Your Reliability Engineering Professional Development Site
There are two common uses for a check sheet. First, to summarize historical data, or second, to collect observations. A byproduct of creating a check sheet is team agreement on definitions of categories and observation procedures.
The investment is minimal other than thinking about how you want to view the data, and what data to collect. [Read more…]
When you have a scattering of ideas or suggestions, you can use affinity diagrams to organize and group them.
Affinity diagraming is a simple way for an individual or (better) a group to quickly gather and organize a large number of disparate concepts, ideas, suggestions, etc. It is a natural activity after a brainstorming session. [Read more…]
Jezdimir Knezevic of the MIRCE Akademy published a paper with the title above and I have a few comments.
In the article, Jezdimir suggests that the statistical approach to describing the world about us is fundamental flaws and not inherently useful for our use. He compares a mathematical/statistical approach to a scientific approach and finds the stats wanting.
Let’s take a critical look at the topic of this paper and conclusions. [Read more…]
Did you know that best idea to solve a problem is often not the first one?
We all have plenty of bad ideas, hunches, guesses, and flawed ideas. That is ok. We also have great ideas and elegant solutions, too. The trick is exploring all those ideas to find the best ones.
One technique to draw out and capture many ideas is called brainstorming. You most likely have heard of and used this tool already. Let’s review a few key elements that make for excellent brainstorming results. [Read more…]
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Stay informed on the latest content added to the site, including: articles, podcasts, webinars, live events and assorted other reliability engineering professional development materials added each week.
The Friedman test is a non-parametric test used to test for differences between groups when the dependent variable is at least ordinal (could be continuous). The Friedman test is the non-parametric alternative to the one-way ANOVA with repeated measures (or the complete block design and a special case of the Durbin test). If the data is significantly different than normally distributed this becomes the preferred test over using an ANOVA.
The test procedure ranks each row (block) together, then considers the values of ranks by columns. The data is organized in to a matrix with B rows (blocks) and T columns (treatments) with a single operation in each cell of the matrix. [Read more…]
Systems and processes exist in our dynamic world. Each organization and situation is different. Just as there is not one risk management process that works for any organization, there also is the need for continuous improvement of an existing system.
When first designing a risk management process for your organization, you consider your objectives and adjust a framework to fit your needs. Over time your objectives and the surrounding environment changes, thus requiring a critical look at your process. [Read more…]
Let’s say you have shipped 1,000 products to your customer on January 1st. All are immediately placed into service. And each month since you have received a few product returns, what we are going to call failures. We also have fitted the data to a Weibull distribution. Then in May, your boss asks you to estimate how many failures to expect in June.
This is a simple example as we’re not shipping units every month, nor changing the product design or assembly process. We also have worked out the fitted Weibull parameters already. That leaves the calculation of how many failures we should expect over the next month. [Read more…]
I like to say Reliability is all of quality over time. Quality professional tend to say reliability is an element of quality. David A. Garvin of the Harvard Business School suggests there are eight dimensions to quality, including reliability.
Either way one relates quality and reliability we need to remember that quality or reliability is not a department, team, the engineering down the hall. Quality and reliability is part of the culture of the organization. It is how we make decisions the impact how the product or service performs for customers. [Read more…]
“How many samples do we need?” is a very common question. It is one you will receive when planning nearly any kind of reliability testing. It is a great question.
Having too few samples means the results are likely not useful to make a decision. Too many samples improve the results, yet does add unnecessary costs. Getting the right sample size is an exercise starting in statistics and ending with a balance of constraints.
There are six elements to consider when estimating sample size. We will use the success testing formula, a life test with no planned failures, to outline the necessary considerations. [Read more…]
We can plan to do more than we are capable of accomplishing. The remaining items, if they warranty accomplishing become deferred. They roll over to the next’s day’s list of actions to take.
Of course, in practice, the process to plan, execute, and defer maintenance activities is a bit more complex than described above. The ability to maintain equipment in working order along with minimizing downtime and costs is in large part the balance between resources available to conduct maintenance and the increased risk of system failure due to deferred maintenance. [Read more…]
When looking at a pile of data, sometimes there is a data point that is not like the others. It attracts attention as it is different than the rest of the data.
When I spot something odd in a dataset, I wonder if there is something to learn here. Is this an opportunity to make a discovery or improve a process?
All too often it is tempting to remove the outlier as a mistake. Or to drop the outlier as it doesn’t make any sense and ‘messes up’ the analysis. [Read more…]
A risk management plan has to meet your organizations needs as the organization identifies, manages, and mitigates potential and actual risks. The ISO 31000 framework does not detail how an organization should plan or what elements are required for an effective plan.
This short article outlines a few details that may comprise a starting point as you build a risk management plan within your organization. Or, the suggestions here may help you review and improve your existing plan. [Read more…]
The McNemar test is a nonparametric statistical test to compare dichotomous (unique) results of paired data.
If you are comparing survey results (favorable/unfavorable) for a group of potential customers given two ad campaigns, or evaluating the performance of two vendors in a set of prototype units, or determining if a maintenance procedure is effective for a set of equipment, this test permits the detection of changes.
The McNemar test is similar to the χ2 test. The McNemar only works with a two by two table, where the χ2 test works with larger tables. The χ2 test is checking for independence, while the McNemar test is looking for consistency in results.
Let’s examine an example where a group of people are surveyed about a prototype design, before and after a presentation. [Read more…]
Kishor forward the link to the recording to me and suggest it may of interest to the Accendo Reliability community. I agree. He does a great job discussing the topic and a clear and practical manner.
The video abstract is:
IEEE Life Fellow and Hudson Chair in the Department of Electrical and Computer Engineering at Duke University Prof. Kishor S. Trivedi visited Alibaba’s Hangzhou campus on Dec. 8th and talked about technical systems’ reliability and availability assurance methods based on probabilistic models. [Read more…]