Calculating an Optimal Interval for a Maintenance Task
You can calculate an optimal interval for performing a maintenance task. This is in contrast to specifying an interval for performing the task, which is described in Specifying Task Interval Optimization Parameters.
1. In the RBD Diagram pane, double-click the block to open its Calculation Properties window. For more information, see Block Calculation Properties.
2. On the Maintenance page for the block, do the following:
a. In the Maintenance table at the top of the page, select the task for which to calculate an optimal interval.
For task insertion information, see Inserting Maintenance Tasks for a Block.
b. Beneath the table, click Edit Task. The task’s Maintenance Properties window opens. For more information, see Maintenance Properties.
3. On the Schedule page for the task, do the following:
a. If the block is part of a phase diagram and the task can be performed during maintenance only phases, select Perform during maintenance only phases. This checkbox pertains only to phase diagrams.
b. Select Schedule maintenance. Among the properties made available are Maintenance interval and Units.
c. For Units, indicate whether you want to calculate the optimal number of days in terms of operating days or calendar days.
d. Under Optimize, for Optimization type, select Local or Global.
When Local is selected, the interval for the task is optimized in respect to only this figure and its calculation properties.
When Global is selected, the interval for the task is optimized in respect to the entire system diagram. Both Minimum and Maximum become available so that you can specify the lower and upper limits to use for calculating the optimal interval.
e. If Minimum and Maximum are available, enter the values to use.
The next time that you run RBD calculations, the optimized interval for the task is calculated. Optimized interval, which is display-only, shows the result. Use optimized maintenance interval becomes available so that you can select or clear it to indicate whether you want to use this optimized value when RBD calculations are run again.
4. To specify that an optimal interval is to be calculated for another task, do the following:
a. Use the navigation control at the top of the Maintenance Properties window to select the task.
For information about using this control, see Changing the Active Object in the Properties Window.
b. If a window opens for indicating whether you want to save changes made to the current task, click Yes.
c. For the newly selected task, repeat step 3.
5. Repeat step 4 for each task for which to calculate an optimal interval.
6. When finished, click OK to close the task’s Maintenance Properties window.
7. Click OK to close the block’s Calculation Properties window.
Prior to running RBD calculations, you must ensure that the appropriate values for optimizing task intervals are specified in the Maintenance Interval Optimization Parameters window. For more information, see Maintenance Interval Optimization Parameters window. You can either specify values now or when you next run RBD calculations.
8. To specify values now, see Specifying Task Interval Optimization Parameters.
The next time you run RBD calculations, optimal task intervals are calculated based on values specified for optimization parameters. For more information, see Calculating RBD Results. You can view the optimal interval for a task on the Schedule page in its Maintenance Properties window. For more information, see Schedule Page.
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Optimizations for task intervals are performed for increasing failure rate distributions or when standby failures can be identified only at an inspection. When the failure rate distribution is other than increasing, or when standby failures can be identified in other ways, the value specified for Maximum on the Schedule page in the task’s Maintenance Properties window is used as the optimal inspection interval.
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