Your Reliability Engineering Professional Development Site
All articles listed in reverse chronological order.
MTBF has issues. It is commonly mis-understood and mis-used. I find it hard to interpret and use for any meaningful discussion of reliability.
The entire premise of the NoMTBF site is to encourage you to not use MTBF.
There are exhaustive writings on setting meaningful goals and metrics in the business literature. A couple of tenants seem common: [Read more…]
Reliability is an attribute of an item. The item, with its design, assembly, and use, has a finite probability of working over some duration.
We deliberately attempt to create items that meet our and our customer’s expectations concerning that probability and duration. We maintain and operate our equipment with an expectation of successful performance.
We and our customers are let down when a failure occurs. We do not enjoy the benefits of the item’s value. [Read more…]
Reliability testing to determine what will fail or when will failures occur is expensive.
Organizations invest in the development of a product and attempt through the design process to create a product that is reliable. [Read more…]
In a common definition used by engineers reliability is a probability of success. It is the chance of an item operating as expected over some duration in a given environment. In this case, we have probability as part of the definition of reliability.
Reliability in common use definition includes trustworthiness, dependability and similar definitions. It’s more than how many times your friends help you move to a new apartment, it’s a feeling or sense we have concerning our ability to count on our friends for the help.
I do not like procurement organizations.
It is like saying you don’t like lawyers. I don’t know all procurement engineers or managers, so understand my statement is a grand generalization. It’s not the people I don’t like, it’s a common behavior that I’ve witnessed countless times that I do not like.
Procurement organizations tend to look for ways to reduce cost by purchasing less expensive components or materials. This is often done with little regard to the impact on product reliability.
Why is this? And what can we do as reliability professionals to change this behavior? [Read more…]
Beyond understanding what will fail (failure mechanisms) we need to know when a system will fail. Both kinds of information can be found in a variety of sources.
Unlike the stock market where we are regularly warned that past performance does not indicate future performance; in reliability engineering past performance is the best predictor of future performance. [Read more…]
The other day a student said they are asking for failure dates, not failure rates. That is a marked improvement when requesting information for the many sources of reliability information. It is not sufficient though.
Also ask for the type of failures expected or encountered during the testing or observation. [Read more…]
Have you ever wished your organization would work together to achieve a reliable product? Not just a few individuals and a heavy reliance on the reliability team to focus on highlighting and fixing reliability issues.
Some organizations tend to react to reliability issues. Prototype testing and field returns continue to surprise the team. The worst organization fall into finding someone to blame. Better organizations set to work to understand the problem and quickly resolve the issue. Some have better ‘fire departments’ than others.
Responding quicker is not really the best way to deal with reliability. [Read more…]
We rely on data to make decisions, to reveal patterns or trends, to learn about our systems and world. Data has many forms and sources. Reliability data may provide what will fail and/or when a device will fail. [Read more…]
Is it possible to foresee all reliability issues before a product launch?
No.
I don’t think so. Can we minimize surprises from field failures?
Yes.
The number of potential failures is often unknown.
Reliability engineering has value. It can improve product reliability, increase uptime, and drive customer satisfaction, for example.
Here are a couple of stories based on real situations that resulted in significant value for the organization.
Here’s an overview of the non-parametric test to evaluate if a set of samples have the same variance. If the variances are equal they have homogeneity of variances.
Some statistical tests assume equal variances across samples, such as analysis of variance and many types of hypothesis tests. It is also assumed for statistical process control purposes to determine stability (often done with range (r chart) or standard deviation (s charts). [Read more…]
A contingency table, as in the chi-squared test of independence, reveals if two sets of data or groups are independent or not. It does not reveal the strength of the dependence. The contingency coefficient is a non-parametric measure of the association for cross-classification data. [Read more…]
“The language we use matters.” Wayne Nelson
How we talk about reliability does matter. It sets expectations and influences decisions. We talk about reliability as it is important to our customers and our business. The successful operation of the equipment in a plant permits the production of products. The successful operation of the product satisfies the needs and expectations of our customers.