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# Prediction of-failure-rates-2009-03-30-v01

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Why Grundfos does not use MTBF. A very wise and useful policy.

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• i think most REs know the content of the presentation..the question is, what method/approach do you use?

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### Prediction of-failure-rates-2009-03-30-v01

1. 1. Prediction of Failure Rates Lars Rimestad, 2009-03-30 1
2. 2. History of Reliability US Dept. Of Defence: Military systems => extreme failure rates AGREE (1952):50 •Reliability = integral part of development19 •Derating •Test @ high Stress @ 1000’s of hours 60 •MTBF & Statistics 19 70 19 80 19 90 19 00 20 2 AGREE: Advisory Group on Reliability of Electronic Equipment
3. 3. History of Reliability MIL-HDBK-217 (1962) started5019 •Failure rate is constant (λ) 60 19 •MTBF = 1/ λ 70 19 MIL-HDBK-217 cancelled 80 19 90 19 t. 2 no 00 : F- -2 8 20 - 02 3 95 19
4. 4. Predicting the failure rate, MIL-HDBK-217Electrolytic capacitors:λP = λbπ CV π Qπ E Failures / 10 hours 6Microprocessors:λP = (C1π T + C2π E )π Qπ L Failures / 10 hours 6 • • • For the entire system: i =n 1 λSYSTEM = ∑ λP ,i ⇒ MTBFSystem = i =1 λSystem 4
5. 5. Necessary assumptions for prediction:•Constant failure rate •1 Toyota for 7.000 hours = 7.000 Toyota’s for 1 hour •A new car fails just as often as an old car that has run 300.000 km•System = sum of its components•No tolerance problems. No interface problems.•SW quality doesn’t matter! •1 line-of-code identical to 70.000 lines-of-code•Mechanical quality doesn’t matter! •However, you can use NPRD-95 (Non-electronic Parts Reliability Data), which is much less refined than MIL-HDBK-217•All system manufacturers have identical production quality•Only 14 different environments (of which 11 are military)•The authors of MIL-HDBK-217 know the quality of your product. 5
6. 6. Basic belief for the use of MIL-HDBK-217- And it’s many sisters: HRD-5, RDF-2000, Italtel, Telcordia/Bellcore … •Product reliability is inherent in the components. When a component fails, the cause should be found in the component itself. •This was more true in the 1960’ies when the failure pattern was caused by many electronic component defects, due to low production quality. •Today, this viewpoint is obsolete.Grundfos does not use this type of reliability prediction. 6
7. 7. ”To meet any reliability objective requires comprehensiveknowledge of the interaction of failure mechanisms, failuremodes, the mission profile, and the design of the product.” J1879, Handbook for robustness validation of semiconductor devices in automotive applications 7