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CRE Exam Preparation

CRE Exam Preparation

I never did like taking final exams in college as I viewed them as four hours I would rather spend doing something (anything) else. An exam is a check of what you know about a topic or subject. We prepared for those exams by reading, studying, practicing working problems (doing homework) and trying to understand the key concepts, trends, themes, etc. Some of my classmates thought it was about how much they could stuff into short term memory, others though sleep deprivation had something to do with preparing for an exam. [Read more…]

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Why HALT is a methodology, not equipment

Kirk Gray, Accelerated Reliability Solutions, L.L.C.

It is easy to understand why the term HALT (Highly Accelerated Life Test) is so tightly couple to the equipment called “HALT chambers” systems.  Many do not think they can do HALT processes without a “HALT Chamber”. Many know that Dr. Gregg Hobbs, who coined the term HALT and also HASS (Highly Accelerated Stress Screens), spent much of his life promoting the techniques and was also the founder of two “HALT/HASS” environmental chamber companies. [Read more…]

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Sample Size Problem

Sample Size Problem

Let’s work a sample size problem.

A random sample size, n, is to be taken from a large population having a standard deviation of 1″. The sample size is to be determined so that there well be a 0.05 risk probability of exceeding a 0.1″ tolerance error in using the sample mean to estimate μ. Which of the following values is nearest the required sample size?

a. 42

b. 106

c. 203

d. 384 [Read more…]

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Websites for Reliability

note: if you know of a great online resource that isn’t on this list, please add a comments and we’ll add it to the list for all to share.

Shon Isenhour recently posted on Linkedin a question about online resources helpful for reliability engineers. I added my list and hadn’t seen any other links added. There must be more than the few I know about – what can you add to this list? [Read more…]

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International Day of Failure

In light of the International Day of Failure, Oct 13th, let’s consider failure from a reliability engineer’s point of view. We work to understand and avoid product failures. When a product fails to deliver the desired performance attribute, it is tossed away, returned, replaced, repaired, or tolerated. This may occur before or after the product’s value has been achieved. [Read more…]

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Dependability

Dependability

Ran across an interesting graphic in a new book recently. It single-handedly placed dependability in its proper context. It is an umbrella term that includes most of what we commonly think of as reliability and the other ‘ilities.’ It encompasses the various connotations of dependable and reliable that are conveyed during common use. And, the term dependability permits the overarching context for defining very clearly the various [Read more…]

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Root Cause Knowledge and Models

Root Cause Knowledge and Models

Two short questions to evaluate your knowledge of failure mechanisms (root causes) and common reliability models. The answers will be posted in a comment, later.

Which of the following failure root causes is most likely NOT due to power line variation (electronic-based product)?

A. Circuit design margin exceeded
B. Power dissipation
C. In-rush current response
D. Mechanical fatigue [Read more…]

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Two Pumps Problem

Two Pumps Problem

Let’s say we have two identical pumps share a load in parallel. The failure rate for a pump in this mode of operation is 0.0002 failures per hour. If one pump has to carry the full load alone, that pumps failure rate increases to 0.0009 failures per hour.

What is the reliability of the two pump system over a 168 hour week of operation? [Read more…]

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AQL decision

Recently I received a question related to setting an Acceptable Quality Level (AQL) for a sampling of fielded electricity meters. The question was on how to select the right AQL for use with the sampling plan. I was not sure from the question if the sample would determine if the population would be replaced or not (expensive), or simply an experiement to determine how the meters are doing after 15 years of service (information only). [Read more…]