Warranty Analysis Plots

The features on the plot sheet of warranty analysis folios are similar to the options available for all other Weibull++ plots. Features that are not applicable to warranty analysis will be hidden or disabled.

In addition to the standard plots in Weibull++, the following plot types are available for warranty analysis:

  • Expected Failures plot is available only when you've generated forecast data. It shows the expected number of failures over a period of time. Four additional options in the control panel are associated with this plot:
    • Cumulative Failures shows the cumulative percentage of failures for each time period. For example, consider 10 units that had failed within a period of 6 months. If 2 units failed during the 1st month, then the percentage of failures is 2/10 = 20%. If 3 more units failed during the 2nd month, then the cumulative percentage of failures is (2+3)/10 = 50%, and so on.
    • Failures in Percents shows the percentage of failures for each time period, with respect to the number of units that are still out in the field operating at the beginning of each period.

Note: If you select both the Cumulative Failures and the Failures in Percents options, then the plot will show the percentage of parts failed relative to the number of items still in the field at the time the forecasting began.

    • Show Confidence Bounds shows the upper and lower confidence bounds on the plot.
    • Include Total Data is available only when the Use Subsets check box was selected on the Main page of the control panel. It shows a plot of the entire data set, along with the selected subsets. This allows you to view the overall trend of the entire data set in addition to the trends exhibited by each subset of data.
  • Chi-Squared Sales and Chi-Squared Returns plot types are available only when using the statistical process control (SPC) feature of the Nevada chart format. These plots give a visual indication of whether the expected number of warranty returns for a certain period is within or outside an expected range.

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