Reliability HotWire: eMagazine for the Reliability Professional
Reliability HotWire

Issue 3, May 2001

Tool Tips
How do I obtain component failure and repair information for RBD blocks in BlockSim?
The recommended way to obtain failure and repair information is through empirical testing. This may be through in-house testing of components and parts or from information supplied by the vendor. ReliaSoft takes the position that this type of directly-obtained component information is the best way to represent the failure and repair characteristics of the components, and consequently will produce the best results for the system-level analysis. However, ReliaSoft recognizes that this information may not always be available for those who wish to perform a system reliability analysis. This may be due to a lack of affordable parts for testing early in the development process or simply due to the desire to "blue sky" and play around with potential design configurations without having to undergo costly testing procedures. Consequently, BlockSim can also import generic failure rates from the PRISM database developed by the Reliability Analysis Center (RAC). PRISM is a new RAC software tool with the next generation of electronic component failure rate models and a comprehensive searchable database of observed field failure rates modeled after RAC's successful NPRD and EPRD data book series. The PRISM concept accounts for the myriad of factors that can influence system reliability, combining all those factors into an integrated system reliability assessment resource. For more information about BlockSim's integration with PRISM, see

How can I change the default plot settings for multi-plots in Weibull++?
The defaults for multi-plot settings in Weibull++ can be changed as easily as the settings for a single plot. In the Plot Setup window, click the Multi-Setup button. The Multiple Plot Setup window will appear.

Weibull++ Multiple Plot Setup Window

Make the desired adjustments to the settings for each of the desired Multiple Sets, then click OK. The Multiple Plot Setup window will close and return to the Plot Setup window.

Weibull++ Plot Setup Window

Click the Set Default button to accept the multiple plot settings as the default setting. (NOTE: The values of the multi-plot can be reset to those of the current single plot settings by right-clicking the Set Default button. This can be handy for making wholesale changes to the default multiple plot settings without having to manually the settings for each multiple set.) 

I have a data set with two stresses in ALTA. How can I insure that both stresses will be taken into account in the analysis and plotting? 
When considering a data set with more than one stress in ALTA, you must make certain that you are using a life-stress relationship that can support multiple stresses, such as the temperature-humidity model or the temperature-nonthermal model. If another life-stress relationship is selected (i.e., Arrhenius, Eyring, or inverse power law), the data will be analyzed as if there were only one stress acting as an acceleration factor. Consequently, ALTA will only display the analyzed stress factor on the Life vs. Stress, STD vs. Stress, or AF vs. Stress plots.


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