Your Reliability Engineering Professional Development Site
The trite answer is just as many samples as you need and not one more.
A better answer is enough samples to make the right decision. The realistic answer is you will not enough samples.
“How many samples?” is an oft-asked question when planning for quality or reliability testing. [Read more…]
Every product and process has built into it elements that impact the safety, quality and reliability performance.
These features will always be present whether deliberately crafted or not. [Read more…]
A break from the normal format.
Reliability.fm is a podcast network focused on reliability engineering topics.
Starting with three shows. Speaking of Reliability and Dare to Know described below, along with recorded Accendo Reliability webinars. [Read more…]
My first major product design review was much less than I thought it would be. This was a new inkjet printer platform and the checkpoint review assessed the teams work and readiness to move to the next stage of development. A team of over 200 engineers and managers meet for 4 hours. [Read more…]
Failures happen. Sometimes product failures happen quickly.
You just bought a new feature rich computer and discover it doesn’t work. Right out of the box, it will not power up. Conversations with the tech support and it’s a trip back to the store.
The failures that occur early the in the life of a product tend —
this ‘tend’ really is just a vague ‘in general’
…tend to occur because of manufacturing errors or shipping/installation damage.
Not always, though. [Read more…]
First off, switches are not perfect, so this situation includes the reliability of the switch. Switch reliability may be a factor of storage time, probability of actually working when called on to work, or number of switching cycles. Each switch technology may be slightly different. For this equation, you need the reliability or probability of success given the primary unit has failed. Although we are assume the switch reliability is independent of the primary unit reliability and subsequent failure.
[Read more…]
Selecting as a supplier for components or subsystems involves many aspects including the desired reliability performance.
Once selected the ability of the supplier to provide items that meet or exceed the reliability requirements relies on their understanding of the requirements and operational conditions related to the specific item within the system.
It also relies on the supplier’s knowledge of their own design and manufacturing processes as it related to the reliability performance.
This is not the same as a confidence interval. For a mean or standard deviation, we can calculate the likelihood that the true parameter is within a range of values — confidence interval concerning a parameter.
A tolerance interval applies to the individual readings, not the statistics. The interval contains a certain proportion of the values within the distribution of individual data points. The endpoints are tolerance limits. [Read more…]
Your customers are your best testers for your next product. They will explore the features. Expose the product to use conditions in unconscious ways. And, they will let you what they consider failures without needing the specification document.
During the development process, you and team may work to understand what customer may want or expect for the new product. You may even conduct focus groups or review past product field failures and call center records. [Read more…]
First off, switches are not perfect, so this situation is hypothetical. Yet, when you are exploring adding standby redundancy and haven’t sorted out the switching mechanism, you may be purely curious about the benefits of the redundancy. [Read more…]
Mechanical systems wear out and fail eventually. The ability of a structure to support a load, move through the specified range of motion, or spin degrades with use and time. Even our joints eventually wear out.
Accelerated life testing (ALT) has plenty of literature concerning the failure mechanisms unique to electronic components and materials. This is partially due to the limited number of unique electronic components compared to the often custom mechanical designs. ALT also has value as it provides information about a system’s reliability performance in the future.
Let’s explore an example of mechanical reliability testing (an ALT) in order to outline a basic approach to ALT design and analysis. [Read more…]
Most statistics books and the CRE Primer have tables that permit you to avoid calculating the probability for common distributions. The normal distribution requires numerical methods to conduct the calculations and would not be feasible during the CRE exam. [Read more…]
Suppliers often include reliability information along with performance specifications.
We look for reliability statements as one part of the selection process to ascertain if the component is likely to have sufficient reliability.
When the vendor’s data is clearly stated and meaningful, that information saves us from potentially having to conduct our own reliability evaluations. [Read more…]
There are a number of different methods to calculate confidence intervals for a proportion. The normal approximation method is easy to use and is appropriate in most cases.
Clopper and Pearson describe the Clopper-Pearson method also called the exact confidence interval and we’ll describe it in a separate article.
There are other methods, which again will find a description in separate articles. [Read more…]
If you buy more than one of an item used in your product, you will have to deal with variability. In general, the variability from part to part is minimal and expected. Occasionally, the variability is large and causes reliability problems. [Read more…]