Your Reliability Engineering Professional Development Site
When using a sample to calculate a statistic we are estimating a population parameter. It is just an estimate and the sample due to the nature of drawing a sample may not create a value (statistic) that is close to the actual value (parameter). [Read more…]
By Fred Schenkelberg in Reliability Engineering Management
130 pages, published 5/25/2015
It may be possible to pass the CRE exam knowing one formula.
The math elements of the exam may take a bit of time to solve, and knowing reliability statistics well is a good plan heading into the exam. Knowing the exponential distribution reliability function is one that you should memorize. [Read more…]
A reliability block diagram is a graphical and mathematical model of the elements of a system permitting the calculation of system reliability given the reliability of the elements.
The model reflects the reliability performance structure including series, parallel, standby and other arrangements of system elements.
Each block in an RBD represents a component or subsystem of the system. The organization and connecting lines represent the reliability structure of the system and may or may not be representative of the system’s functional block diagram. [Read more…]
Coupled with probability is the duration over which the probability applies.
For example, if we desire 99 of 100 to survive, we must state over which period of time this applies. It is proper to state the couplet of 99% reliable over 1 year.
It is not sufficient to define reliability as ‘5-year product’ as it does not contain the information related to how many are expected to survive the 5 years. Likewise, it is not sufficient to say a product has 5 – 9’s reliability (meaning the probability of failure is less than 0.00001) as it does not contain the duration.
If the product has high reliability for only a few seconds, that does not help us make judgments about the first year of life. [Read more…]
Let’s take a graphical view of reliability improvement that occurs during product development or improvement projects.
If we are making improvements the system reliability should increase. We can use the build, test, fix approach to measure improvements, find failures, design improvements, and repeat. [Read more…]
I’ve recently received a couple of notes from individuals looking at starting a career in reliability engineering. One is a student looking at a career path, another a working engineer with an interesting in reliability.
Both asked how to land a position given no reliability engineering experience.
Hum, I don’t know anyone that had reliability engineering experience before they got started working in reliability engineering. Not counting taking apart the family toaster and trying to repair it before Mom got home as a kid.
Reliability testing and data collection is a messy business.
We rarely receive perfect data where all units involved have a precise time to failure record. Sometimes we do not the precise time to failure information or some of the units are still operating.
The data is censored.
There are a few common types of censoring, each of which has statistical techniques to appropriately account for the unknown elements. [Read more…]
A common expectation consumers have concerning products is that the product works. The product provides value by performing one or more functions. Also, implicit with this expectation is the product will function over some duration. A reliable product meets or exceeds this common expectation.
Every product has a finite duration of successful operation before failure occurs.
A test to determine if the homogeneous Poisson model (HPP) is applicable given the data from an individual system is subject to the non-homogeneous Poisson model (NHPP).
This is an alternative test to using the Kendall-Mann Reverse Arrangement Test. [Read more…]
One approach for reliability improvement is to find the weaknesses or faults, then fix them.
This is best done before shipping to the customer.
You may hear this called the Test, Analyze, and Fix Method (TAAF). Or, you may have heard of it called a Reliability Growth Test program (RGT). Either way, the essence is evaluating prototypes to find specific faults. [Read more…]
Maria Popova recently wrote about the work of James T. Mangan and his book You Can Do Anything!
, published in 1936. In particular she focused on one section titled 14 Ways to Acquire Knowledge
The article is about learning anything, which had me thinking about how to learn reliability engineering. So, without apology let’s explore 14 ways to learn about reliability engineering. [Read more…]
Over the past week or two, I’ve received requests and comments that have given me pause. Why is it that I have time to answer questions and share information? Why do I spend the time to do so in the first place?
I have found that responding to questions or requests for assistance is rewarding.
Today I received a request for help in a job search. Last week it was an employer looking for a perfect candidate. I’ve received questions about graduate school in the US from a Chinese undergraduate. A question on accelerated life testing approaches. Another on maintenance practices and data analysis.
For each, I try to provide an answer or direct to find an answer.
When a product or asset works as it’s expected for as long or longer than expected, we often consider it reliable.
Consumers around the world look for reliable products and services. Some will pay a premium with the desire to obtain failure free value from the purchase. When designing a product or service we often want to create the most reliable item within the constraints of time, resources, and cost. Designers and engineers may add margin or safety factors into calculations and decisions to avoid failures.
Many of us have heard that fixing a design is orders of magnitude less expensive early the product lifecycle. Product recalled or major failures can damage profits and brand image.
Here are three ways you can invest in improving product reliability. [Read more…]
When this posts I should be home from Nepal and mostly recovered. So, back to more details going forward. Take a look, work the problem, solve it, then show your work. Comment with why you chose your response and why you didn’t select one of the others. [Read more…]
