Fred Schenkelberg — Thought Leader

Author of <a href="/creprep/">CRE Preparation Notes</a>, <a href="/on-product-reliability/musings">Musings</a>, <a href="/articles/nomtbf/">NoMTBF</a>, <a href="/book-author/fred-schenkelberg/">multiple books & ebooks</a>, co-host on <a href="/series/sor/">Speaking of Reliability</a>, and speaker in the <a href="/series/sor/">Accendo Reliability Webinar Series</a>.

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

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Create a Meaningful Environmental Test Plan

We often want to know if our product will work as expected in our customer’s environment.

Creating an environmental test plan that clearly shows weaknesses and strengths should be part of your program for each product.

Let’s explore the steps and resources you should consider when creating an environmental test plan for each product.

We will discuss why using standards or even the plan from the last program may not provide you meaningful information.

Understanding how your product responds to your customer’s environment provides the information for your team to make improvements and improve product reliability.
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by Fred Schenkelberg 3 Comments

OC Curve with Binomial Method

The operating characteristic curve is useful to understand the capability of a lot sampling plan. It depicts a graphical relationship between the unknown lot’s defect rate and the probability of the specific sampling plan to accept the lot. Ideally, we want a sampling plan the correctly accepts good lots and rejects bad lots. [Read more…]

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The True Importance of Reliability Block Diagrams

A reliability block diagram is a graphical and statistical representation of the reliability structure of a system.

Graphical as an RBD is drawn with blocks for each element of a system and connecting lines representing the relationship between elements.

[Read more…]

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Sources of Variation

We have statistics to describe the variation that occurs in our world. Statistics is the language of variation.

If each of your produced products were identical in every way to all products produced, with no variability, we wouldn’t be concerned with the effect of variation on the performance and reliability of our designs.

Yet, variation does happen and we have a range of tools to identify and minimize the naturally occurring variation. [Read more…]

by Fred Schenkelberg 11 Comments

Fault Tree Analysis 8 Step Process

Fault Tree Analysis (FTA) provides a means to logically and graphically display the paths to failure for a system or component. One way to manage a complex system is to start with a reliability block diagram (RBD). Then create a fault tree for each block in the RBD.

Whether a single block or a top level fault for a system the basic process to create a fault tree follows a basic pattern. [Read more…]

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Break the “we’ve always done it this way” cycle

Reliability and test planning takes time and it’s easy to use the plan worked out for the last program.

Yet this doesn’t consider the new risks or technology or use conditions that impact product reliability.

If you find resistance as you propose improvements to the reliability plan or to the test plan, what can you do to gain acceptance?

If the source of resistance that what we did last time worked, why change, then what steps can you take to secure support for the needed changes?
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by Fred Schenkelberg 6 Comments

Benefits of Fault Tree Analysis

Is a logical, graphical diagram that organizes the possible element failures and combination of failures that lead to the top level fault being studied.

The converse, the success tree analysis, starts with the successful operation of a system, for example, and examines in a logical, graphical manner all the elements and combinations that have to work successfully.

With every product, there are numerous ways it can fail. Some more likely and possible than others. The FTA permits a team to think through and organize the sequences or patterns of faults that have to occur to cause a specific top level fault. The top level fault may be a specific type of failure, say the car will not start. Or it may be focused on a serious safety related failure, such as the starter motor overheats starting a fire. [Read more…]

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How to Break into Reliability Engineering

I’ve recently received a couple of notes from individuals looking at starting a career in reliability engineering. One is a student looking at a career path, another a working engineer with an interesting in reliability.

Both asked how to land a position given no reliability engineering experience.

Hum, I don’t know anyone that had reliability engineering experience before they got started working in reliability engineering. Not counting taking apart the family toaster and trying to repair it before Mom got home as a kid.

[Read more…]

by Fred Schenkelberg 7 Comments

The Range Rule

When time is short and you just want a rough estimate of the standard deviation, turn to the range rule to quickly estimate the standard deviation value.

The standard deviation is approximately equal to the range of the data divided by 4. That’s it, simple. [Read more…]

by Fred Schenkelberg 3 Comments

Create a Stem and Leaf Plot

There are times when you do not have a computer available and would like to visualize the distribution of a small set of data. With paper and pencil, you can create a representation that is similar to a probability density function plot. [Read more…]

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When to Make a Reliability Prediction

The easy answer is very often. Each time you want to know how long a product will operate. The accompanying question on how well the estimate will match actual performance makes the real answer more difficult.

We regularly and intuitively do reliability predictions all the time. When starting a car at the beginning of a trip, we estimate the ability of the vehicle to complete the journey. When we purchase a phone, we expect it to operate for at least two years (your expectations may differ).

During the design process, we may have formal or informal useful life expectations. It is not knowing if our decisions related to the design will fulfill the lifetime expectations that leads to the desire to know how well the resulting system will operate. We also may need to estimate warranty or maintenance costs, thus knowing what is likely to fail becomes important.

In general, knowing how long something will operate without failure provides the feedback we need to create a viable system that meets our business and customer reliability expectations.

In short, we do reliability predictions regularly to gauge is we are making good decisions. [Read more…]

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Mood’s Median Test

This nonparametric hypothesis test tests the equality of population medians. While not as powerful as the Kruskal-Wallis Test, it is useful for smaller sample sizes, when there are a few outliers or errors in the data as it focuses only on the median value. [Read more…]

by Fred Schenkelberg 1 Comment

When to Do FMEA

Failure modes and effect analysis is a tool to identify potential failures and prioritize based on severity, occurrence, and detection. I like to describe FMEA as an organized brainstorm. You probably have some experience with FMEA.

In some industries, there is a high expectation or mandate to do an FMEA study. In some industries FMEA maybe just another tool to consider using during various stages of the product or asset lifecycle.

In my opinion, FMEA should be a part of your project plan when it is likely to add value.

Value in the sense that the organization will receive an adequate benefit based on the investment to conduct the FMEA study. [Read more…]

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Building a Reliability Plan

Each product development project is different.

Different features, customers, use cases, and expectations. Let’s discuss how to build a custom reliability program that fits your specific situation.

“Insanity: doing the same thing over and over and expecting different results.”

– attributed to Albert Einstein, basically describes many organizations’ reliability project plans.

The idea that a set of activities will effectively address all of the reliability risks of a new design is too common across industries.

Why is this?

Let’s explore recognizing the current situation and which activities provide the most value.

The focus should be on creating a product that meets customer and business expectations with the lowest risk and cost.
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Optimizing Maintenance

One of the considerations when planning maintenance is the timing of the replacement of parts of the system. In some cases it makes sense to wait for the item to fail, sometimes, it makes sense to place it on an interval or set an amount of operating time, and yet in others, we can measure indicators that a replacement is necessary.

In order to make these decisions, we need data.

According to O’Connor and Kleyner (Practical Reliability Engineering, 5th Ed.), we need specific information for each part. The following list outlines the recommended information. [Read more…]