Reliability HotWire: eMagazine for the Reliability Professional
In this issue:

Issue 11, January 2002

*Hot Topics
*Reliability Basics
*Tool Tips
*Hot News
*From The Edge
*Contribute to HotWire

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Hot Topics  
Customer Usage Profiling
An important requirement for designing useful reliability tests is to have a good idea of how the product is actually going to be used in the field. The tests should be based on a realistic expectation of the customer usage, rather than estimates or "gut feelings" about the way the customer will use the product. Tests based on mere speculation may result in a product that has not been rigorously tested and consequently may run into operational difficulties due to use stress levels being higher than anticipated. On the other hand, tests that are designed with a strong basis of information on how the product will be used will be more realistic and result in an optimized design that will exhibit fewer failures in the field. In this article, we take a look at using customer usage information for reliability applications.

To read more, see 

Reliability Basics  
The purpose of this section is to offer background and advice to the novice reliability engineer.

Nonparametric Analysis
In the last several issues of Reliability HotWire, we have looked at various ways of performing parameter estimations on life data sets. Nonparametric analysis allows the analyst to characterize life data without assuming an underlying distribution. This can be advantageous because it avoids some of the dangers inherent in an analysis where an inappropriate distribution is assumed. However, the analysis is limited to reliability estimates only for the failure times in the data set, thus making it impossible to make reliability predictions outside the range of data values. While this somewhat limits the usefulness of this method, nonparametric analysis can be used as a benchmark against which other parametric analyses can be compared for accuracy.

To read more, see 

Tool Tips  

The Tool Tips section addresses helpful hints and frequently asked questions about ReliaSoft software products.

  • What is the difference between "upper" and "lower" confidence bounds, and "top" and "bottom" confidence bounds?

  • In Weibull++, what does "PNZ" stand for and how does it work?

To read more, see

Hot News
*    Reliability Training at GM Knowledge Center - We are pleased to announce that once again ReliaSoft will be providing training classes for GM employees at the General Motors Knowledge Center in Warren, Michigan. The courses offered will cover three diverse disciplines of reliability engineering and include life data analysis, accelerated life test data analysis and system reliability, maintainability and availability analysis. For more information contact ReliaSoft at +1.520.886.0410 or visit GM’s corporate intranet. Class size is limited. The 2002 class schedule is as follows:
  • February 4-7, 2002 -- Life Data Analysis & Accelerated Life Testing Analysis
  • May 6-9, 2002 -- Life Data Analysis & System Reliability
  • August 5-8, 2002 -- Life Data Analysis & Accelerated Life Testing Analysis
  • October 14-17, 2002 -- Life Data Analysis & System Reliability
*    Next Seminar in Tucson, February 18 - 22  - The next ReliaSoft "Master the Subject, Master the Tools" seminar will be held in Tucson from February 18-22, 2002 at the Sheraton Hotel and Suites. Topics for this five-day seminar include life data analysis, accelerated life testing and system reliability, maintainability and availability. For more information on course content and how to register, see
*    ReliaSoft at RAMS - ReliaSoft will be participating in the 48th Annual Reliability and Maintainability Symposium (RAMS), to be held January 28-31, 2002 at the Seattle Westin Hotel in Seattle, Washington. ReliaSoft personnel will be presenting papers on FRACAS systems, online quality tracking and accelerated testing. Also, ReliaSoft will have a booth in the vendors area where you can get information and demonstrations of ReliaSoft's products and services. We hope to see you there!
From The Edge  

In addition to the monthly Reliability HotWire, ReliaSoft publishes Reliability Edge, a printed journal that includes articles and information related to the field of reliability engineering. Articles of interest in the current edition:

  • Data, Where Art Thou? - As reliability analysis tools become more capable, the availability of accurate and timely data for analysis becomes the limiting factor in the ability to perform effective reliability analyses. The information required for reliability analysis is often stored in various locations within the organization, in multiple formats that may be difficult for the analyst to integrate. This article discusses ways and means of data management to support timely and accurate reliability analyses. See

  • Limitations of the Exponential Distribution for Reliability Analysis - The exponential distribution models the behavior of units that fail at a constant rate, regardless of the accumulated age. Although the distribution is frequently used due to its relative theoretical and mathematical simplicity, the exponential distribution can lead to wildly inaccurate analyses if improperly applied. In order to avoid such inaccuracies, we need to understand the basic constant failure rate assumption of the exponential distribution and examine whether it is supported in our real world applications. This article presents a discussion of these issues. See
Contribute to Hotwire
Contributions Welcomed
As always, your feedback and contributions are appreciated. ReliaSoft is able to provide the most user-friendly reliability software packages and support because we listen to our customers. This applies to our newsletters and publications as well. We welcome any suggestions or contributions you may have for Reliability HotWire. If you have a topic or article that you think would be useful to the readers of Reliability HotWire, feel free to contact us.
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