are much more sensitive to this ratio than other configurations, e.g., TMR/Spares system. However, regardless of which standby redundancy technique is considered, the system reliability dependence on this key parameter increases as the number of standby spares increases. Currently available published statistical data on λ and λ' are not consistent enough to be a useful design aid for system designers. Thus, an effort needs to be made to correlate these data and/or obtain additional, better defined and substantiated data.