Performing a Reliability Allocation
As described in
Reliability Allocation, a reliability allocation allows you to allocate a failure rate, MTBF, reliability, or availability goal to an assembly, and then, based on parameters for the chosen allocation method, calculate an allocated failure rate for its child items (subassemblies and/or parts). For more information, see
Reliability Allocation Calculations.
1. Under
Prediction in the
System file properties, ensure that the desired allocation method is selected for
Allocation method. For more information, see
Prediction System File Properties.
2. To indicate that the failure rate type for an assembly is allocated, do the following:
a. In the System Tree Items table, select the assembly.
b. Select the Calculation Data pane.
c. For Failure rate type, select Allocated. This causes the Allocation pane for the selected allocation method to show.
d. Select the Allocation pane.
e. For Allocation action, select Specify Goal so that you can specify the desired goal for the assembly.
For all but the AGREE or repairable system method, Allocation goal type becomes available. Select either Failure Rate or MTBF. Depending on your selection, Allocated goal, FR or Allocated goal, MTBF becomes available. Enter the desired goal.
For the AGREE method, Allocated mission time and Allocated goal, reliability become available. Enter the desired mission time and reliability goal.
For the repairable system method, Availability, Allocated becomes available. MTTR Specified is display-only. For this method, the MTTR (mean time to repair) values for parts are used in place of weight factors.
For the ARNIC, equal apportionment by components, and repairable system methods, no additional parameters are required for lower-level items.
3. For the allocation methods that do require you to enter additional parameters for subassemblies, do the following for each subassembly:
a. In the System Tree Items table, select the subassembly.
b. Select the Calculation Data pane.
c. For Failure rate type, select Allocated. The Allocation pane for the selected allocation method shows.
d. Select the Allocation pane.
e. For Allocation action, select Perform Allocation so that you can enter the parameters required by the selected allocation method for this subassembly.
For the base, non-normalized method and base, normalized method, Allocation weight factor becomes available. Enter the appropriate value.
For the AGREE method, Allocation, mission time and Allocation importance factor become available. Enter the desired mission time and appropriate importance factor.
For the feasibility of objectives method, the following parameters become available: Allocation, Environment; Allocation, Intricacy; Allocation, Performance Time; and Allocation, State of the Art. Select the appropriate values.
Only the base, non-normalized and base, normalized methods provide for entering weight factors at the part level. For the AGREE and feasibility of objectives method, the allocated failure rate for a part is always 0.
4. For the base, non-normalized or base, normalized method, for each part, do the following to enter parameters:
a. In the System Tree Items table or the Parts Table, select the part.
b. Select the General Data pane.
c. For Failure rate type, select Allocated. This Allocation pane for the part shows.
d. Select the Allocation pane.
e. For Allocation weight factor, enter the appropriate value.
5. Run prediction calculations, ensuring that
Allocations is selected on the
Prediction Calculations page in the
Calculate window. For more information, see
Calculating Prediction Results.
Once allocation calculations run, allocations for each assembly and/or part display as failure rates.