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FTA Table Fields
The Table Format file for the FTA Table determines the data fields that appear. The following table describes the fields that are shown by default. For more information, see Table Format Files.
Field
Description
Identifier
The unique identifier assigned to the gate or event. The formats for gate and event identifiers are specified by Identifiers > FTA Event Identifier and Identifiers > FTA Gate Identifier in the System file properties. You can change the gate or event identifier that is automatically assigned. You can also globally renumber gate and/or event identifiers as described in Renumbering Fault Trees.
Gate/Event Type
The type assigned to the gate or event. You can select a different type in this field. Only choices that are valid for selection are available. For inputs to a spare gate, this field is display-only because only spare events can be inputs.
Description
The description assigned to the gate or event.
Logical Condition
The Boolean logic operator (gate) that links the various branches of the tree together and determines whether the top event can occur. Choices are Normal, True, and False.
The remaining fields are display-only. They are completed only when the parameter definition for the event is User-Defined. All of the values that are shown in these fields are entered on the Calculation Data page in the Properties window for the event. For more information, see Gate or Event Properties.
Model
The model to use to calculate the failure rate for the event. The models available depend on the FTA calculation type. For more information, see:
Failure Rate Type
Indicates the type of failure data available for the event. For all models that require the entry of failure data, choices are Failure Rate or MTBF. For Input Value, you then specify the appropriate failure data.
Exposure Time Percentage
The percentage of the overall mission time specified as the exposure time, or ‘at risk’ time associated with the event. This percentage is the fraction of the mission time for which the event is valid.
Dormancy Factor
The ratio of failure rate in the spare mode and the failure rate in the operational mode for a spare event, which is an input to a spare gate.
• If the dormancy factor of all spares (events) connected to a spare gate are 0, then the spare acts like a cold spare.
• If the dormancy factor of all spares connected to a spare gate is 1, then the spare acts like a hot spare.
• If the dormancy factor of all spares connected to a spare gate are the same (and are between 0 and 1), then the spare acts like a warm spare.
Failure Rate Percentage
The percentage of the failure rate or MTBF to use for the event.
Input Value
The failure data for the event. This is either a failure rate or MTBF value when Model is set to one of the following:
• Failure rate/MTBF
• Failure with repair
• Failure with periodic inspection
This is the constant probability of failure when Model is set to Constant probability, or it is the frequency of failure when input Model is set to Frequency. Frequency of failure is defined as the number of failures or average number of failures that would occur each hour.
Input Value 2
The MCT (mean corrective time) for an event with Model set to Failure with repair or the inspection time for an event with Model set to Failure with periodic inspection. If you want to specify the precision for this field’s values, you can do so when you select the FTA Table as the table type in the Project’s Data Definition file.
Units
The units for Input Value 2. Units are either Hours (default) or Minutes.
To have different fields appear in the FTA Table, you can modify the default Table Format file for the FTA Table (Table Format (Fault Tree)). This is very easily done using the Format Builder. For more information, see Using the Format Builder to Modify an Enabled Table.