All posts by Fred Schenkelberg

About Fred Schenkelberg

I am an experienced reliability engineering and management consultant with my firm FMS Reliability. My passion is working with teams to create cost-effective reliability programs that solve problems, create durable and reliable products, increase customer satisfaction, and reduce warranty costs.

How to have clear reliability conversations

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 concern about MTBF

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

Continue reading Voicing concern about MTBF

Is MTBF better than nothing

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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Difference between hazard and failure rate

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.

Continue reading Difference between hazard and failure rate

Calculating reliability from data

In the last note, we calculated MTBF using some test data. Now let’s start with the same situation and calculate reliability instead. As before: There are occasions when we have either field or test data that includes the duration of operation and whether or not the unit failed.

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Calculating MTBF from data

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. Continue reading Calculating MTBF from data

MTBF to PoF

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. Continue reading MTBF to PoF

Reality

wpid-reality-2013-09-8-09-44.jpg Phillip K. Dick (Brain Pickings, http://www.brainpickings.org/index.php/2013/09/06/how-to-build-a-universe-philip-k-dick/) Or stated another way

Reliability, is that which when you stop measuring it doesn’t go away.

Product’s fail. That is a reality. It is messy, confusing and not always obvious why. Product fail. They cease to function, they are the wrong color, they are too expensive, they were a mistaken purchased, or they degrade, crack, discolor, or fracture.

Continue reading Reality

Clarity

Moving toward clarity reliably

I recently saw a quote with the notion to stop complaining and do something positive. Which happens to work with my mother’s admonishment

If you have nothing good to say, say nothing.

So, while I’ve been railing against MTBF and then suggesting a better metric, my message on use something else has gotten lost. Recently on a Linkedin group discussion someone suggests yesbx.com as a sister site to nomtbf.com.

Maybe it is time to focus on a positive message around a replacement metric to MTBF. You already know my position on MTBF. So what do I recommend. Continue reading Clarity

Learning Reliability

Learning Reliability … Or, reliable learning.

One of the best things about reliability engineering is the never ending opportunity to learn. We work with materials, assembly processes, and people creating and maintaining products, machines, and systems. Other engineering disciplines tend to focus on one aspect of a design or process – mechanical engineers make allowances for the circuit board location and heat transfer requirements, yet do not word on the circuits themselves.

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End MTBF Debating

The End of MTBF Debating

Endless debate on merits of MTBF is meaningless as more than one has told me. My neighbor has a bumper sticker that says Endless War with the ‘less’ crossed out and written above it ‘this’. Instead of endless debate, how about we just end this now. Stop using MTBF and all related grand averages. Use the statistics, distributions and knowledge you have to provide accurate estimates and summaries.

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