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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.

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Expectation and Moment Generating Functions

Expectation and Moment Generating Functions

In statistics and reliability, we use distributions to describe time to failure patterns. The four functions commonly used in reliability engineering include

  • The probability density function
  • The cumulative distribution function
  • The reliability function
  • The hazard function

We often use terms like, mean, variance, skewness, and kurtosis to describe distributions (along with shape, scale, and location). The mean is defined as the use of a moment generating function. First though let’s first back up to the concept of center of gravity (cog) from mechanics. [Read more…]

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Censored Data and CDF Plotting Points

Censored Data and CDF Plotting Points

Reliability testing and data collection is a messy business.

We rarely receive perfect data where all units involved have a precise time to failure record. Sometimes we do not the precise time to failure information or some of the units are still operating.

The data is censored.

There are a few common types of censoring, each of which has statistical techniques to appropriately account for the unknown elements. [Read more…]

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How to Assess Your Reliability Program

How to Assess Your Reliability Program

“How do you know so much about our program?” was a question the quality manager asked after reading the assessment report. The assessment took one day with eight interviews.

The reliability that results is going to happen whether or not the team designing the product or production line deliberately use reliability engineering tools or not. The elements of a product or system will respond to the environment and either work or fail.

While working at Hewlett-Packard I had the opportunity to conduct reliability program assessment of about 50 product divisions. One hypothesis related the number of reliability tasks the team actively used would correlate to their warranty expenses.

That worked to a point. [Read more…]

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4 Electronics Nondestructive Evaluations

4 Electronics Nondestructive Evaluations

It is possible to use the circuit design or the circuit itself to evaluate electronics. This ranges from checking if the system is wired correctly (the right parts are present and attached properly) to a complex evaluation including the proper functioning of firmware and attached software.

Beyond visual inspection, we need a way to evaluate the microscopic structures with today’s electronic components.

The ability to provide inputs and measure outputs provides one view and in most cases is nondestructive. [Read more…]

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Reliability Risk Reduction Tools

Reliability Risk Reduction Tools

The process to create a new product has risk. There are safety, technical, schedule and financial risks
The risk of a product failing more often then deemed acceptable by the customer or the business falls in the realm of reliability engineering to address.

We can provide insight on what is expected to failure and when. Working with the entire team we can influence the design and assembly process to minimize the risk of field failures.

Below is a short list the most common risk reduction tools in our arsenal. [Read more…]

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8 Nondestructive Evaluation Techniques

8 Nondestructive Evaluation Techniques

There are times when we need to evaluate a product to determine is it assembled correctly or when looking for clues concerning a failure mechanism. Simple visual inspection may be sufficient and there are times when we need more information or detail.

A great first step is the use of an appropriate nondestructive evaluation (NDE) method.

Done correctly, we keep the item unchanged and available for shipment or further inspection.

[Read more…]

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8 Factors of Design for Maintainability

8 Factors of Design for Maintainability

The first time I changed the oil filter of my car (first car in high school) I smashed my knuckles against a grimy block of metal. More than once. It may have been my lack of experience or improper tools. Or, it may have been a rather poor design.

Watching the Indy 500, especially the pit stops, I quickly realized there has to be something different about those cars that lets them change tires, add oil & fuel, and clean the windshield in less time than it took me to get under the hood and find the oil filter. The cars were designed differently and that is what permitted the difference in service time.

In order to increase availability and minimize the cost of maintenance, we have to deliberately design the system to accommodate the needs of maintenance. [Read more…]

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Big Picture of Reliability Plans

Big Picture of Reliability Plans

Reliability is an attribute of an item. The item, with its design, assembly, and use, has a finite probability of working over some duration.

We deliberately attempt to create items that meet our and our customer’s expectations concerning that probability and duration. We maintain and operate our equipment with an expectation of successful performance.

We and our customers are let down when a failure occurs. We do not enjoy the benefits of the item’s value. [Read more…]

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Reliability is Not Just Statistics

Reliability is Not Just Statistics

In a common definition used by engineers reliability is a probability of success. It is the chance of an item operating as expected over some duration in a given environment. In this case, we have probability as part of the definition of reliability.

Reliability in common use definition includes trustworthiness, dependability and similar definitions. It’s more than how many times your friends help you move to a new apartment, it’s a feeling or sense we have concerning our ability to count on our friends for the help.

[Read more…]

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Reliability and Cost Reduction

Reliability and Cost Reduction

I do not like procurement organizations.

It is like saying you don’t like lawyers. I don’t know all procurement engineers or managers, so understand my statement is a grand generalization. It’s not the people I don’t like, it’s a common behavior that I’ve witnessed countless times that I do not like.

Procurement organizations tend to look for ways to reduce cost by purchasing less expensive components or materials. This is often done with little regard to the impact on product reliability.

Why is this? And what can we do as reliability professionals to change this behavior? [Read more…]

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Field Industry and Public Failure Data

Field Industry and Public Failure Data

Beyond understanding what will fail (failure mechanisms) we need to know when a system will fail. Both kinds of information can be found in a variety of sources.

Unlike the stock market where we are regularly warned that past performance does not indicate future performance; in reliability engineering past performance is the best predictor of future performance. [Read more…]

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To Change the Reliability Culture

To Change the Reliability Culture

Have you ever wished your organization would work together to achieve a reliable product? Not just a few individuals and a heavy reliance on the reliability team to focus on highlighting and fixing reliability issues.

Some organizations tend to react to reliability issues. Prototype testing and field returns continue to surprise the team. The worst organization fall into finding someone to blame. Better organizations set to work to understand the problem and quickly resolve the issue. Some have better ‘fire departments’ than others.

Responding quicker is not really the best way to deal with reliability. [Read more…]