The importance of conversations

Wayne Nelson once said during a conference, “The words we use matter”. I agree. I think using MTBF in conversation should be avoided. This is not a surprise those that know me.

We do and should have meaningful conversations about reliability. To improve those conversations consider the words you use. Reliability is the probability of survial over some duration for stated set of conditions and expected function. It is the probability and duration that often gets muddled.

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Voicing Concerns about MTBF

In January 2006, Jim Renfroe, Executive Vice President (Retired), Haliburton, published an essay titled,

Interpreting Reliability Metrics with Confidence. He discussed reliability, it’s defintion, importance, and working with suppliers to achieve higher product reliabilty. He also said,

MTBF or MTTF can be misleading

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Is using MTBF better than not using any reliability measure?

This is the core of a blog entry mean-time-between-failure-why-people-do-not-use-the-1-metric-for-equipment-reliability by Ricky Smith, ” Mean Time Between Failure Why People Do Not Use the 1 Metric for Equipment Reliability” (which seems to be removed from his blog at the moment) a few months ago. The recommendation and example described highlights the benefit of using MTBF over not making any reliability measurements.

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I too have found these terms used interchangeable in many papers and references.
(This note is in response to a question on a forum asking about the difference between these two terms. The question prompted some interesting discussion and no clear resolution as various authors and authoritative works do not seem to agree.

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There are occasions when we have either field or test data that includes the duration of operation and whether or not the unit failed. This can be, say, 10 large motors. For sake of argument, the test ran each motor for 1,000 hours and when a motor failed it was repaired quickly and returned to the test. There were 3 failures. [Read more…]

Received this questions the other day.

So if we were to go from a MTBF requirement of 7,500 hours @ 40 degrees C how would we address this requirement as a PoF? Would we say the PoF is 90% reliable after 7,500 hours of operation? Or would we state this as something else?

The discussion is on how to move towards using physics of failure (PoF) type approaches rather than parts count. The underlying question is about how to set reliability goals. [Read more…]

JUST DON’T USE IT….PERIOD – a comment by Barry Snider