Fred Schenkelberg — Thought Leader

Author of CRE Preparation Notes, Musings", NoMTBF, multiple books & ebooks>, co-host on Speaking of Reliability>/a>, and speaker in the Accendo Reliability Webinar Series.

This author's archive lists contributions of articles and episodes.

by Fred Schenkelberg Leave a Comment

The Many Ways of Data Analysis

Given Some Data, Do Data Analysis

Let’s say we have a set of numbers, {2.3, 4.2, 7.1, 7.6, 8.2, 8.4, 8.7, 8.9, 9.0, 9.1} and that is all we have at the moment.

How many ways could you analyze this set of numbers? We could plot it a few different ways, from a dot plot, stem-and-leaf plot, histogram, probability density plot, and probably a few other ways as well. We could calculate a few statistics about the dataset, such as mean, median, standard deviation, skewness, kurtosis, and so on. [Read more…]

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Fundamentals of Pareto Analysis

podcast episode with speaker Fred Schenkelberg

Pareto Analysis is a simple yet powerful tool that provides a visual way to help focus on the most critical tasks. The idea that 80% of your field failures come from 20% of the failure mechanisms is one way we can focus on the vital few instead of the insignificant many.

Let’s explore the basics of conducting Pareto Analysis, plus a few different ways to create and modify the plots. Of course, we’ll talk about some potential problems and pitfalls to avoid.

Bring your questions and success/failure stories using this tool. There should be plenty of time for a discussion.

[Read more…]

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High MTBF with Low Reliability

Can You Have a High MTBF and Low Reliability?

As regular readers know, MTBF by itself is misleading. It can also be deceptive when representing actual data. Just because you have a high MTBF value doesn’t mean it is reliable.

In a previous article, 10 Reasons to Avoid MTBF, I mentioned that it is possible to have a relatively high MTBF value when the actual reliability is low. Ashley sent me the following note:

Hi Fred, i love reading your articles they are very informative. I have a question about something you said in a comment which i am hoping you will be able to clarify for me. You said products with higher MTBF can actually be less reliable than products with a lower MTBF
I have tried to find information on how this is possible online, and tried to do the maths myself to make this happen but i have to admit i am struggling.

No worries, Ashley, let’s work out an example to illustrate what I meant. [Read more…]

by Fred Schenkelberg 18 Comments

How About Weibull Instead of MTBF?

What About Weibull? Can I Use it Instead of MTBF?

This was a follow-up question in a recent discussion with Alaa concerning using a metric other than MTBF.

The term ‘Weibull’ in some ways has become a synonym for reliability. Weibull analysis = life data (or reliability) analysis. The Weibull distribution has the capability to describe a changing failure rate, which is lacking when using just MTBF. Yet, is it suitable to use ‘Weibull’ as a metric? [Read more…]

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Use Lognormal Distribution

The lognormal distribution has two parameters, μ and σ. These are not the same as mean and standard deviation, which is the subject of another post, yet they describe the distribution, including the reliability function.

$$ \displaystyle R(t)=1-\Phi \left( \frac{\ln (t)-\mu }{\sigma } \right)$$

Where Φ is the standard normal cumulative distribution function, and t is time. [Read more…]

by Fred Schenkelberg 1 Comment

Fundamentals of Hypothesis Testing

podcast episode with speaker Fred Schenkelberg

Let’s make a comparison. Let’s check our product’s key characteristics against specifications, compare vendor life data, or compare the newest design changes to prior performance. We can and should do comparisons well using the appropriate statistical approach.

Let’s examine a handful of parametric and non-parametric comparison tools, including various hypothesis tests. Plus how to best use these tools and when to set them aside and explore another approach.

[Read more…]

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Join the Linkedin Group

The Linkedin NoMTBF group is growing and while not very active does have an occasional interesting discussion. Join the discussion and maybe relate how you have raised awareness around the proper use of MTBF.

https://www.linkedin.com/groups/1857182/

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Culture Still Eats Strategy for Breakfast

Guest Post by Bill Pomfret (first posted on CERM ® RISK INSIGHTS – reposted here with permission)

It took us years to move from top-down to people-centric management, but the journey was worth it Peter Drucker once said, “Culture eats strategy for breakfast.” Throughout my career, I have spent a lot of time in the strategy room. But no matter what we decided there, until we got the organizational culture right, we were unsuccessful in executing our goals.

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by Fred Schenkelberg

Arrhenius or Erroneous

The following is a recent discussion on the sister Linkedin NoMTBF Group. It was and may continue to be a great discussion. Please take a look and comment on where you stand. Do you have some form of the Arrhenius reaction rate equation in your reliability engineering work? Join the discussion here with a comment or on the Linkedin group conversion.

Fred

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Why HALT is not HALT

An excellent short white paper by Craig Hillman that is worth reading. It underscores why I claim HALT is the second worst 4 letter acronym in our profession.

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Fundamentals of Process Capability

podcast episode with speaker Fred Schenkelberg

Calculating and interpreting the process capability ratios is the easy part. Getting valid results takes more work and thinking. Knowing that the process is capable is only one use of this information. We should also use the information contained in these ratios to inform product design tolerance. [Read more…]

by Fred Schenkelberg 10 Comments

Acceleration Factors

Temperature acceleration factor for ALT planning (question posted to Linkedin Society of Reliability engineers group, 5/7/12

Hello, can anyone advise me how to calculate temperature acceleration factor for a complex system including cards, RF elements, cables, motors and moving parts? Is the Arrhenius model valid for such systems, or there are more precise models? Thank you!

[Read more…]

by Fred Schenkelberg Leave a Comment

System or Component Testing

Fred i was asked this question and wanted to know what your thoughts were on this. R and D asked me what was the criteria to decide if to test at a component level or at a system level , my answer was that it should depend on what is the reliability and confidence level of the component
your thoughts?

thanks
sd

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by Fred Schenkelberg 2 Comments

Parts Count Variation

Just a short post to point to a paper on the accuracy of part count prediction techniques. A few years ago, I recalled seeing a paper that studied the difference between various parts count methods and actual results.

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Graphical Analysis of Repair Data

With the kind permission of Wayne Nelson and Robert Abernathy, we are posting an article on the analysis of repair data. As you may know, the assumptions made when using simple time-to-failure analysis of repairable systems may provide misleading results. Using the analysis method outlined by Wayne is one way to avoid those costly mistakes.

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