Performing Predecessor Analysis
The Predecessor pane is shown only when the 217Plus or PRISM model is selected. To perform predecessor analysis, you must complete this pane in two different System files. For more information, see Predecessor Pane.
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To use predecessor analysis with another supported model, temporarily switch the model selected in the assembly’s Calculation Data pane to 217Plus or PRISM so that the Predecessor pane is shown. After supplying the parameters required for predecessor analysis in this pane, in the Calculation Data pane, switch back to the original model selection.
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1. To specify the field failure rate information for the predecessor assembly, do the following: a.
a. Open the System file containing the predecessor system or assembly.
b. In the System Tree Items table, select the predecessor assembly. If the entire system is the predecessor assembly, select the top-most assembly. If a lower level assembly is the predecessor assembly, select that assembly.
c. Select the Predecessor pane. No predecessor assembly should be selected. If this is the case, the last two fields are available.
d. For Number of hours, enter the total number of hours in which the assembly operated in the field.
e. For Number of failures, enter the number of failures observed for the assembly during the specified operating time.
f. Run prediction calculations. For more information, see Calculating Prediction Results.
g. When finished, close the System file.
2. To specify that predecessor assembly with the field failure rate information to use to adjust the base failure rate for the new assembly, do the following:
a. Open the System file containing the new system or assembly.
b. In the System Tree Items table, select the new assembly. If the entire system is the new assembly, select the top-most assembly. If a lower level assembly is the new assembly, select that assembly.
c. Select the Predecessor pane.
d. Click the browse button for Predecessor Information to open the window for selecting the System file, configuration, and assembly.
e. Complete this window by selecting the System file, configuration, and assembly for which you entered field failure information in step 1.
Predecessor failure rate, Predecessor number of hours, and Predecessor number of failures, which are display-only, now show the predicted failure rate, number of operating hours in the field, and number of failures during this period for the predecessor assembly.
When you run prediction calculations in the System file that contains the new assembly, the display-only values in the Predecessor pane are used to adjust the base failure rate calculated by the selected model. If predecessor and Bayesian analysis are both performed on the same assembly, predecessor calculations are performed before Bayesian calculations. For more information, see Failure Rate Adjustments.
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The failure rate unit for the PRISM model is failures per million calendar hours. If PRISM is the model selected for the new assembly, you may need to convert the failure rate predicted for the predecessor assembly from failures per million operating hours to failures per million calendar hours. This can be done by multiplying the operating hour failure rate by the ratio of operating hours to total calendar hours.
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