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	Tasks

Task Scheduling

The following information applies to the task scheduling properties for preventive tasks, inspection tasks and the inspection portion of on condition tasks.

Click the arrow in the When is this task performed? field to define the criteria for performing the task. The remaining fields in the task scheduling properties will depend on your selection in this field. The task can be performed:

At certain intervals. If you select this option, you must then specify:
- Whether the interval is fixed or dynamic.
- Whether the interval is based on the item’s age or on calendar time.
Upon certain events. If you select this option, you can choose for the task to be performed:
- Whenever the system is down for any reason. No further task scheduling properties are required for this option.
- Based on events in a maintenance group. The task will be performed when user-specified events occur in one or more user-specified maintenance groups. The item that the task is assigned to does not need to be part of the selected maintenance group(s).
- When a maintenance phase in a BlockSim phase diagram starts. This option should be used only if simulation will be performed in BlockSim, via a phase diagram; if a task is scheduled to be performed upon the start of a maintenance phase and there is no maintenance phase, the task will never be performed.

The remaining task scheduling properties for each type of schedule are given next. For any interval that you specify, you will be asked to specify the time units used.

Fixed interval based on either item age or calendar time: Enter the interval when the task will be performed (e.g., if you enter 100, the task will be scheduled for 100, 200, 300, etc.).
- Item age refers to the accumulated age of the block, which gets adjusted each time the block is repaired (i.e., restored). If the block is repaired at least once during the simulation, this will be different from the elapsed simulation time. For example, if the restoration factor is 1 (i.e., "as good as new") and the assigned interval is 100 days based on item age, then the task will be scheduled to be performed for the first time at 100 days of elapsed simulation time. However, if the block fails at 85 days and it takes 5 days to complete the repair, then the block will be fully restored at 90 days and its accumulated age will be reset to 0 at that point. Therefore, if another failure does not occur in the meantime, the task will be performed for the first time 100 days later at 190 days of elapsed simulation time.

- Calendar time refers to the elapsed simulation time. If the assigned interval is 100 days based on calendar time, then the task will be performed for the first time at 100 days of elapsed simulation time, for the second time at 200 days of elapsed simulation time and so on, regardless of whether the block fails and gets repaired correctively between those times.

If the task is performed at fixed intervals, you can select the Override task scheduling properties with a task package option to assign the task to a task package, which is a group of tasks that are performed together at scheduled intervals.

Dynamic interval based on either item age or calendar time: The task will be performed at variable user-specified intervals. This can be used, for example, to schedule maintenance to be performed with increasing frequency as an item gets older. The Dynamic Intervals field shows the number of intervals specified. Click the button (...) to open the Intervals window, which allows you to enter the item age intervals when the task will be performed. The intervals are the actual time between maintenance (i.e., they are not cumulative).
Based on events in a maintenance group: Specify the events that can trigger the task (i.e., a component fails; a corrective, preventive or inspection task starts; a component is restored to operation), and choose the maintenance group(s) in which the event(s) must occur in order to trigger the task.

Note: If a task has been assigned to a task package, either by the Override task scheduling properties with a task package property mentioned above or via the Scheduled Task Packaging window, the task scheduling properties will be disabled and displayed in italics.