In the base, normalized allocation method, you enter the desired failure rate for a particular assembly as either a failure rate or MTBF goal. You then assign a weight factor between 0 and 1 to each subassembly and/or part. The total of the weight factors for all child records of a system tree item should equal 1, although this is not enforced.

When allocation calculations run, failure rates are allocated based on weight factor percentages. If a weight factor for an item is less than 0 or greater than 1, a warning message is shown with the results once the allocation calculations finish. In such situations, the allocated failure rate for this item is set to 0.

If an allocation method that accepts weight factors outside of the 0 to 1 range is initially selected but is then changed to this allocation method, you should change all weight factors to values between 0 and 1. Otherwise, once allocation calculations finish, warnings appear in the results for items with inappropriate weight factors, and the allocated failure rates for these items are set to 0.

Assume that you have a multilevel System Tree and want to enter a failure rate goal for the system and allocations for two subsystems and several assemblies as follows:

System Failure Rate Goal: 1000 FITs

A = 60% of the system = 600 FITs

B = 40% of the system = 400 FITs

A1 = 50% of Subsystem A = 300

A2 = 50% of Subsystem A = 300

B1 = 75% of Subsystem B = 300

B2 = 25% of Subsystem B = 100

The System Tree for this scenario would look like this:

System (1000)

Subsystem A (60%)

Assembly A1 (50%)

Assembly A2 (50%)

Subsystem B (40%)

Assembly B1 (75%)

Assembly B2 (25%)

For the top-most assembly (system), you enter a failure rate goal of 1000 in the assembly’s Allocation pane. For more information, see Base Allocation Method. For subsystems A and B, you enter weight factors of 0.6 and 0.4 respectively in their Allocation panes. For both assemblies A1 and A2, you enter a weight factor of 0.5 in their Allocation panes. Finally, for assemblies B1 and B2, you enter weight factors of 0.75 and 0.25 respectively in their Allocation panes. Therefore, the failure rate for assembly B2 is 25% of the failure rate for subsystem B. The failure rate for subsystem B is 40% of the total system failure.

If parts were included in this example, you assign a weight factor in the Allocation pane for each part. For more information, see Allocation Pane (Part).