Your Reliability Engineering Professional Development Site
A listing in reverse chronological order of articles by:
While the construction of control charts is relatively straight-forward, often a more difficult question is “how do I know what process characteristic to control in the first place?” Clearly, controlling “everything” is not feasible or a smart use of limited resources. [Read more…]
I learned actuarial methods working for the USAF Logistics Command. We used actuarial rates to forecast demands and recommend stock levels for expensive engines tracked by serial number, hours, and cycles. I had a hunch that actuarial methods could be applied to all service parts, without life data. [Read more…]
In this article post, we formally define or describe the basic terminology that is commonly used in Design of Experiments. Some of the terms we have already been using in prior posts, but they will also be presented here for completeness. This is Part I of a two part article covering DOE Terminology. [Read more…]
Ergodicity means that cross-section probabilities equal longitudinal lifetime probabilities. (“Ergos” is Greek for “work.” Think of “ergonomics”.) Ergodicity means that we can estimate age-specific field reliability functions from cross-section data: ships (installed base) and returns (complaints, failures, service parts’ sales, etc.). Ships and returns provide information about lifetimes. Returns are the superpositions of failures of products or their parts started at different times. What does ergodicity have to do with toilet paper? [Read more…]
“If no one ever took risks, Michelangelo would have painted the Sistine floor.” – Neil Simon
FMEA and Risk Management are two distinct bodies of knowledge. This article explores some of the interactions between these two important methods. It is not intended to be a complete analysis of the similarities, differences, and linkages between FMEA and risk management. Rather, it is a high-level overview.
Imagine you were a rancher with a herd of cattle and a small field in which to graze them. One of your primary concerns include determining how many cattle the field could support. With too few cattle, you give up potential earnings that the field could readily sustain. But too many cattle consume the grass faster than the field could replenish it, resulting in malnourished cattle and degraded land quality.
Therefore, as a rancher with long-term prospects, inspecting and maintaining the field, planting new grass, and limiting the number of new cattle in the field all become a cornerstone of your business model. [Read more…]
Statistically based DOE provides several advantages over more simplistic approaches such “one-factor-at-a-time” experimentation. These advantages include:
Andrew Vázsonyi led an interesting life. He collaborated with mathematician Paul Erdös, he was co-founder of The Institute of Management Sciences, and he wrote “Which Door has the Cadillac: Adventures of a Real-Life Mathematician”. Around 1970, Andrew Vázsonyi interviewed for a teaching job in Sauder School of Business, University of British Columbia. During the job interview, he taught us Gozinto Theory. [Read more…]
Proper control chart selection is critical to realizing the benefits of Statistical Process Control. Many factors should be considered when choosing a control chart for a given application. These include:
This strange word andragogy was popularized in the early 1970’s by educational researcher, Malcolm Knowles. It is etymologically rooted in the Greek language from two words “aner”, which means “man” and “agogos”, which means “to lead”. Fused together, andragogy means “leading men”, or to paraphrase, leading or educating adults. Andragogy is often contrasted with pedagogy, typically referring to the education of children. [Read more…]
Thems that die’ll be the lucky ones.
~ Robert Louis Stevenson
This post is a continuation of the series “Is the HALT a Life Test or not?”
Test two samples and demonstrate reliability R=0,99 over a lifetime with CL=0,99. This is real. But what payment will we pay, besides the duration of the test on triple lifetime, which can be significantly accelerated by the way? [Read more…]
Statistically based DOE provides several advantages over more simplistic approaches such “one-factor-at-a-time” experimentation. These advantages include:
This article will explore the first two advantages in a bit more detail. The second two advantages will be discussed in the next article post. [Read more…]
Myron Tribus’ UCLA Statistical Thermodynamics class introduced me to entropy, -SUM[p(t)ln(p(t))]. (p(t) is the probability of state t of a system.) Professor Tribus later advocated maximum-entropy reliability estimation, because that “…best represents the current state of knowledge about a system…” [Principle of maximum entropy – Wikipedia] Caution! This article contains statistical neurohazards.
Claude Shannon wrote that entropy (log base 2) represents information bits, “…an absolute mathematical limit on how well data from the source can be losslessly compressed onto a perfectly noiseless channel.” [Beirlant et al.]
Maximum likelihood estimation is one way to estimate reliability from data. It maximizes the probability density function of observed data, PRODUCT[p(t)], e.g., for observed failures at ages t. It is equivalent to maximize -SUM[ln(p(t)]. Maximum entropy reliability estimation maximizes entropy -SUM[p(t)ln(p(t)]. That’s same as maximizing the expected value, -SUM[p(t)ln(p(t)], of the log likelihood -ln(p(t). Fine, if you have life data, ages at failures t censored or not. [Read more…]
Statistical Process Control charts have been called the Voice of the Process. Progressive manufacturers utilize control charts to “listen” to their processes so that potentially harmful changes will be quickly detected and rectified. However, not all SPC programs deliver to their highest capability as there are many elements to get right to achieve maximum utility. Highly effective SPC programs combine technical competencies, such as using an appropriate chart and sample size for the application, with effective management techniques such as enabling operator buy-in and involvement. This article identifies ten keys that unleash the power of SPC. [Read more…]
Ralph Evans was editor of the IEEE Transactions on Reliability from 1969 until 2004. He was a very good editor for my 1977 article, and he used me as a reviewer, because I was critical of BS and academic exercises. Ralph moved to University Retirement Community, Davis, CA. He died in 2013, https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6587564. I wish I’d known he lived nearby so I could have visited and argued with him.
Ralph’s editorials [1 and 2] pled, “Data, Data, Oh Where Art Thou Data?” He wrote, “Field-data are largely garbage. I believe they deserve all the negative thinking possible.” “True field-data are wonderful-much better than fancy equations. Unfortunately, they are very difficult to get. Thus data from the field are largely garbage because they do not represent what really happened.” [Read more…]
