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CRE Preparation Notes

Prep notes for ASQ Certified Reliability Engineer exam ISSN 2165-8633

The CRE Preparation Notes series provides you with short practical tutorials on all the elements that make up the ASQ CRE body of knowledge. The articles provide introductory material, basics, how-tos, examples, and practical use guidance for the full range of reliability engineering concepts, terms, tools, and practices.

Keep your knowledge fresh by regularly reviewing topics and tools that make up reliability engineering.

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You will find the most recent tutorials in reverse chronological order below.

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Two Proportions Hypothesis Testing

Two Proportions Hypothesis Testing

In the article, Hypothesis Tests for Proportion, the comparison is between a given value and the sample. In this case, let’s compare two populations. We take a sample which provides a proportion representing each population and determines if the populations are different from each other based on the two samples.

The exact solution uses the Binomial distribution, yet when np and 1 – np are greater than 5, then we can use a normal approximation for the test statistic and critical value. [Read more…]

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Solving a Reliability Optimization Example

Solving a Reliability Optimization Example

In the previous article, What is Reliability Optimization, we defined the concept. One of the elements of optimization is identifying which elements of a system to focus improvement efforts on.

Simply improving every element of a design may provide an overall improvement of reliability performance.

Given constraints such as time or funding, selecting the specific few elements that would provide the most improvement is key. [Read more…]

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What is Reliability Optimization?

What is Reliability Optimization?

Delivering the best reliability performance within the various constraints imposed.

Without constraints such as budget, time to market, customer expectation, product functional capabilities, and product weight, you certainly could design and deliver a highly reliable product.

There always are constraints.

In the Oliver Wendall Holmes poem, The One Hoss Shay, the deacon procures the strongest oak, the supplest leather, and the best of best materials. Cost was not a constraint. And the shay lasted 100 years to the day.

If the technology permits there may be stronger or more durable components available for a price, yet cost is often a limiting factor. [Read more…]

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Deciding What Should Have Fault Tolerance

Deciding What Should Have Fault Tolerance

In some circumstances, it is desirable to ensure the system continues to operate even if there is an internal failure. An aircraft navigation system should be able to operate even if an internal dc-dc regulator fails, for example.

Not everything within some systems benefits by being fault tolerant.

For example, a failure of a cabin reading light over a passenger seat is not critical to the safe operation of the aircraft, thus is likely not created to be fault tolerant. One criterion to determine what should be fault tolerant is the criticality of the function the system provides.

This also applies to specific subsystems within a system allowing some elements to be created fault tolerant and others within the system not. [Read more…]

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Fault Tolerance Basics

Fault Tolerance Basics

Fault tolerance is a system that is reliant to the failure of elements within the system. It also may be called a fail safe design.

A fault tolerant system may continue to operate just fine, after one of the power supplies fails, for example. Or it may operate in a reduced or degraded state.

Other systems may have a ‘limp home’ condition, allowing the system to save critical data or allowing you to drive to a safe place to change a flat tire. [Read more…]

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Reliability as Part of Every Decision

Reliability as Part of Every Decision

Concurrent engineering is a common approach that pairs the development of the product design and it’s supporting manufacturing processes through the development process.

Design engineers may require the creation of new manufacturing processes to achieve specific material properties, component performance, or mechanical, electrical or software tolerances. [Read more…]

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Reliability in Product and Process Development

Reliability in Product and Process Development

A product or system’s actual reliability performance is a function of the design, assembly, and use.

Decisions made during design predominately create the inherent reliability capability performance.

The selected components, manufacturing, transportation and installation all can add variability and errors to the product, often reducing the actual reliability performance.

The use conditions and maintenance add another layer of variability, again reducing reliability capability. [Read more…]

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Software Defect Phase Containment

Software Defect Phase Containment

Software Defect Phase Containment

The software element of products continues to grow.

Likewise, the number of field failures due to software issues continues to grow. Writing code is relatively straight forward, and some may even say it’s fun.

The process of debugging, or finding and fixing software defects, is not fun. [Read more…]

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Approaches to Assess Customer Reliability Needs

Approaches to Assess Customer Reliability Needs

Approaches to Assess Customer Reliability Needs

Just asking a customer how reliable they want your product often provokes an honest answer. The customer, and you most likely, do not want any failures.

Failures are troublesome or in some cases dangerous.

You and your customers realize that not every unit produced will operate over a long and useful life. There is some chance that something will fail. The definition of ‘some’ is often vague. [Read more…]

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Reliability Role in Safety and Liability

Reliability Role in Safety and Liability

Reliability Role in Safety and Liability

The reliability engineer may have many roles within an organization.

You may be specialized and focused only on the analysis of field data. Or you may be a member of the organization’s strategic leadership team.

You might support one or more product development teams, or work with a team of reliability professionals supporting just one subsystem. [Read more…]

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Ethics and Your Work as a Reliability Engineer

Ethics and Your Work as a Reliability Engineer

Ethics relate to the moral correctness of a person’s behavior given the groups moral principles.

Society, in general, has a set of standard expectations to guide our behavior. This includes fundamentals such as not harming others or behaving in a deceitful manner.

Religious, professional and informal ‘codes’ document the set or principles which guide our behavior in line with moral correctness. [Read more…]

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2 Versions of Product Life Cycle Phases

2 Versions of Product Life Cycle Phases

Each organization creates their own version of a product life cycle.

Often there are phase gate reviews that signal a transition from one phase to the next. In general, each set of phases follows a common progression from idea to retirement.

There are many references that include a description of the life cycle phases, so let’s explore two of them. [Read more…]