Your Reliability Engineering Professional Development Site
All articles listed in reverse chronological order.
This is also called the “p test”
When comparing proportions that are from a population with a fixed number of independent trials and each trial has a constant probability of one or another outcome (Bernoulli experiments) then we can use a p test. p is the probability of success, and 1-p is the probability of failure. Caution: stay consistent once you define success otherwise, like me, you’ll have a bit of confusion. n is the number of trials. [Read more…]
The target, objective, mission or goal is the statement that provides a design team with focus and direction. A well-stated goal will establish the business connection to the technical decisions, related to product durability expectations. A well-stated goal provides clarity across the organization and permits a common language for discussing design, supply chain, and manufacturing decisions.
Let’s explore the definition of a ‘well-stated reliability goal.’ First, is it not simple MTBF, “as good as or better than…” or ‘a 5-year product’. These are common ‘goals’ found across many industries, yet none permit a clear technical understanding of the durability expectations for the product.
The common definition for reliability is [Read more…]
The design of a product includes the arrangement of all of the product elements. When considering the reliability of a system, the arrangement matters. Many systems are arranged serially. This means that with the failure of any one element, the system will not work. See the article on Series Systems for more details. [Read more…]
It’s always necessary to estimate the value of specific reliability activities. It is needed to justify the investment required to accomplish the task. Prototypes, diagnostics equipment, and environmental chambers are expensive. The difficulty is an inability to know what will be found, before conducting the experiment.
Not doing the test means the certainty of not finding anything. That is often not enough motivation to invest, to learn something about the reliability performance. The following scenario is just one situation, along with a few ideas to help you estimate the value of investments in reliability work. [Read more…]
The mean time between failure (MTBF) is arguably the most prolific metric in the field of reliability engineering. The MTBF is used as a metric throughout a product’s life-cycle; from requirements, to validation, to operational assessment. Unfortunately, MTBF alone doesn’t tell us too much. [Read more…]
Design of Experiments (DoE) and the Analysis of Variance (ANOVA) techniques are economical and powerful methods for determining the statistically significant effects and interactions in multivariable situations. DoE may be utilized for optimizing product designs, as well as for addressing quality and reliability deficiencies. Within the DoE framework, the practitioner may explore the effects of a single variable or analyze multiple variables. [Read more…]
The Failure Reporting and Corrective Action System (FRACAS) is a closed-loop process whose purpose is to provide a systematic way to report, organize and analyze failure data. Implementation of a FRACAS has increasingly become commonplace within an industry. The requirement for implementation of some type of FRACAS within a DoD program was first established in 1985 with MIL-STD-2155. However, in 1995 that standard was reestablished with no changes to content as a handbook, MIL-HDBK-2155, and was recommended as guidance. Today, multiple software solutions exist that provide all the functionality required of a FRACAS. [Read more…]
After the system has been drawn in block diagram form, subsystem and component reliability goals and targets are established. This is a common practice in the development of complex systems, particularly when different design teams or subcontractors are involved. Reliability allocation involves setting reliability objectives for components or subsystems in order to meet a system reliability objective and should occur in the initial stages of design or prior to designing major system upgrades. [Read more…]
Creating a product or maintaining equipment is actually about our ability to manage risk. The various risks are outlined below, and there are more to consider. This summary covers the basics related to reliability. [Read more…]
This example is based on a real situation. After a class on design for reliability, a senior manager declared that every component would be fully derated in every product (electronic test & measurement devices). Within a year the design team redesigned all new and existing products, with strict adherence to the derating guidelines provided in the class. A year after the class the product line enjoyed a 50% reduction in warranty claims. They learned about derating and a manager saw the potential value. [Read more…]
This is a two part series where I outline the basic elements of creating and supporting a reliability program. [Read more…]
Here is an example of how to determine the future value of a specific reliability task. Many of us face the challenge of how to justify spending product development resources to provide insights and information to the rest of the team. Accelerated life testing (ALT) is particularly difficult: It is time consuming, expensive, and at times statistically complex. Having a clear method to estimate the value serves your career and the organization well, as both benefit from the right investments.
In the NoMTBF newsletter I’ve announced a contest for this site.
I’d like to invite you to write a guest post on MTBF, either good or bad, for or against, a case study or how-to-use article. Just something about MTBF.
Then, if during the week we post it the site reaches a new record for visits, I’ll send you a shiny new NoMTBF logo coffee mug. [Read more…]
A recent forum post included the notion that many engineers and managers developing products or maintaining equipment have knowledge apathy concerning reliability. “They don’t care!” was the poster’s words. Has this happened? Have we lost the ability to care about reliability?
In a course I teach on reliability engineering management I ask my students to find an advertisement using reliability as a central theme or claim. This isn’t very hard to do, and I’ve regularly been surprised at the range of uses advertising finds around the concept of reliability. ‘Reliable Movers’ claims to reliably and safely move your belongings to your new home. A reliable shotgun ammunition-loading device suggests each shell will fire reliably. And, many other advertisements use the basic concepts of consistent, repeatable, safety, and trustworthy via the term reliable or reliability. There is a common and good association with reliability. [Read more…]