Articles

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

Reliability Maturity Matrix

The concept of a maturity model is not new. It provides a means to identify the current state and illuminate the possible improvements to a reliability program. The matrix serves a guide to assist an organization in improving its program.

The matrix has five stages. In general, the higher stages are most cost effective and efficient at achieving higher rates of product reliability performance. These stages—uncertainty, awaking, enlightenment, wisdom, and certainty—are described in today’s post. [Read more…]

by Fred Schenkelberg 2 Comments

Hypothesis Test Selection

Over the past few weeks, we have explored about 8 different hypothesis test formulas. There are more. So, how do you determine which test to perform? Well, that depends on the question you are trying to answer and the type of data you’re dealing with. [Read more…]

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Decision Focus

An essential element of a successful reliability program is the notion that all reliability activity relates to decisions. If you are performing a HALT because it is listed in the product development guidelines, or because it was carried over from the last program’s plan, and the HALT results are not part of the design improvement decision-making process, then you probably should not be doing so. If the HALT results yield little or no information (e.g., it is just being checked off the list as accomplished) then the HALT itself provides little or no value. [Read more…]

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The Paired-Comparison Hypotheses Test for Variances

The F-test provides a means to compare paired data variances. It is a variance hypothesis test.

If we are exploring the precision of one measuring device or another, or we are comparing assembly processes, we often want to know if the variance is different or not.
Working with data from normal distributions from two different processes or devices, we know from statistical theory that the ratio (s1)2 / (s2)2 is described by the F distribution.
There are three hypothesis test possible, basically to test if the population variances are different, or one is less than or greater than the other. The following details the three test’s null and alternative hypotheses. [Read more…]

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Product Reliability Participants part 7

This will be the last of the series, considering the different positions in an organization that deals with product reliability. We’ve moved away from the positions where the focus on reliability is central, but there are important considerations in relation to product reliability for each of these roles still. In this concluding post the subjects are the manufacturing team, and field service and call center staffs. [Read more…]

by Fred Schenkelberg 3 Comments

CRE Calculator

A key preparation step for the CRE exam is to have and know how to use a simple calculator. I use my smartphone and a calculator app – and I would not be permitted to use the phone during the exam. Same with tablets, computers, and other common tools that we now take for granted. [Read more…]

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Product Reliability Participants part 6

In this installment of the series dealing with the myriad participants within an organization, we’ll start with failure analysis specialists, before moving to marketing and sales, and finally getting to the finance team. We’re moving away from the positions where the focus on reliability is central, but there are important considerations in relation to product reliability for each of these roles still. The next post in this series will be the final one. [Read more…]

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Chebyshev’s Inequality

As with the Markov Inequality, we may find useful information from a list of values, say time to failure data. Again, none of the numbers may be negative for this to apply, yet with life data that is rarely the case.

Short on time- a common situation for reliability engineers; we have only the mean, standard deviation and number of values in a list. And, we need to say something about the data and the number or fraction of value above a specific value. [Read more…]

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Markov Inequalities

If we have a list of numbers, saw cycles to failure for a test. None are negative. And, we do not have time for a complete analysis before being asked about the results.

What can we do?

In this case, the Markov Inequality may prove useful for a quick assessment of the results. [Read more…]

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Product Reliability Participants part 5

Continuing the series where we examine various roles within an organization and the ways in which each role interacts and affects product reliability, this post will start off with procurement engineers and managers. Since each role hereafter is a bit less involved, multiple roles will be grouped together. After procurement, we’ll take a look at warranty managers. [Read more…]

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Product Reliability Participants part 4

The last post moved into the role of quality and reliability engineers, and the influence that leadership in design and product development has on the product reliability process. Similarly, this post will move to Q & R managers, again looking at the role of that position in relation to product reliability.

[Read more…]

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Product Reliability Participants part 3

The last post in this series dealt with management in design and the influence that leadership in design and product development has on the product reliability process. This post will turn to quality and reliability (Q & R) engineers, again looking at the role of that position in relation to product reliability. The next post in this series will take a look at the role of quality and reliability managers. [Read more…]

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Hypothesis Tests for Variance Case II

The chi-square (Χ²) test provides the basis for the second case of hypothesis tests for variances. In this case, we want to compare observed and expected frequencies, or counts, of outcomes when there is no defined variance. In other words, we are working with attribute data. [Read more…]

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Product Reliability Participants – Part 2

The last post in this series dealt with the design team, and the influence that team has on the product reliability process. This post will turn to product development and design managers, again looking at the role of that position in relation to product reliability. The series of posts on reliability participants will continue after today’s post with the roles of quality and reliability engineers and managers.

[Read more…]

by Fred Schenkelberg 2 Comments

Hypothesis Un-Equal Variance

Hypothesis testing of data may include two populations that have un-equal standard deviations. The t-test for differences considered in a previous post used the assumption of equal variances to pool the variance value. In this test, we want to consider if one population is different in some way than the other and we use the samples from each population directly even if the population have difference variances. [Read more…]