Should I Use TTF or TBF Calculations?
Abstract
Kirk and Fred discussing comments we have received throughout the history of “Speaking of Reliability”. In this podcast we discuss one of the questions “should I calculate an average MTTR or MTBF ? “. We review the reasons that calculating an average time to or between failures does little to help make more reliable systems.
Key Points
Join Kirk and Fred as they discuss the continued reliance and belief that failure averages are not the best approach to reliability improvement and can be misleading.
Topics include:
- What are the reasons one would want to calculate averages of failures and what is it that they are trying to achieve.
- How some ignore warning signs of wear out failure due to loss of income for capital hardware (truck brakes squealing)
- How much margin, such as the point of warning (squealing brakes) to ultimate failure (loss of braking) is an unknown factor and risk.
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Show Notes
To read Fred’s post “Are we teaching reliability all wrong?” click on this link
For Kirk’s most popular post on Accendo Reliability, “Why the Drain in the Bathtub Curve Matters” , click on this link
For more information about Kirk’s Consulting services, please see his Accelerated Reliability Solutions website please click here
To see or purchase Kirk’s new book co-authored with John Paschkewitz, “Next Generation HALT and HASS: Robust Design of Electronics and Systems” please click on this link.
We always appreciate your feedback and questions. Thanks for listening.
Good discusssion. Based on what you described, it is a repairable system, so while you could compute an MTTF, it would not be particularly meaningful for decision makers. MTBF is for repairable systems. Fred’s main issue with MTBF, and I agree, is that you don’t know if the failure process is stationary or nonstationary. If is nonstationary, then there is a trend and MTBF masks that trend. However, you should want to test whether the trend is meaningful or significant. Peng Wang and I wrote a paper about that for the 2005 RAMS conference.
“Repairable Systems Reliability Trend Tests and Evaluation,” Peng Wang & David Coit, Proceedings of the 2005 Reliability & Maintainability Symposium (RAMS), Alexandria, VA, January 2005.
Dave,
Thanks for being a listener, your references, and your feedback.
Kirk