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How to measure reliability 2
The document discusses the concept of reliability as the probability that a product, system, or service will perform its intended function over a specified period without failure. It emphasizes the importance of accurate measures of reliability and cautions against blindly following mean time between failures (MTBF), as it may lead to incorrect strategies. Additionally, it outlines the necessity of proper tools and understanding of reliability to make informed decisions in areas such as maintenance, inspection, and risk management.
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How to measure reliability 2
- 1. Ammar Alkhaldi Real Reliability 2April 2016 PART 2: Begin with the end in mind How to Measure Reliability
- 2. Use reliability tomeasure reliability Sound obvious… Reliability is probability that a product, system or service will perform its intended function adequately for a specified period of time, operating in a defined operating environment without failure. So it’s a probability, for specific time (t).
- 3. Use reliability tomeasure reliability Sound obvious… Reliability is probability that a product, system or service will perform its intended function adequately for a specified period of time, operating in a defined operating environment without failure. So it’s a probability, for specific time (t). This summon the magical reliability function 𝑅(𝑡)
- 4. Reliability function inaction 𝑅(𝑡) Vs. MTBF (MTxx) Or any another
- 5. Diode MTTF =20 YearDiode MTTF = 20 Years Reliability function in action USER B So the average life of the population is 20 years, and if the Standard Deviation = 1 year then 99% of the relays will fail within 17-23 years. Now I’ll set my strategy USER A So 50% of the population will fail after 20 years. Now I’ll set my strategy How can “taking MTBF value as it is” lead to wrong strategy
- 6. Diode MTTF =20 YearDiode MTTF = 20 Years Reliability function in action USER B So the average life of the population is 20 years, and if the Standard Deviation = 3 years then 99% of the relays will fail within 17-23 years. Now I’ll set my strategy USER A So 50% of the population will fail after 20 years. Now I’ll set my strategy How can “taking MTBF value as it is” lead to wrong strategy
- 7. Diode MTTF =20 Years Reliability function in action USER C Will assume: A. The vendor calculate the MTTF in the right way. B. Constant failure rate (i.e. exponentially distributed). How can “taking MTBF value as it is” lead to wrong strategy 𝐹 𝑡 = 1 − 𝑒−𝜆𝑡, MTTF= 1/𝜆 Do the math Where 𝜆= failure rate, 𝑡 = Time 𝑅 𝑡 = 1 − 𝐹 𝑡 𝑅 1 𝑌𝑒𝑎𝑟 = 1 − (0.0487) = 95.1% Reliability by the first year 𝑅 20 𝑌𝑒𝑎𝑟𝑠 = 1 − (0.632)= 36.8 % Reliability by 20 years
- 8. Diode MTTF =20 Years Reliability function in action USER C Will assume: A. The vendor calculate the MTTF in the right way. B. Constant failure rate (i.e. exponentially distributed). How can “taking MTBF value as it is” lead to wrong strategy 𝐹 𝑡 = 1 − 𝑒−𝜆𝑡, MTTF= 1/𝜆 Where 𝜆= failure rate, 𝑡 = Time 𝑅 𝑡 = 1 − 𝐹 𝑡 𝑅 1 𝑌𝑒𝑎𝑟 = 1 − (0.0487) = 95.1% Reliability by the first year 𝑅 20 𝑌𝑒𝑎𝑟𝑠 = 1 − (0.632)= 36.8 % Reliability by 20 years IS THIS WHAT EXPECTED BY 20 YEARS MTTF ???
- 9. Diode MTTF =20 Years Reliability function in action USER C Now let’s come to the assumptions Will assume: A. The vendor calculate the MTTF in the right way. B. Constant failure rate (i.e. exponentially distributed). A. Testing 12 diodes for 1month doesn’t reflect 1year reliability nor introducing all the failure modes, if the data provided by the vendor s not accurate then this assumption is wrong, using your own field data is better and reflecting the real running environment, ask the vendor how the ALTA was done. How can “taking MTBF value as it is” lead to wrong strategy
- 10. Diode MTTF =20 Years Reliability function in action USER C Now let’s come to the assumptions Will assume: A. The vendor calculate the MTTF in the right way. B. Constant failure rate (i.e. exponentially distributed). B. For electronics components, assuming constant failure can be acceptable (in fact it’s a random failure rate) since the constant failure rate phase aka useful life phase can be long enough for the components to fail due to the random failures before it even reach the wear out phase. What if it wasn’t constant failure rate How can “taking MTBF value as it is” lead to wrong strategy
- 11. What if itwasn’t constant failure rate In this turbine’s winding Example it’s clear That the exponential distribution is not fitting The failure data. In such case we won’t be able to determine the reliability function given MTBF value alone. We need special tools to find the 𝑅(𝑡) Credit to blog.minitab.com
- 12. Why vendor stillusing MTBF ? 20 years MTBF sound much better than “There is 63.2 % chance our component will fail by 20 years”. Specially if the competitors still using MTBF furthermore customers even asking for it.
- 13. Calculating the reliabilityfunction
- 14. Begin with theend in mind First thing we need to do before measuring reliability, is to ask this question:
- 15. Begin with theend in mind First thing we need to do before measuring reliability, is to ask this question: Why are we measuring the reliability ?
- 16. Begin with theend in mind
- 17. Begin with theend in mind Does it really matter ? Can’t we just measure it now and decide later ? Actually I might use one tool for multi purposes!
- 18. Begin with theend in mind Yes it does matter. Reliability is a little bit different, We have different tools, each have its own usage Does it really matter ? Can’t we just measure it now and decide later ? Actually I might use one tool for multi purposes!
- 19. Begin with theend in mind Does it really matter ? Can’t we just measure it now and decide later ? Actually I might use one tool for multi purposes! The wrong tool will give a wrong (misleading) result.
- 20. WHY? • Preventive Maintenance •Spare parts strategies • Inspection scheduling • Warranty • Benchmarking • Risk assessment • Risk mitigation WHAT? • Component/System • Repairable/Non-Repairable • HOW? • Life data analysis (Weibull) • Reliability Growth • Reliability Block Diagram (RBD) • And many other tools
- 21. If you areinterested how to use some of these tools, stay toned for the upcoming post. Salam Ammar Alkhaldi, CSSBB How to use reliability tools
- 22. NO MTBFBlog http://nomtbf.com/ SIEMENS Background information on MTBF http://www.weibull.com/hotwire/issue22/hottopics22.htm http://blog.minitab.com/blog/understanding-statistics/choosing- the-right-distribution-model-for-reliability-data References
- 23. Feel free toshare it, but don’t change it Except where otherwise noted, this work is licensed under Attribution-NonCommercial-ShareAlike 4.0 International