In this issue:

Issue 94, December 2008

*Hot Topics
*Reliability Basics
*Tool Tips
*Latest Software Updates
*Hot News
*Contribute to HotWire

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Happy Holidays!

From all of us at ReliaSoft... we wish you a joyous holiday season and a new year of peace and happiness.

Hot Topics

Using DOE++ to Analyze Unbalanced Designs
One of the purposes of using Design of Experiments (DOE) is to evaluate which factors have significant effects and how they affect the response of interest to the experimenters. For example, one might examine how the speed and the type of gasoline affect the mileage of a vehicle and which factor has the greater impact. When DOE is used by reliability engineers, the response of interest is product life; a reliability engineer will use DOE to investigate which stresses influence product life and how much they affect life. In order to obtain an accurate estimation, experiments need to be carefully designed. A general requirement is that the design needs to be "balanced." In this article, we will discuss what an unbalanced design is and how it can be analyzed correctly using ReliaSoft's DOE++ software.

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Reliability Basics

MTTF, MTBF, Mean Time between Replacements and MTBF with Scheduled Replacements
Seasoned reliability engineers know that there is a great deal of discussion and confusion regarding the terms MTTF and MTBF. We certainly hope that the addition of two more terms in the title won't scare readers away! In fact, the purpose of this article is to clear up the confusion by defining these terms and using examples to illustrate their differences, as well as discussing the applications of each term. ReliaSoft's software packages Weibull++, RGA and BlockSim will be used for illustration.

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Tool Tips
  • Can I compare analysis results using different settings in DOE++?
  • What are the Severity Class and Failure Probability ratings scales for in Xfmea/RCM++?

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Latest Software Updates
New service releases are now available for Weibull++ (SR 7.5.6), ALTA (SR 7.5.6) and DOE++ (SR 1.0.3). To determine the compile revision of the application on your computer, select About from the Help menu. More Software Downloads...


Application Date Created Version
Weibull++ 7 11/21/08 7.5.6
ALTA 7 11/21/08 7.5.6
DOE++ 11/21/08 1.0.3
Hot News
* 55th Annual Reliability & Maintainability Symposium (RAMS) - ReliaSoft Corporation will be a participant and presenter at RAMS again this winter. This years presentations will include:

"Improving the 1-Parameter Weibull: A Bayesian Approach"
By Alexander Aron, Dr. Harry Guo and Adam Mettas, ReliaSoft Corporation

"Warranty Prediction for Products with Random Stresses and Usages"
By Dr. Harry Guo, Arai Monteforte and Adam Mettas, ReliaSoft Corporation

"Introduction to R&M Management (Reliability from Design Inception to Product Retirement)"
By Dr. Duane Dietrich, ReliaSoft Corporation

RAMS 2009 will be held at The Worthington, A Renaissance Hotel, in Fort Worth, Texas on January 26-29, 2009. As always, our staff of reliability experts will be on hand to provide you with useful information and to demonstrate the capabilities of ReliaSoft's complete suite of tools, including our Web-based XFRACAS application -- so be sure to stop by our booth! For an advance program and registration information, please visit

* ReliaSoft Funds One Year Scholarship - In continued support of the ReliaSoft Risk, Reliability and Maintainability Research Alliance that was established through the University of Arkansas last year, ReliaSoft is proudly providing one year of financial support to a chosen graduate student at this institution.
* North American ARS Proposal Submissions - We have been very pleased with the large turnout of qualified proposal submissions for next years Applied Reliability Symposium. Now that the official submission date (Dec. 5th) has passed, our committee will work diligently to select the finalists. A special thank you goes out to everyone who participated in this years submission drive. It has been exciting to see so many professionals show interest.
Upcoming Public Training Event Calendar
December 2008
December 15 - 19, 2008: RS 540 Reliability and Maintainability Analysis for Repairable Systems in Chennai, India
January 2009
January 19 - 21, 2009: RS 560 Fundamentals of Design for Reliability in Bangalore, India
February 2009
February 2 - 6, 2009: MSMT Foundations in Frankfurt, Germany
February 18 - 20, 2009: RS 522 Advanced System Reliability / Maintainability Analysis in Turin, Italy
February 23 - 27, 2009: MSMT Foundations in Tucson, Arizona
February 23 - 27, 2009: MSMT Foundations in Penang, Malaysia
March 2009
March 16 - 18, 2009: RS 522 Advanced System Reliability / Maintainability Analysis in Tucson, Arizona
March 16 - 20, 2009: RS 540 Reliability and Maintainability Analysis for Repairable Systems in Jakarta, Indonesia
March 19 - 20, 2009: RS 470 Failure Modes, Effects and Criticality Analysis in Tucson, Arizona
March 25 - 27, 2009: International Applied Reliability Symposium in Barcelona, Spain
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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