Slides - Åbo Akademi
Slides - Åbo Akademi Slides - Åbo Akademi
Failure Rate Estimation The failure rate is often assumed to be constant (this assumption simplifies calculation) Often no other assumption can be made because of the small number of available event data In this case, an estimator of the failure rate is given by: where λ = N f T f , – N f – number of failures observed during operation – T f – cumulative operating time
Example: Failure Rate Calculation Failure rate calculation example Ten identical components are each tested until they either fail or reach 1000 hours, at which time the test is terminated for that component. • Ten Theidentical results components are: are each tested until they either fail or reach 1000 hours, at which time the test is terminated for that component. The results are: Component Hours Failure Component 1 1000 No failure Component 2 1000 No failure Component 3 467 Failed Component 4 1000 No failure Component 5 630 Failed Component 6 590 Failed Component 7 1000 No failure Component 8 285 Failed Component 9 648 Failed Component 10 882 Failed Totals 7502 6 The estimated failure rate is: Estimated failure rate is: 6 failures 7502 hrs = 799.8 · 10−6 failures/hr or or =799.8 failures for every million hours λ of = operation. 799.8 failures for every million hours of operation. 12 April 2007 8
- Page 1 and 2: Software Safety Lecture 8: System R
- Page 3 and 4: Reliability Definition Reliability:
- Page 5 and 6: Safety-critical Systems • Pervasi
- Page 7 and 8: Hardware Failures The system is sai
- Page 9 and 10: Failure Rate (ctd.) Classification
- Page 11 and 12: Most Important Distributions Discre
- Page 13 and 14: Reliability Parameters MTTF: Mean T
- Page 15 and 16: Exponential Distribution The distri
- Page 17: MTTF Example A system with a consta
- Page 21 and 22: Series Systems Such a configuration
- Page 23 and 24: Series-Parallel Combinations The mo
- Page 25 and 26: M-of-N Arrangement A system consist
- Page 27 and 28: Failure rate The term failure inten
- Page 29 and 30: Design diversity Each variant of so
Example: Failure Rate Calculation<br />
Failure rate calculation example<br />
Ten identical components are each tested until they either fail or reach<br />
1000 hours, at which time the test is terminated for that component.<br />
• Ten Theidentical results components are: are each tested until they either fail or reach 1000<br />
hours, at which time the test is terminated for that component. The results<br />
are:<br />
Component Hours Failure<br />
Component 1 1000 No failure<br />
Component 2 1000 No failure<br />
Component 3 467 Failed<br />
Component 4 1000 No failure<br />
Component 5 630 Failed<br />
Component 6 590 Failed<br />
Component 7 1000 No failure<br />
Component 8 285 Failed<br />
Component 9 648 Failed<br />
Component 10 882 Failed<br />
Totals 7502 6<br />
The estimated failure rate is:<br />
Estimated failure rate is:<br />
6 failures<br />
7502 hrs = 799.8 · 10−6 failures/hr<br />
or<br />
or =799.8 failures for every million<br />
hours λ of = operation. 799.8 failures for every million hours of<br />
operation.<br />
12 April 2007 8
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