Articles

Find all articles across all article series listed in reverse chronological order.

Sample Size Success Testing

One of the most often asked questions of reliability professionals (or statisticians) is related to how many samples for a test? This typically is not an easy question to resolve without some work and knowledge of the testing in question. We are often asked anyway, and expected to have an answer.

While not the most often asked question on the CRE exam, you might see something related. Budget planning, prototype counts, test equipment sizing, etc. all need an estimate for sample size. [Read more…]

by Fred Schenkelberg 3 Comments

Reliability Apportionment

Diverging from reliability statistics for a post or two, let’s consider one way which R(t), reliability at time, t, is useful during the design phase of a product. Apportionment is the breakdown or allocation of reliability goals or objectives to elements within the product.

Overall, the product’s reliability is just one number, and it represents what the customer will experience with the product. During design, we often work on subsystems and components. Having a meaningful way to describe the reliability requirements that also assists the team to meet the overall product goal, is, well, useful. [Read more…]

by Fred Schenkelberg 5 Comments

Statistical Terms about Variation

“Statistics is the language of variation.” I’m sure that is a quote by someone, not me, though. It is true. Statistics is all about variation. In this post let’s explore some of the ways statisticians talk about data and specifically the amount of dispersion in the data. [Read more…]

by Fred Schenkelberg 1 Comment

Statistical Terms

This is hopefully completely a review. The mastery of basic statistical terms is important as many of the questions on the CRE are statistical in nature and rely on your understanding the terms. Let’s simply review the terms, and do let me know if you have any questions.

Let’s take a random sample from a population. Given a [Read more…]

by Fred Schenkelberg 1 Comment

Role of Reliability Statistics

Generally, I do not talk about statistics before 10am – it’s not polite.

As a reliability professional, statistics is a central feature of the value I bring to the team. And, not just the reliability statistics, all stats. It continues to amaze me how many engineers, scientists, and professionals tend to avoid statistics. [Read more…]

by Fred Schenkelberg 5 Comments

The Four Functions

There are four functions related to life distributions of importance to reliability engineering.

Nearly all textbooks on reliability either introduce or use these functions. Likewise, nearly every calculation related to reliability statistics also uses at least one of functions.

Suppose we produced 100 units of a product and tracked them all till failure over time.

Eventually, all of them would fail. And, unlike the Parson’s One Hoss Shay the products and their components would not all fail at the same time.

One way to track the failures over time is to use a simple histogram.

By plotting the number of failures each month, for example, we would [Read more…]

by Fred Schenkelberg 1 Comment

Basic Statistics

Understanding the math is critical not only for the exam, but it is also important for your ability to function as a reliability professional.

Most of us did not enjoy our undergraduate statistics course. It was just another course to endure as part of being in an engineering or science track.

The basic concepts and approaches to working with data are fundamental for some many situations. [Read more…]

by Fred Schenkelberg Leave a Comment

Engineering Management

As 12%* of the CRE exam, this is a major section, yet not a very difficult one. There are three basic areas:

strategic management
reliability program management
ethics, safety, and reliability

If you’ve ever needed to secure funding or samples for a reliability test or had to respond to customer field returns, then you probably already understand the value of reliability.

In some businesses, product reliability is critical to the product’s success. Some businesses strive to be the leading ‘reliable’ producer in the market. [Read more…]

by Fred Schenkelberg Leave a Comment

Getting Started Preparing for the CRE Exam

I’ve learned a lot in my career and have attempted to help others to the best of my ability.

Teaching is fun.

It is also enjoyable to know a little of what I’ve learned from others may continue to be passed along.

The ASQ CRE certification is a milestone in a reliability engineer’s career. It is not an end nor a beginning, just a milestone to mark the achievement.

The CRE BOK encompasses a broad range of concepts and tools.

Passing the exam marks the person as having mastered the body of knowledge as laid out in the ASQ CRE BOK.