Accendo Reliability

Your Reliability Engineering Professional Development Site

You are here: Home / Archives for Fred Schenkelberg

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 13 Comments

The Business of Providing MTBF

The Business of Providing MTBF

What Price Providing MTBF?

What good is your service if your livelihood consists of providing MTBF upon request?

Sure, you earn some money, yet did the customer receive value in the transaction? As you know, or should know, MTBF is so commonly misunderstood that the customer is likely to be confused about what they want, reliability or MTBF. Providing them with MTBF does not answer their question.

Worse, the customer thinks they got something of value and blithely heads off with rather meaningless information.

My contention is to provide MTBF because the customer’s request is wrong. We know better. Those performing predictions, doing data analysis, and other reliability engineering work know that MTBF is a faulty and rather meaningless metric often confused with reliability, R(t). (probability of success over a duration). [Read more…]

by Leave a Comment

The Many Ways of Data Analysis

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…]

by Leave a Comment

Fundamentals of Pareto Analysis

Fundamentals of Pareto Analysis

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…]

by Leave a Comment

High MTBF with Low Reliability

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 18 Comments

How About Weibull Instead of MTBF?

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…]

by Leave a Comment

Use Lognormal Distribution

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 1 Comment

Fundamentals of Hypothesis Testing

Fundamentals of Hypothesis Testing

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…]

by Leave a Comment

Culture Still Eats Strategy for Breakfast

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.

[Read more…]

by

Arrhenius or Erroneous

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

[Read more…]

by Leave a Comment

Fundamentals of Process Capability

Fundamentals of Process Capability

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 10 Comments

Acceleration Factors

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…]