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L10_ECE4001_Spring_2010

# L10_ECE4001_Spring_2010 - Lecture 10 Reliability measures...

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J. Stevenson Kenney © 2010 1 Lecture 10: Reliability measures and prediction; System reliability February 15, 2010

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J. Stevenson Kenney © 2010 2 Reliability Engineering • Criticality varies with industry – Consumer electronics • Whatever market will bear • Usually not critical – Automotive electronics • Safety issues More critical – Space program • Highest level of reliability • Reliability Engineering is concerned with estimating the probability of failure and designing with enough margin to achieve an acceptable failure rate or lifetime. Reference: A. Birolini, Reliability Engineering , 3 rd ed., Springer, 1999.
J. Stevenson Kenney © 2010 3 A typical problem: Your company has developed a new microcontroller. A lot of 1000 units is tested for 2000 hours, after which 500 good units remain. What is the is the probability that one unit will have failed after in the first 100 hours of operation?

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J. Stevenson Kenney © 2010 4 Probability of Failure Let F(t) be the define the probability of failure probability fa f(t) as: ilure den () sity d ft F t dt = It follows that: ( ) ( ) 0 and that: 1 t Ft f d F τ = ∞=
J. Stevenson Kenney © 2010 5 Define R(t) as: R(t) = 1 - F(t), or R(t) reliabilit + F(t y ) = 1 () () 0 Differentiating gives dd Rt Ft dt dt dt dt += =− Reliability (Survival Rate)

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J. Stevenson Kenney © 2010 6 O F S F OS number of failures per unit time t Total failed survived number of units at time t=0
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L10_ECE4001_Spring_2010 - Lecture 10 Reliability measures...

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