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The Liability Part of Reliability Engineering

The Liability Part of Reliability Engineering

In many parts of the world ‘caveat emptor’ [let the buyer beware] no longer applies.

The producer and distributors of products are liable for their products.

This extends beyond product failures and a warranty claim. Today the company is liable for to make right any loss or damage incurred by the use of the product.

Courts and laws around the world reflect the protection of users of products from adverse consequences due to a negligent design and assembly practices.

The producer of a product must consider the user’s safety and provide reasonable safeguards.

This applies even when the user misuses or abuses a product. [Read more…]

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Basic Approach to Achieve Process Stability

Basic Approach to Achieve Process Stability

Everything varies.

Your vendors provide components with a range of values. Your production process varies, too.

Creating, monitoring, and maintaining process stability enhances your product reliability performance.

When I started my professional life as a manufacturing engineer, a senior engineer told me we take a product design and can only make it worse.

He said if we could make every unit exactly according to the nominal values of the drawing, every unit would work well. [Read more…]

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Use a Delta Program to Minimize Early Field Failures

Use a Delta Program to Minimize Early Field Failures

Failures happen. Sometimes product failures happen quickly.

You just bought a new feature rich computer and discover it doesn’t work. Right out of the box, it will not power up. Conversations with the tech support and it’s a trip back to the store.

The failures that occur early the in the life of a product tend —

this ‘tend’ really is just a vague ‘in general’

…tend to occur because of manufacturing errors or shipping/installation damage.

Not always, though. [Read more…]

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Standby Redundancy, Equal Failure Rates, Imperfect Switching

Standby Redundancy, Equal Failure Rates, Imperfect Switching

First off, switches are not perfect, so this situation includes the reliability of the switch. Switch reliability may be a factor of storage time, probability of actually working when called on to work, or number of switching cycles. Each switch technology may be slightly different. For this equation, you need the reliability or probability of success given the primary unit has failed. Although we are assume the switch reliability is independent of the primary unit reliability and subsequent failure.
[Read more…]

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Tolerance Intervals for Normal Distribution Based Set of Data

Tolerance Intervals for Normal Distribution Based Set of Data

This is not the same as a confidence interval. For a mean or standard deviation, we can calculate the likelihood that the true parameter is within a range of values — confidence interval concerning a parameter.

A tolerance interval applies to the individual readings, not the statistics. The interval contains a certain proportion of the values within the distribution of individual data points. The endpoints are tolerance limits. [Read more…]

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Reliability Benefits of Alpha and Beta Testing

Reliability Benefits of Alpha and Beta Testing

Your customers are your best testers for your next product. They will explore the features. Expose the product to use conditions in unconscious ways. And, they will let you what they consider failures without needing the specification document.

During the development process, you and team may work to understand what customer may want or expect for the new product. You may even conduct focus groups or review past product field failures and call center records. [Read more…]

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Mechanical Systems Reliability Testing

Mechanical Systems Reliability Testing

Mechanical systems wear out and fail eventually. The ability of a structure to support a load, move through the specified range of motion, or spin degrades with use and time. Even our joints eventually wear out.

Accelerated life testing (ALT) has plenty of literature concerning the failure mechanisms unique to electronic components and materials. This is partially due to the limited number of unique electronic components compared to the often custom mechanical designs. ALT also has value as it provides information about a system’s reliability performance in the future.

Let’s explore an example of mechanical reliability testing (an ALT)  in order to outline a basic approach to ALT design and analysis. [Read more…]

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Interpolation within Distribution Tables

Interpolation within Distribution Tables

EDITED BY JOHN HEALY

Most statistics books and the CRE Primer have tables that permit you to avoid calculating the probability for common distributions. The normal distribution requires numerical methods to conduct the calculations and would not be feasible during the CRE exam. [Read more…]

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Life Estimates Based on Supplier Data

Life Estimates Based on Supplier Data

Suppliers often include reliability information along with performance specifications.

We look for reliability statements as one part of the selection process to ascertain if the component is likely to have sufficient reliability.

When the vendor’s data is clearly stated and meaningful, that information saves us from potentially having to conduct our own reliability evaluations. [Read more…]