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Prep notes for ASQ Certified Reliability Engineer exam ISSN 2165-8633
The CRE Preparation Notes series provides you with short practical tutorials on all the elements that make up the ASQ CRE body of knowledge. The articles provide introductory material, basics, how-tos, examples, and practical use guidance for the full range of reliability engineering concepts, terms, tools, and practices.
Keep your knowledge fresh by regularly reviewing topics and tools that make up reliability engineering.
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You will find the most recent tutorials in reverse chronological order below.
Becoming an ASQ CRE is one milestone in your career. It involved gathering experience and studying the broad reliability engineering body of knowledge.
It also involved an ongoing application of what you know and learn. I’ve found being a reliability engineer involves learning about materials, designs, systems, people, and tools & techniques. Mastery takes time and a good library. [Read more…]
Embarking on a product development project contains many aspirations, including that the product should work as expected.
The device functions and does so over time. Enough time for the customer to deem the device reliable.
That is one way to approach setting a reliability goal for a project. Estimate what will delight the customer. Set a target for how long without failure your new design function.
The goal provides a focus for the team. [Read more…]
A common question concerns the warranty period.
How long should we, the manufacture guarantee that our product will work as expected? Do we include limitations or not? How do we decide? [Read more…]
Here’s a short list of terms related to warranty management. Often is the words we use that matter and understanding the language of warranties is one step in mastering warranty management.
A promise made to the buyer of an item that the manufacturer (seller) will repair or replace the item if necessary within a specific time period. [Read more…]
When making a transaction there is an element of trust.
The buyer is trusting you are providing a product that lives up to the claims provided. Neither party wishes to be duped. Yet, we do enter into transactions. We buy stuff.
A few hundred years ago and prior most purchases were from someone you knew, and most likely knew well. It was in the craftsman’s best interest to maintain honest dealing and create quality products. If not, they would enjoy less business. [Read more…]
In many parts of the world ‘caveat emptor’ [let the buyer beware] no longer applies.
The producer and distributors of products are liable for their products.
This extends beyond product failures and a warranty claim. Today the company is liable for to make right any loss or damage incurred by the use of the product.
Courts and laws around the world reflect the protection of users of products from adverse consequences due to a negligent design and assembly practices.
The producer of a product must consider the user’s safety and provide reasonable safeguards.
This applies even when the user misuses or abuses a product. [Read more…]
The operating characteristic curve, OC curve, visualizes a sampling plan.
At times, we select a sample from a group of items and evaluate them. Does this lot of widgets meet the specifications? Does this batch measure up? [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…]
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…]
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…]
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…]
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…]
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…]
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…]
As with other point estimates, we often want to calculate the confidence interval about the estimate. The intent is to determine the range of reasonable values for the true and unknown population parameter. For MTBF, this no different.