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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 may have tumesce 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 totally 50% longer. 9.3 REDUNDANCY LIMITATIONS The results for active and standby dependableness presented wherefore far ar 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 dominant in determine the level of reliability which can be achieved. For active agree systems, third estate mode sorrows and send sharing phenomena tend to be of most concern. For standby systems, shifting failures and failure of the standby unit before switching are important considerations. Common-Mode Failures Common-mo de failures are caused by phenomena that create dependencies between both or more redundant components which cause them to fail simultaneously. much(prenominal) 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 livelihood problems, or a drove of other factors. In moneymaking(prenominal) aviation, for example, a great deal of redundancy is employed, bothowing high levels of base hit to be achieved. Thus when problems do occu r frequendy 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 trail 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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