Analysis with the Crow Extended - Continuous Evaluation Model

While the Crow Extended model facilitates reliability growth projections, planning and analysis for a single test phase, the Crow Extended – Continuous Evaluation model is designed for analyzing data across up to 10 test phases.

This model provides increased flexibility to analyze data from practical testing situations in which the failure modes may be addressed a) at the time of the failure, b) later in the same test phase, c) between test phases d) during a subsequent test phase or e) after the completion of all test phases.

The continuous evaluation model is available in three Multi-Phase data types: Multi-Phase Failure Times, Multi-Phase Grouped Failure Times and Multi-Phase Mixed data.

The following topics describe how to use the Crow Extended – Continuous Evaluation model in Weibull++, including:

• Using event codes to specify the type of event that each row in the data sheet represents.

• Classifying failure modes according to whether and when fixes will be implemented.

• Setting the effectiveness factors for delayed fixes.

• Analysis results for the continuous evaluation model.

• QCP calculations and plots for the continuous evaluation model.

• Generating an event report for a calculated data set.

• Using the Test for Fix Effectiveness utility to test whether the fixes applied been two test phases have been effective to decrease the failure intensity.

Two related features will be discussed in the next chapter. You can use the growth planning folio to develop the plan for a multi-phase test. Then after you’ve begun to enter the test data into a multi-phase data sheet, you can use a multi-phase plot to link the plan with your test data. The plot provides a visual way to track the progress toward meeting your MTBF goal and determine whether you will need to make adjustments in the remaining test.

For an example that demonstrates how these three tools can be used together, see Example: Multi-Phase Test Planning and Analysis.