Your Reliability Engineering Professional Development Site
All articles listed in reverse chronological order.
Tim Rodgers interviews Fred Schenkelberg, consultant and blogger of NoMTBF, concerning Fred’s work and writing around the perils of MTBF.
We range from what started the site and the common issues caused by using MTBF. Then we discuss using reliability instead.
The ASQ CRE exam is difficult. The individual elements of the body of knowledge are not in themselves difficult, it is just such a broad range of topics that mastering all the subjects is a challenge.
The CRE Body of Knowledge includes elements of leadership & management, testing & failure analysis, and basic & advanced & reliability statistics. Reliability engineers work across the spectrum of consumer product design to plant maintenance.
Depending on your experience you may have a wealth of experience with availability modeling and repairable system data analysis, and have little experience with design for reliability practices. [Read more…]
Reliability goals provide you and your team a focus for the reliability program. They provide a measurable way to design, test, and maintain systems that meet customer expectations.
A goal of any kind in a business is relatively easy to set and publish. They are not easy to entwine into the culture of the organization so the objectives desired by achieving the goal become a meaningful focus. A product development team may have hundreds of pages of specifications and a long list of priorities and objectives. Simple listing a reliability goal, no matter how clearly stated, may not be sufficient to garner the interest of your team.
Simple listing a reliability goal, no matter how clearly stated, may not be sufficient to garner the interest of your team.
Common mode or common cause failures related to redundant systems where one cause can lead to the failure of otherwise redundant elements leading to system failure.
Elements which should fail independently are under some circumstances dependent.
When considering the probability of individual paths in a complex redundant system, take due care to consider the common mode failures which may have a higher probability than any single path in the system. [Read more…]
Reliability engineering is a blend of disciplines from material science to asset management. We use problem-solving, design, maintenance, and statistical tools on a regular basis, yet that is not the only thing we do.
Having met a few engineers that define their role as a reliability engineer as conducting HALT or FMEA only, strikes me as to what most believe we do, or should do, as a reliability engineer. It is true that someone may specialize by choice or chance on one tool, yet even then is that all they do?
I don’t think so.
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…]
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.
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…]
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…]
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…]
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.
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…]
Over the past two weeks this site has received over 150 visitors each weekday. From what I can see in the analytics and from a few conversations with folks, the site provides insights and information around the use of MTBF, plus basic information concerning reliability engineering.
Google tends to like the site as they agree that visitors like the site, too.
Given the interest and plenty of encouragement (and helpful suggestions) I’m putting together a book based on the NoMTBF material. Not just bashing MTBF, although there is plenty of that, but also the steps to use reliability or other measure that provide better information.
I have the basic outline and draft completed and am now ready for some feedback. If you’d like to review the work, conditional on you providing you feedback, suggestions, ideas and comments, let me know and I’ll send you a draft copy.
The draft needs work on formatting, layout, adding clean graphics, etc. Yet the outline and basic text is there.
Can you follow the argument, is the writing clear, is there anything missing, how about the order or emphasis?
It’s not a long work, right now about 22,000 words or depending on book page size, fonts size, margins, etc. about 100 to 120 pages. In word it has 73 pages right now without any attention to formatting.
If you have the time and interest let me know and I’ll send you copy, but you have to comment, critic, and make suggestions. I really would like this work to be useful for you and for use to encourage others to avoid using MTBF.
This period of reflection concerning the NoMTBF project has reinforced the idea that we need to provide something concrete and positive to do instead of just not doing MTBF. Part of the issue is our education system, standards, and textbooks as they often include MTBF in examples and at length in the discussion.
So, the idea is to create a course for experienced reliability professionals and interested engineers and managers with an interest in reliability, that focuses on reliability metrics from goal setting to tracking performance.
I’ve the technology to put together an online course that could be self paced or provided on a fixed schedule (say weekly). It could include short lectures, discussions, reading material and quizzes or examples to work.
Here’s a draft outline – what do you think?
Common reliability measures: pros and cons
Reliability and Availability Goal setting – connecting the goal to your business objectives
Estimating reliability for comparison to the goals
Tracking reliability and reporting performance
Reliability testing with results that compare to goals
Reliability modeling that leads to meaningful discussions and decisions
Common mistakes and remedies concerning reliability measures
How to get useful reliability information from vendors
(plenty of opportunity for bashing MTBF, yet if done in contrast to much better methods and measures, may provide really practical and useful information.)
So, thoughts? What would you want added, emphasized, and what would you want to be main take aways for each topics? What would you like to see in the course for yourself or for those you’d recommend take the course?
If you’d like to participate in the course project, I’m very open to your ideas and suggestions. Maybe help create and present a topic, provide examples, or sample problems or discussion questions.
Anyway, looking for feedback and ideas to make the NoMTBF site much more positive and useful for the reliability engineering community and for anyone interested in reliability.
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…]
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…]