cpe317-lec1 - CpE 317 CpE Fault-Tolerant Digital...

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Unformatted text preview: CpE 317 CpE Fault-Tolerant Digital Fault-Tolerant Systems Systems Dr. Minsu Choi Fundamentals of Reliability Part 1 Lesson Topics Lesson Reliability and failure rate Relation between Reliability and MeanTime-to-Failure (MTBF) Maintainability Availability Series and parallel system Reliability and Failure Rate Reliability N iidentical components under dentical conditions. conditions. S(t) is the # of components S(t) still operating at time t. still F(t) is the # of components that have F(t) upto time t. Then the probability of survival of the Then components, aka reliability R(t), is… components, Continued, Continued, Reliability Unreliability Failure Rate Failure Failure rate, aka , is Failure defined to be the # of failures per unit time compared with the # of surviving components. components. Variation of failure rate with time Variation Early life period – in any large collection of Early components there are usually components with , and these fail. with Useful life period – the failure rate is Useful relatively - failures are in time. Wear-out failure period – the failure rate Wear-out begins to increase rapidly with time. begins Bathtub Curve Bathtub Exponential Failure Law Exponential In the useful life period, the failure rate is In constant, and therefore constant, Continued, Continued, Continued, Continued, Continued, Continued, Therefore, Therefore, The above relationship is known as the The . The failure rate is usually expressed as The percentage failures per 1000 hours or failures per hour. failures Simplification Simplification Series expansion System with Hybrid Components System If a system contains k types of If components, each with failure rate λt, then t, the system failure rate, , is where there are Nk of each type of compoment. compoment. Example Example Program Completed Program ...
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