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

Issue 4, June 2001

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

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Hot Topics  

Analyzing Step-Stress Data
Step-stress testing is a popular method of conducting accelerated tests. In a step-stress test, the units are tested at a given stress level for a fixed amount of time. At the end of that time, if there are units surviving, the stress level is increased and held for another amount of time. This process is repeated until all of the test units are failed or the predetermined test time has expired. This method of accelerated testing is a good way to obtain failures in a relatively short amount of time. However, analyzing step-stress data has been rather difficult and practitioners have generally had to rely on shortcuts or estimations to obtain reliability information from step-stress data. Now, ReliaSoft offers a tool that can allow the user to conduct a complete analysis of step-stress data, instead of having to resort to questionable shortcuts or assumption-laden estimations. This article gives a case study of a step-stress test and the use of ReliaSoft's ALTA 6 PRO to analyze the data from the test. The cumulative damage model is used to obtain an analytical solution for data with time-varying stress.

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Reliability Basics  

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

What Are Confidence Bounds?
One of the most confusing concepts to a novice reliability engineer is estimating the precision of an estimate. This is an important concept in the field of reliability engineering, leading to the use of confidence intervals. This subject can be confusing, as confidence is "the probability of a probability." However, the use of confidence in reliability is becoming more common as more organizations include confidence bounds in their reliability requirements. In this article, we will briefly present the concept, in relatively simple terms, and based on common sense.

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Tool Tips  

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

  • What do the parameters B and C represent in ALTA?

  • How can I quickly insert identical units in series in a BlockSim reliability block diagram?

  • How can I show information from more than one data set in one plot in Weibull++?

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Hot News

* Pre-Release Offer for the ALTA 6 and ALTA 6 PRO Software, Save up to $1000 - ReliaSoft's ALTA 6 and ALTA 6 PRO software are scheduled for release in July 2001. ReliaSoft's first version of ALTA enabled engineers to get estimates for the population cdf, confidence intervals and other quantities of interest at use level from data obtained through an accelerated test where the stresses applied to the units were not a function of time. ALTA 6 PRO expands this functionality, allowing the user to incorporate more models and more stress types in their analyses. Finally, the reliability engineer has the tools to analyze accelerated life data obtained with stresses that vary over time. Take advantage of the pre-release offer to save 20% off of the standard price. For more information, see

*Next Seminar in San Diego, August 20-24 - The next ReliaSoft "Master the Subject, Master the Tools" seminar will be held in San Diego, California from August 20-24, 2001 at the Holiday Inn on the Bay. 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 registration, see


*ReliaSoft's BlockSim and RAC's PRISM tool integration - The latest service release of BlockSim includes the integration of the Reliability Analysis Center's (RAC) PRISM® software, thus allowing access to RAC's extensive electronic failure rate database (included in PRISM) as an integrated add-on to the BlockSim application. To use this functionality, you must have both PRISM and BlockSim installed on your computer. Both products are available as a package from ReliaSoft.

From The Edge  

Each quarter, ReliaSoft publishes Reliability Edge, a printed journal that includes articles and information related to the field of reliability engineering. The next issue of Reliability Edge will be distributed in July 2001. This edition will include articles on test design and analysis, accelerated life data analysis models, degradation analysis, an introduction to the new ALTA 6 and ALTA 6 PRO software and other articles of interest.

Our readers are encouraged to provide feedback on the articles included in Reliability Edge and to suggest topics to be included in future issues. If you have a letter or article that you would like to submit for publication, please contact our editorial staff.

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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