Your Reliability Engineering Professional Development Site
MTBF use and thinking is still rampant. It affects how our peers and colleagues approach solving problems.
There is a full range of problems that come from using MTBF, yet how do you spot the signs of MTBF thinking even when MTBF is not mentioned? Let’s explore the approaches that you can use to ferret out MTBF thinking and move your organization toward making informed decisions concerning reliability. [Read more…]
Over 20 years ago the Assistant Secretary of the Army directed the Army to not use MIL HBK 217 in a request for proposals, even for guidance. Exceptions, by waiver only.
217 is still around and routinely called out. That is a lot of waivers.
Why is 217 and other parts count database prediction packages still in use? Let’s explore the memo a bit more, plus ponder what is maintaining the popularity of 217 and ilk.
[Read more…]
Ongoing Reliability Testing (ORT) is a class of product testing that aims to identify potential field reliability issues after product launch and before customers experience failures. Typically, done using a rotation of samples directly from production and using expected use conditions/stresses, the testing balances many factors to be of value.
ORT works well to monitor an ongoing production process subject to variation. If that variation impacts reliable performance, then a well-designed and implemented ORT should identify the issue.
Let’s explore the range of considerations when designing an ORT to optimize the ORT’s ability to identify field problems efficiently. We will also discuss the various tradeoffs that impact sample size, the use of accelerating stresses, and more.
At least one group called this the ‘Delta Phase.’ It is the period shortly after launching a product and provides a unique opportunity to reduce future field failures and improve customer satisfaction dramatically. The idea is to aggressively identify and resolve any field issues identified by your customers.
There are a couple of ways to implement the Delta Phase with your product launch. Yet, it requires creating a team from the design/development team that has the authority and capability to implement design changes quickly.
Let’s explore the concept of a delta phase and how to implement it in your organization. Plus, let’s examine a few situations that make significant short and long-term reductions in the field failure rate.
This is a question someone posted to Quora and the system prompted me to answer it, which I did.
This question is part of the general question around which software tools do you use for specific situations. First, my response to the question. [Read more…]
System or Operational Effectiveness is comprised of three elements. An early definition included capability, reliability, and availability. Another early definition included availability, dependability, and capability. In essence, can the system do what it’s supposed to do? Is it ready when needed? And is it able to work without failure long enough?
Let’s examine system effectiveness and its factors or elements in more detail. Then, examine an example or two so you can apply this concept to your situation.
Let’s say we want to characterize the reliability performance of a vendor’s device. We’re considering including the device within our system, if and only if, it will survive 5 years reasonably well.
The vendor’s data sheet lists an MTBF value of 200,000 hours. A call to the vendor and search of their site doesn’t reveal any additional reliability information. MTBF is all we have.
We don’t trust it. Which is wise.
Now we want to run an ALT to estimate a time to failure distribution for the device. The intent is to use an acceleration model to accelerate the testing and a time to failure model to adjust to our various expected use conditions.
Given the device, a small interface module with a few buttons, electronics, a display and enclosure, and the data sheet with MTBF, how can we design a meaningful ALT? [Read more…]
Thanks to a reader that noticed my question on why MTBF came into existence, we have a new (new to me at least) rationale for using MTBF. Basically, MTBF provides clarity on the magnitude of a number, because a number in scientific notation is potentially confusing.
What is doubly concerning is the use of MTTF failure rate values in ISO standards dealing with system safety.
Let’s explore the brief email exchange and my thoughts. [Read more…]
Goals, objectives, milestones, targets, whatever you call them, just have a clear one. Setting a reliability goal is easy. Get a few people together for a short discussion and in less then 10 minutes you can craft a meaningful reliability goal.
Let’s explore the elements that make up a reliability goal. Plus, the range of inputs you can use to define each element. Plus, some best practices when establishing goals.
Finally, simply setting a goal adds value to your organization – if it is a complete and practical goal. Estimating or measuring that value can be tricky, so let’s discuss a few ways you may quantify the value of a goal.
Guest post by Msc Teofilo Cortizo
The term MTBF (Mean Time Between Failures) within maintenance management, it is the most important KPI after Physical Availability. Unlike MTTF (Mean Time To Failure), which relates directly to available equipment time, MTBF also adds up the time spent inside a repair. That is, it starts its count from a certain failure and only stops its counter when this fault was remedied, started and repeated itself again. According to ISO 12849: 2013, this indicator can only be used for repairable equipment, and MTTF is the equivalent of non-repairable equipment. [Read more…]
Reliability activities serve one purpose: to support better decision making.
That is all it does. Reliability work may reveal design weaknesses, which we can decide to address. Reliability work may estimate the longevity of a device, allowing decisions when compared to objectives for reliability.
Creating a report that no one reads is not the purpose of reliability. Running a test or analysis to simply ‘do reliability’ is not helpful to anyone. Anything with MTBF involved … well, you know how I feel about that. [Read more…]
Three prototypes survive the gauntlet of stresses and none fail. That is great news, or is it? No failure testing is what I call success testing.
We often want to create a design that is successful, therefore enjoying successful testing results, I.e. No failures means we are successful, right?
Another aspect of success testing is in pass/fail type testing we can minimize the sample size by planning for all prototypes passing the test. If we plan on running the test till we have a failure or two, we need more samples. While it improves the statistics of the results, we have to spend more to achieve the results. We nearly always have limited resources for testing.
Let’s take a closer look at success testing and some of the issues you should consider before planning your next success test. [Read more…]
The following note and question appear in my email the other day. I had given the definition of reliability quite a bit of thought, yet have not really thought too much about a definition of ‘product life time’.
So after answering Najib’s question I thought it may make a good conversation starter here. Give it a quite read, and add how you would answer the questions Najib poses. [Read more…]
Professional development is not about pursuing a degree or title. It’s about what you can do with your knowledge. Of course, that is my opinion. Some seek credentials that may lead to a new position or opportunities. Some seek knowledge without intending to use it – education for education’s sake.
Whatever the motivation, we should approach learning meaningfully. Set objectives, do the homework, get feedback or coaching, and establish a routine to continue to hone your knowledge. Whether you want to learn something out of curiosity or master a topic to accomplish a task, you can plan to use your time efficiently.
Let’s explore how to improve your ability to learn and continue to learn throughout your career. As reliability engineers, there seems to be a never-ending list of concepts, failure mechanisms, novel materials, etc., that we can and should know about. With so many options for professional development, let’s examine a few principles and tips so you can learn and master what you desire to learn and master.
Here’s a common problem: You have been tasked with peering into the future to predict when the next failure will occur.
Predictions are tough.
One way to approach this problem is to analyze the history of failures of the most typical system. The issue looms larger when you have only two observed failures from the population of systems in question.
While you can fit a straight line to two failures and account for all the systems that operated without failure, it is not very satisfactory. It is at best a crude estimate.
Let’s not consider calculating MTBF. That would not provide useful information as regular readers already know. So what can you do given just two failures to create a meaningful estimate of future failures? Let’s explore a couple of options. [Read more…]
