Your Reliability Engineering Professional Development Site
What Does ‘Lifetime’ as a Metric MeanWe talk about lifetimes of plants and animals. Also, you may talk about the lifetime of a product or system.
I expect to have safe and trouble free use of my car over its lifetime. Once in a while I find a warranty that says it is guaranteed over my lifetime — for as long as I own the blender, for example. [Read more…]
Time to Update Our StandardsNot our personal or moral standards, rather the set of documents we rely upon as a foundation for reliability engineering tools and techniques.
We have a wide array of standards for reporting reliability test data to calculating confidence intervals on field returns. We have standards that describe various environmental conditions and appropriate testing levels suitable to evaluate your product. We define terms, concepts, processes, and techniques.
Despite the many documents and impressive titles of numbers and abbreviations or acronyms, most of the standard related to reliability engineer fail to include sufficient context and rationale concerning when and why to use or modify the standard. If a specific test is to determine the expected lifetime of solder joints, well, which type of solder joints (shape, size, configuration, material, and process) is the standard appropriate and when does it not apply? Make the boundaries of applicability clear.
No single test works for all situations.
For example, a wrist watch standard defining how to test for specific water resistance claims does not evaluate the effects of corrosion. The standard has the watch or similar device exposed to a set of water conditions, then evaluate if the system is operating, nearly immediately after the water exposure.
We know that water encourages corrosion, yet takes time to occur. Water alone on a circuit board is no big deal (much of the time) it’s when the water facilitates the creation of additional and unwanted current paths that there is a problem. Metal migration and rusting, take time to occur.
If the standard for water resistance doesn’t evaluate corrosion, and it’s one of the ways your product fails, too bad. You can ‘pass’ the test, meet the standard, add it to your data sheet, and the customer will still experience a failure.
Same for many environmental testing, FMEA, life testing, field data analysis, and a range of other standards. They do not include the critical information necessary for appropriate application of the standard to your particular situation.
Many, not all, standards provide a recipe to accomplish as task or evaluation. One of the values of the standard is different teams may replicate the results of one team by repeating the steps outlined in the standard.
One of issues with standards is they do not include how and why to actually accomplish the set of tasks and what to do with the results. In part, we need to clearly connect, say the task of testing a product across a range of temperature and humidity conditions, only if it will provide meaningful information.
Don’t run the test if the information is not needed, unnecessary or meaningless.
For example, if we expect that exposure to high temperature and humid conditions may increase the chance of product failure. We may want to know
Or any number of reasons to use the results of the testing. Often we run a standard test with very few samples, experience no failures and erroneously conclude all it good. Then surprised that failures occur anyway when the product is in use.
The standard let us down.
The standard provided only a recipe or outline for a procedure and now that guidance and rationale on how it may or may not help us and our team resolve very real questions. Testing 3 units that all pass does not mean your solar panel will survive hot and humid conditions for 20 years with no failures. It doesn’t.
Only run the test or work to accomplish a process only if it is tied to answering a question. Focus on business decisions and the questions we have to resolve in order to make better decisions (i.e. Wrong less often).
Let’s change the way we read and use standards. You may need to add the how and why, the boundaries, and the connection to value for your situation. It’s not always easy. The people writing the standard often have sufficient experience to include guidelines to help you — when possible contact them and ask what was their thinking and what are the limitations.
If enough of us avoid simply meeting the requirements of the standard, we will
Hiding From Your Field Data Reality?One of the major dilemmas of reliability engineering is one we really need to solve. Too many times we are trapped by our organizations competing priorities and working with inadequate information.
We generally understand that field failure data provides the best possible representation of our product’s reliability performance. It’s data from our population of products with our customers while they apply all the stresses’ customer will apply to our product. Customer’s report the failures they care about, and not failures of little significance. [Read more…]
When Your Supplier Converts Reliability to MTBFOh, the trouble that will occur. The mistakes, mishaps and errors and most certainly the inability of the supplier to provide a reliability solution.
If you provide the supplier with a straightforward and complete reliability goal, and they convert it to an single number as an MTBF value, what really could go wrong? Also, why would the supplier degrade the requirement to an MTBF value? [Read more…]
What is MTBF?The acronym MTBF is commonly known in our field as Mean Time Between Failure.
It is also associated with repairable systems in most text books.
It is also denoted as the theta parameter for an exponential distribution.
It is referenced as a metric for reliability, too. Oh, and it is the inverse of the failure rate.
And, it is mis-understood and mis-used by many. I digress, as there is plenty already written on the perils of MTBF.
What is MTBF? And where and how should it be used, if at all? [Read more…]
First off I want to say thanks to you the readers of the NoMTBF blog. The notes of thanks, of encouragement, and support all propel me to write to you each week.
I especially like the stories of success helping someone ‘get it’ concerning the common misunderstandings of MTBF. I have to think your work and actions is making a difference across the field of reliability engineering. We’re making progress. [Read more…]
Predicting Failure vs. Reacting to FailureOne of the twitter notes I sent out a few weeks ago in part read, “Celebrate failures”. And a comment came back that it was a wonderful approach that she had not though of before. Failure will occur and when it does it is our chance to learn.
And, we need to learn. As reliability professionals, we continue to learn our entire career. New materials fail in novel manners. New assemblies fail in an assortment of ways. New designs fail due to unknown sources of variation. We will see failures. So rather than simply focus on the next try and hope to find success, let’s learn from each failure as we move toward success. [Read more…]
Reliability Testing with ConstraintsIn some cases we have to conduct testing and are asked to not break the product. Now, that isn’t all that fun as a reliability engineer. We want to find what fails and understand it. Or, we want to confirm what we expect will fail, actually does as expected.
So, what do we do when confronted with a very small sample size (that is one issue) and are expected to conduct failure free testing (second issue)? Let’s explore each issue separately and come up with a few suggestions on how to proceed.
Thanks to Олег (@OlegV_Ivanov) via Twitter for the article suggestion. Thanks for the idea Олеr. [Read more…]
The Impact of IoT on Reliability EngineeringArticle inspired by @JillNewberg thanks for the suggestion Jill.
There are two elements to this subject. First there is the reliability of the elements collecting and connecting to the internet. Second is the potential value of the connection and information. [Read more…]
As reliability engineers we are the local expert. We know the arcane arts of product life and equipment uptime design and maintenance. We are sought after to estimate useful life, time to first failure, and consulted when failures occur. [Read more…]
Take Action Today to Improve How Your Organization Talks About ReliabilityYou know the perils of MTBF use. The widespread misunderstanding and mis-use. You know about how MTBF treats your data poorly.
You also know everyone around you uses MTBF. Your industry uses MTBF. And, now one likes change, least of all about metrics concerning reliability.
As I said to a friend this morning, “The madness has to stop.”
And, you feel that say way. So, what are you going to do about it? Here are five things you can do today.
Encourage five of your colleagues to check out and subscribe to this site, www.nomtbf.com.
Ask a vendor how they determined the MTBF value they are presenting on the data sheet? What evidence supports that claim and what assumptions are included (often unstated)?
The next time you hear someone mention MTBF, ask them what do they mean? And, than ask what percentage of items should survive a year? If they are not consistent — you found a learning opportunity.
Write a blog post for the www.nomtbf.com site. What have you done to encourage better understanding of reliability concepts in your world? Share you hints, tips, stories, and advice here.
Pick one for today and do as many as you can. What would you add to this list? What kind responses are you receiving when you speak out about the perils of MTBF.
Keep up the effort. Together we are making progress. Thanks for the support.
How to Translate Customer Expectations About ReliabilityAs a customer when I purchase a new car, a toaster, or a pump for my production line, I expect it to work. To Just Work. As a reliability professional, I also have the language to specify what I mean by, ‘just work’.
Customers that are not reliability engineers do not accurately specify what they mean by ‘it should just work’. So, we have to do a little extra to help translate that they want into specifications that we (manufacturer of the item) can create and deliver. [Read more…]
I endured a difficult conversation with a project manager yesterday. The meeting agenda included an initial discussion about the product development reliability plan. She agreed that we needed to identify risks and provide feedback to the team concerning product reliability. [Read more…]
MTBFMean time between failure or mean time before failure is very common. The common definition describes MTBF as a reliability measure that is calculated by tallying operating hours and dividing by the number of failures. Intuitively this is the average time until a failure occurs. Mathematically it is the inverse of the failure rate. Generally used for repairable systems. [Read more…]
What is Reliability?It’s not MTBF. It’s not just the period of time the product does not fail. It’s not just a probability.
It’s a bit more. Reliability is it ‘just works’.
HP calculators are reliable. They work and keep on working. Apparently Lexus makes reliable cars. (According to the current car rankings by Consumer Reports, 2015). My coffee maker is reliable.
The dictionary on my Mac says reliable is:
And, according to O’Connor and Kleyner in Practical Reliability Engineering, 5th ed. Reliability is:
The probability that an item will perform a required function without failure under stated conditions for a stated period of time.
This is a definition we can use as engineers. It has four parts:
And we certainly can define and measure each well.
BTW: MTBF is only probability (actually stated as an inverse failure rate), thus does not fully define reliability.
Consistent, trustworthy? Yes, a reliable product or system should process these essential qualities, too.
Reliability conjures many images and thoughts. The examples you envision are different than mine. That is fine. The concept remains the same. When an item is reliable, it just works. I like to add that it just keeps on working.
When setting goals, estimating, predicting, or measuring reliability, use all four element of the definition laid out by O’Connor and Kleyner. Be clear and complete. Keep it simple and make it reliable.
What comes to mind when you think of reliability? Leave a comment and share what you consider reliable.