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] ] 1 1 T T X MTTF, X MTTF, (1 - Vl - R) (1 - Vl - R) ?] ?] (1 - Vl - 0.9) (1 - Vl - 0.9) 1 1 X MTTF = 0.380 MTTF. X MTTF = 0.380 MTTF. Thus the purposeless system whitethorn have salutary four times the design life of the single system, diarrhoetic though it may be seen from Eq. 9.15 that the MTTF of the redundant system is completely 50% longer. 9.3 REDUNDANCY LIMITATIONS The results for active and standby reliableness presented therefore far are highly i pass aroundized. In practice, a function of factors can significantly reduce the reliability of redundant systems. In reality, these factors and their mitigation often are prevailing in determine the level of reliability which can be achieved. For active agree systems, third estate mode misfortunes and clog sharing phenomena tend to be of most concern. For standby systems, substitution failures and failure of the standby unit before switching are important considerations. Common-Mode F ailures Common-mode failures are caused by phenomena that create dependencies between dickens or more redundant components which cause them to fail simultaneously. such failures have the potential for negating oftentimes of the benefit gained with redundant configurations.

Common-mode failures may be caused by common electric connections, shared environmental stresses such as system or vibration, common concern problems, or a drove of other factors. In commercialised aviation, for example, a great deal of redundancy is employed, bothowing high levels of golosh to be achieved. Thus when problems do occur fre quendy they may be attributed to common-mode! failures: the dust rising from a volcanic eruption in Alaska that caused simultaneous malfunctioning of all of a commercial airliners engines, or the pieces of a fractured kilobyte engine turbine blade that apologise all of the redundant hydraulic control lines and caused the crash of a DC 10. Viewed irl terms of the reliability block diagrams in Fig. 9.2, commonmode failure mechanisms have the same takings as putting in an...If you want to get a full essay, order it on our website: OrderCustomPaper.com

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