Setting the Operation Properties for an FMRA

Before you perform analytical calculations or simulations in the FMRA, make sure you at least specify the operating time for the top-level item. If applicable, you can also specify other operation properties at the individual item level.

These properties are located under the Operation heading when you select an item in the FMRA in XFMEA/RCM++.

  • Operating Time: The amount of time for which the system is expected to operate (and the time for which the results are estimated). This can be modified at the system level only. When you perform a simulation-based calculation, you can also edit this value in the simulation settings window.
  • Current Age: The age of the item at the start of the analysis. This allows you to define items that have already accumulated age prior to the start of the current mission (i.e., used components). When you add a new item to the system hierarchy, it will inherit this value from its immediate parent. If you change this value for an item, you will be given the option to make the change for just the selected item, or for the item and its dependents (provided that you have write permission for all items that would be affected, and that none of the items are currently in use by another user). This option will be given even in cases where the reliability is defined at the current item's level; if you choose to make the change to dependents, the value will be applied underlyingly even though it will not be used for calculations.
  • Qty: The number of identical sub-items represented. This property allows you to represent multiple copies of the same item with the same properties without having to create individual items (e.g., the 4 tires on a car). A value greater than 1 in this field will cause the item to be represented in the FMRA Diagram as a multi block. By default, the multi block will be configured so that the items are connected in series, but you can manually change this to a parallel configuration. (For more information on multi blocks, see Standard Blocks and Basic Configuration in the BlockSim documentation.) This value is taken into account at all levels for FMRA calculations performed in XFMEA/RCM++; it does not apply at the system level in FMRA calculations in BlockSim.

IMPORTANT: In versions prior to Version 2020, the Qty value was not taken into account in FMRA simulation results in BlockSim. Resimulating an FMRA with Qty values other than 1 in Version 2020 or later will cause BlockSim simulation results to change.

  • Duty Cycle: Allows you to model situations where the actual usage during system operation is not identical to the usage for which you have data (either from testing or from the field). This can include situations where the item:
    • Does not operate continuously (e.g., a DVD drive that was tested in continuous operation, but in actual use within a computer accumulates only 18 minutes of usage for every hour the computer operates).
    • Is subjected to loads that are greater than or less than the rated loads (e.g., a motor that is rated to operate at 1,000 rpm but is being used at 800 rpm).
    • Is affected by changes in environmental stress (e.g., a laptop computer that is typically used indoors at room temperature, but is being used outdoors in tropical conditions).

In these cases, continuous operation at the rated load is considered to be a duty cycle of 1. Any other level of usage is expressed as a percentage of the rated load value or operating time. For example, consider the DVD drive mentioned above; its duty cycle value would be 18 min / 60 min = 0.3. A duty cycle value higher than 1 indicates a load in excess of the rated value.

If a duty cycle is specified for a subsystem or item, it specifies the percentage of operation as relates to the parent item. That is, the effects of the duty cycle for a parent item and the duty cycle for a sub-item are compounded. For instance, if a system has a duty cycle of 2 and its subsystem has a duty cycle of 0.3, the effective duty cycle for the subsystem would be 2 x 0.3 = 0.6, or about 2/3 the rated load value or operating time.

The ReliaWiki resource portal has more information on duty cycles at: http://www.reliawiki.org/index.php/Time-Dependent_System_Reliability_(Analytical).

  • Maintenance Group: Allows you to model situations in which some event within the group can trigger maintenance for other items(s). This field is applicable only for FMRA simulations in RCM++, and it considers system hierarchy items only.

Note: Maintenance groups defined for top-level systems in RCM++ will not transfer to FMRA diagrams in BlockSim if you use FMRA synchronization. Similarly, maintenance groups defined for FMEA records in BlockSim's diagrams will not transfer to RCM++. This is because the applications use different structures to represent the FMRA hierarchy.

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