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Reliability

This article explores the concepts of reliability and maintainability of products, emphasizing their significance in ensuring consistent performance under specified conditions. It distinguishes between functional and reliability failures, detailing the importance of maintainability and inherent reliability, which refers to the design phase of a product. The text also covers critical metrics like failure rate (λ), Mean Time to Failure (MTTF), and Mean Time Between Failures (MTBF), as well as the application of Poisson distributions in reliability functions. Real-world applications, including instances of redundancy illustrated by the Apollo 13 mission, are discussed.

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Reliability

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  1. Reliability

  2. Probability a product will perform as promoted for a given time period under given conditions • Functional Failure: does not operate as designed • Reliability Failure: does not operate as designed as long as it is supposed to • Maintainability: related to durability and refers to once a product breaks, what is the probability it can become functional again

  3. Inherent Reliability is Designed Reliability • Found by reliability testing

  4. Achieved Reliability is Empirical

  5. Infant Mortality Period: if it makes it by time x, then the constant failure rate takes over

  6. Failure Rate, lambda, is units per hour • lambda = number of failures/total unit operating hours

  7. Mean Time to Failure MTTF (non repairable) or Mean Time Between Failure MTBF (repairable items) is theta = 1/lambda

  8. For a given p of failure, what is the p of failure in a given time interval p = e ^ (-lambda (t2-t1)) • number happening in given time that is Poisson distributed which means the interval between is exponentially distributed

  9. Reliability Function R of given time (RT = e^(-lambda * T)

  10. Reliability of process with Tasks in Serial • R1 times R2… times RN

  11. Reliability of process with steps in parallel • 1-(1-R1)(1-R2)(1-Rn)

  12. Redundancy and Apollo 13

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