Reliability

1

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

2

Inherent Reliability is Designed Reliability

• Found by reliability testing

3

Achieved Reliability is Empirical

4

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

over

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Failure Rate, lambda, is units per hour

• lambda = number of failures/total unit operating hours

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Mean Time to Failure MTTF (non repairable) or Mean Time

Between Failure MTBF (repairable items) is theta =

1/lambda

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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

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

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Reliability of process with Tasks in Serial

• R1 times R2… times RN

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Reliability of process with steps in parallel

• 1-(1-R1)(1-R2)(1-Rn)

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Redundancy and Apollo 13

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