Setting Reliability Policies

Before you can perform any calculations with the FMRA, you must choose a reliability policy type for each record in the hierarchy. If you choose the "Inherit" policy type, the record's reliability will depend on the record's dependents. If you choose any other policy type, the record's reliability will depend on the URD that is assigned to it. See Performing Calculations with the FMRA.

Note: The information in this topic assumes that you understand how to configure URDs and use them to define reliability characteristics within Synthesis-enabled applications. If you are not familiar with this concept, see Universal Reliability Definitions (URDs).

Choosing a Type of Reliability Policy

The reliability policy type determines how a record's reliability characteristics will be defined. When you click a record in the FMRA, the Properties tab will allow you to set the reliability policy.

The following policy types may be available under the Reliability Policy heading:

Define at this level: This option is available for all records. When selected, you will be required to set the reliability characteristics of the record by assigning a universal reliability definition (URD) to it. If the record does not yet have an assigned URD, "Default (Not Set)" will show in the Reliability Policy column of the FMRA. The software assumes that items with the default policy never fail (i.e., the reliability is always 100%) and failures with the default policy never occur (i.e., the probability of failure is always 0%).

Note: If you use this option with a record that has dependents, the software will hide those dependents. This is because they will be irrelevant to calculations that you perform with the FMRA.

Inherit: This option is available for all records except causes. When selected, the record will inherit its reliability characteristics from the URDs assigned to its dependents. For example, in the below hierarchy, System 1 inherits its reliability from Cause 1 and SubSystem 2. Thus, the reliability of System 1 is determined by URD_1 and URD_2.

If you calculate the reliability characteristics using Xfmea, the software will assume a reliability-wise series configuration (i.e., it will assume that the occurrence of any cause, or the failure of any sub-item, is sufficient for the entire system to fail). If you have BlockSim 8 installed on your computer, you can also synchronize the FMRA hierarchy with RBDs in BlockSim to arrange the records in a more complex reliability-wise configuration. See Calculation Options Window.

Based on Failure Probability: This option is only available for failure records, and only when the Failure Probability criticality analysis field is enabled for the project. When selected, a probability of failure model (i.e., the probability that the failure mode will occur) will be automatically assigned to the record based on the rating selected in the Failure Probability drop-down list. See Using Rating Scales in the FMRA.
Based on Initial/Revised Occurrence: These options are only available for causes, and only when the Initial Occurrence and/or Revised Occurrence properties are enabled on the FMEA > RPNs page of the interface style. When selected, a probability of failure model (i.e., the probability that the cause will occur) will be automatically assigned to the record based on the rating selected in the Initial Occurrence or Revised Occurrence drop-down list.

To change the policy types of multiple records at once, choose FMRA > Tools > Batch Modify to open the Reliability Policy Update window.

Assigning a Universal Reliability Definition

When Define at this level is selected as the policy type, you will have the option to assign a universal reliability definition (URD) to the selected record. The URD can include a probability model.

When creating a new model for a record, please note the following:

An item's model represents the item's reliability (i.e., the probability that the item will not fail).
A function's model represents the probability that the item will fail to perform its intended function.
A failure's model represents the probability that the failure will occur.
A cause's model represents the probability that the cause will occur.

To edit a record's URD, select the record and then, on the Properties tab, double-click the URD or Model field to open the associated resource wizard.