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

Issue 45, November 2004

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

Bringing It All Together

The construction or enhancement of a reliability program will, by necessity, be specially adapted according to the specific needs and structure of the organization. As is the case with many other situations, "form follows function," and the form of the reliability program will follow the function of the organization that is implementing it. However, it is necessary to make sure that the information that is generated by the reliability program is fed back throughout the organization so that the maximum benefits of the program can be achieved. Instituting a reliability program merely for the sake of having a reliability program will ultimately be of no benefit to anyone. If the reliability program is not feeding back useful information to all of the areas of the organization that need it, it will eventually atrophy and become just a little-utilized enclave of the larger organization. Of course, it is unlikely that an organization that has gone to the trouble of implementing a high-efficiency reliability program will allow such a program to wither and die, but it is important to make sure that the reliability program's benefits reach all the areas that it can.

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Reliability Basics

Common Shape Parameter Likelihood Ratio Test

In order to assess the assumption of a common shape parameter among the data obtained at various stress levels, the likelihood ratio (LR) test can be utilized. This test applies to any distribution with a shape parameter. In the case of ALTA 6, it applies to the Weibull and lognormal distributions. When either of these is used as the underlying life distribution, the shape parameter is assumed to be constant across different stress levels (i.e. stress independent). This article shows how to assess the validity of this assumption.

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Tool Tips
  • For the Weibull distribution, what is the difference between the characteristic life and the mean life?

  • When considering complex repairable systems, what is the difference between the Weibull distribution and the Power Law model?

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Hot News
* 51st Annual Reliability & Maintainability Symposium (RAMS) - ReliaSoft Corporation will be a Diamond Level Sponsor and a participant at RAMS this winter. The event is scheduled for January 24-27, 2005 at the Hilton Alexandria Mark Center in Alexandria, Virginia. Topics related to Reliability, Maintainability, Quality, Risk Management and Safety will be addressed as engineers are exposed to state-of-the-art methods for achieving their R&M objectives. For more information and an Advanced Program, see
* Prediction Software by ReliaSoft ReliaSoft is happy to announce new developments! The finishing touches are being added to our standards based reliability prediction software, Lambda Predict. This software will include MIL-HDBK-217, Bellcore (Telcordia), RDF 2000 and China 299B for the analysis of electronics and related components plus NSWC-98/LE1 for mechanical components. It will also ship with an extensive collection of pre-defined component libraries. For more information on Lambda Predict, please visit If you are interested in receiving a demo upon software release please let us know at
* International Representation ReliaSoft recognizes that todays engineering community is a global endeavor that requires cross communication between different regions of the world. Therefore, ReliaSoft continues to bridge the international gap by staffing and partnering with local professionals in key locations. To the benefit of non-English speaking countries, our regional offices are staffed with multilingual representatives. Many offices have also begun translating Web sites and various resources. If you have an international colleague who could benefit from the reliability engineering resources offered by ReliaSoft, then we encourage you to seek out the professionals we have made available. Here is the directory for all of ReliaSoft's official regional offices and representatives:
* Public Training Event Calendar
November 2004
  - November 15 - 19: MSMT in Tucson, Arizona
  - November 22 - 26: MSMT in Shenzhen, China

     - Register through RS China

  - November 29 - December 3: MSMT in Singapore

     - Register through RS Asia

December 2004
  - December 6 - 8: QALT Boot Camp in Tucson, Arizona
  - December 6 - 8: Reliability Growth, Repairable System Data Analysis and RGA in Tucson, Arizona
  - December 6 - 10: MSMT in Melbourne, Australia

     - Register through RS Asia

  - December 13 - 17: MSMT in Penang, Malaysia

     - Register through RS Asia

  - December 20 - 22: RS 401 in Shah Alam, Malaysia

     - Register through RS Asia

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:
  • Most complex systems, such as automobiles, communication systems, aircraft, aircraft engine controllers, printers, medical diagnostics systems, helicopters, train locomotives, etc., are repaired and are not replaced when they fail. When these systems are fielded or subjected to a customer use environment, it is often of considerable interest to determine the reliability and other performance characteristics under these conditions. Areas of interest may include assessing the expected number of failures during the warranty period, maintaining a minimum mission reliability, addressing the rate of wear-out, determining when to replace or overhaul a system and minimizing life cycle costs. In general, a distribution, such as the Weibull distribution, cannot be used to address these issues. In order to address the reliability characteristics of complex repairable systems, a process is often used instead of a distribution. The most popular process model is the Power Law model. To view the entire article 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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