Reliability HotWire

Reliability HotWire

Issue 122, April 2011

Tool Tips

*How can I customize and annotate plots from ReliaSoft applications?

ReliaSoft applications have a built-in graphics editing tool called ReliaSoft Draw (RS Draw), which allows you to insert text, draw an object, mark a particular point or paste another picture into your plot in order to customize and enhance the presentation.

You can access RS Draw from any plot sheet in ReliaSoft's software. Choose Plot > Edit Plot with RS Draw or click the icon from the plot sheet control panel.

RS Draw

The utility contains a variety of tools for adding text, drawing and manipulating plot objects. There are two ways you can save your customized plot:

  • Save the plot as a graphic file by choosing File > Save. You can view and manipulate the file without having ReliaSoft software installed on your computer. Graphic files can also be transmitted via e-mail or imported into applications such as Microsoft Word® and PowerPoint®. Note that when you exit RS Draw, your changes will not be saved in the plot sheet of the folio.

  • Save the plot with the folio by choosing either File > Transfer to Folio or File > Apply Changes and Close. The command will depend on which ReliaSoft software you are using. Your customizations will be saved in the plot sheet of the folio when you exit RS Draw. You can also further edit the customizations by returning to RS Draw.

Example of a plot graphic that has been annotated with RS Draw.

*How can I use the Comparison Wizard and the Stress-Strength Wizard tools in Weibull++ and ALTA?

The Comparison Wizard is a tool you can use to determine the statistical difference between two populations. Specifically, it calculates the probability that the times-to-failure of one population will be better or worse than the times-to-failure of the second. This allows you to compare life distributions from two alternate designs, manufacturers, lots, assembly lines, etc. in order determine whether the units in the first group will outlast the units in the second.

The function of the Stress-Strength Wizard is similar to the Comparison Wizard, except that it compares a data set containing strength data against a data set containing stress data. This allows you to calculate the probability of failure (i.e., the probability that the stress exceeds the strength), as well as the overall reliability of the system. For example, you might use the times-to-failure data of a product as strength data and the customer usage data of the product as stress data. You can then use the Stress-Strength Wizard to determine the reliability of the product with regard to how customers use it.

Weibull++ includes both tools:

  • To open the Comparison Wizard, choose Tools > Tests of Comparison.

  • To open the Stress-Strength Wizard, choose Tools > Stress-Strength Calculations.

To compare data sets, do the following:

  • Open the window, select two calculated data sheets, and then click Compare. Weibull++ compares the distributions/parameters fitted to both data sets and displays the results. For example, the results from the Comparison Wizard look like this:

  • While the results from the Stress-Strength Wizard look like this:

ALTA also includes the Comparison Wizard tool. In ALTA, the comparison is based on the expected times-to-failure for the extrapolated use-stress level conditions.

To compare the data sets, do the following:

  • Choose Tools > Tests of Comparison. Select two calculated data sheets, and then click Compare. ALTA compares the distribution/parameters that have been extrapolated to the use-stress level for both data sets and displays the results.