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Test Design Assistant

Expected Failure Time Plot Example

Expected Failure Time Plot

The Expected Failure Time plot provides a visual depiction of what failure times you can expect to observe when you implement a particular test plan. If you perform the test and enter the actual failures as they’re observed, you can use the plot to monitor whether the test is proceeding as planned, which could provide an early warning that adjustments may be needed. The ReliaWiki resource portal has more information on the Expected Failure Time Plot at: http://www.ReliaWiki.org/index.php/Reliability Test Design.

Tip: You can also use this plot to determine whether a specified reliability demonstration test will exceed the allowable number of failures. For example, if you have designed a zero-failure test and wish to determine whether zero failures will occur during the test, you could examine the lower confidence bound of the first predicted failure for that test. This information will help you determine whether a failure is likely to occur before the end of the test.

Generating an Expected Failure Time Plot

Follow the steps outlined below to generate an Expected Failure Time plot.

Note: You can also get the parameters and time units from a calculated data sheet in the current project by clicking the Get Failure Model icon on the control panel. After you select the data sheet, click the Redraw Plot icon to generate the plot.

The three vertical tick marks on each line display the lower confidence bound, median value and upper confidence bound for the expected failure time of a tested unit.

Tip: If you have a column of data copied to the Clipboard (e.g., from a data sheet), you can click the Clipboard icon at the top of the Time column to paste the data into the table.

You can view a calculated value by pointing to the relevant vertical tick mark on the plot. Alternatively, click Results (...) in the Expected Failure Time area of the control panel to view all calculated values at once.

Additional Control Panel Options

The control panel also includes the following options:

 

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