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

Issue 19, September 2002

*Hot Topics
*Reliability Basics
*Tool Tips
*Hot News
*Contribute to HotWire

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Hot Topics  
Looking at Thermal Cycling Data in Quantitative Accelerated Life Testing 
In the growing field of accelerated testing, the ability to analyze data with a time-varying stress (e.g. step-stress) is becoming more and more popular. Analysis of such data used to be very difficult, if not impossible at times, but ReliaSoft's ALTA PRO software can analyze data from an accelerated life test where the applied stress is time-varying. The time-dependent stress can be any continuous function, such as a step-stress or ramp stress. Thermal cycling is another type of time-varying stress profile. At first glance, it would seem that to conduct the analysis for data from this type of test you would obviously treat the thermal cycling as a time-varying stress in ALTA PRO. This seems logical, after all it is a time-varying stress, so why not treat it as such? To answer that question, we have to look at the underlying models utilized for time-varying stresses. These models assume that applied stress (or stimulus) has a single effect, i.e. the higher the stress the greater the damage, whereas in the case of thermal cycling the stress may cause damage at both high and low stresses. In other words, blindly entering the stress as an equation describing the thermal cycle would generate erroneous results. To analyze this type of data properly, the stimuli in thermal cycling need to be identified and treated accordingly. One option is to treat a simple thermal cycle as two constant stresses. 

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

Contour Plots and Confidence Bounds on Parameters (Part II)
In last month's issue of the HotWire we took a look at Contour Plots and Confidence Bounds on Parameters and in this month's issue we will continue with this subject. In ReliaSoft's Weibull++ software, there are two locations in which you can view likelihood ratio confidence bounds on the parameters: the Quick Calculation Pad (QCP) and the contour plot. This article describes how to configure Weibull++ to calculate the confidence bounds using the likelihood ratio method, how to generate and use contour plots to compare data sets and how to obtain LR confidence bounds on the parameters from the QCP. This article also examines any differences between the confidence bounds results obtained from contour plots and from the QCP in Weibull++.

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Tool Tips  

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

  • What are the policy guidelines for a single-user license for ReliaSoft software products?

  • How can the reliability equation be toggled on/off when conducting analysis of an RBD in BlockSim?

  • For a system with subdiagram(s) in BlockSim, how can the speed of the analysis be increased?

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Hot News
* Reliability Training Seminars - Upcoming ReliaSoft public reliability training seminars include:


QALT Boot Camp intensive three day course on advanced topics, concepts and applications of quantitative accelerated life testing (QALT) analysis, such as time-varying stress, multiple stress testing and ReliaSoft's ALTA PRO software: November 6 - 8, 2002 in Tucson, Arizona. For more information, see Please remember that registered users of the ALTA PRO software are entitled to attend this seminar at no cost.
- Master the Subject, Master the Tools training seminar for life data analysis, accelerated life data analysis and system reliability analysis: November 18 - 22, 2002 in Tucson, Arizona. For more information, see


New Distributor in Asia - ReliaSoft has recently appointed DACQ Technologies Pte Ltd as a distributor for Singapore, Malaysia, and Thailand. You can contact DACQ Technologies Pte Ltd at:

DACQ Technologies Pte Ltd
Mr. Hong An Lin
Block 1091 Lower Delta Road #03-06
Singapore 169292
Phone: 65-62769077
Fax: 65-62768077

To kick off the new partnership, ReliaSoft has scheduled a Master the Subject, Master the Tools training seminar in Singapore between December 9 - 13, 2002. If you are interested in attending, please contact DACQ Technologies Pte Ltd.

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.

Copyright 2002 ReliaSoft Corporation, ALL RIGHTS RESERVED