Contained Standby Blocks

Add a contained block to a container by selecting the container and then choosing Diagram > Blocks > Add Block.

The properties available for configuring a contained standby block will vary depending on whether it is in an analytical RBD or a simulation RBD. In addition to the common block properties, you will need to describe how the block behaves.

The first step is to assign a URD for the block when it is in an active state and one for when it is in a standby state (i.e., quiescent or dormant). As explained in the topic on standard blocks, each URD uses a failure model to describe the block’s reliability characteristics; for blocks in simulation diagrams, the corrective task and/or scheduled tasks associated with the URD are also applied to the block.

Note: In the case that both quiescent and active failure models are the same, the units are in a simple parallel configuration (also called a hot standby configuration). When the probability of failure of the standby component is less in the quiescent state than in the active state, that is called a warm standby configuration. Lastly, when the probability of failure of the standby component is zero in the quiescent state (i.e., the component cannot fail when in standby), that is called a cold standby configuration.

The following options may be available for contained standby blocks in both analytical and simulation diagrams:

Duty Cycle allows you to model situations where the actual usage of a block 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.

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

Active/Standby allows you to specify whether the block is in an active or standby state at the beginning of the simulation.

Tip: You can quickly change a block's state by selecting or clearing the Diagram > Properties > Standby Settings > Set Block to Active (Not Standby) command.

Supplemental Costs allows you to choose or create models to represent costs that are always associated with the block. Cost per Failure uses a cost model, and Downtime Rate uses a cost per unit time model. If no models are assigned, it is assumed that there are no additional costs.

The following options are available only for contained standby blocks in simulation diagrams:

Reactivate After Repair if selected, the block will return to the active state immediately after it has been repaired. Otherwise, the block will remain in the standby state after if has been repaired and will be switched back to the active state only if and when the contained standby block that was activated in the initial switch fails. This option is available only if the active state is selected.
Operates even if system is down if selected, indicates that the block continues to operate even if the system is not operating. If it is not selected, the block does not continue to accumulate age when the system is down.

In a simulation diagram, you can also assign a maintenance group for the contained standby block. A maintenance group is a set of blocks where some event within the group can trigger either maintenance or state changes for one or more blocks, either within the group or outside of it.

Once the block is configured, you can click the Optimum Replacement icon in the Properties area to open the Optimum Replacement window for the current block; this window allows you to determine the most cost-effective time to replace the component based on costs for planned (i.e., preventive) and unplanned (i.e., corrective) replacement.