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This section is intended to help you identify the basic types of blocks found in fault trees.
Note: The shapes, colors and locations shown here represent the default settings. These settings may be changed via the Diagram Style window and/or the Block Style window.
Visual Indicator |
Block Type |
Description |
In an AND gate, the output event occurs if all input events occur. |
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In an OR gate, the output event occurs if at least one of the input events occurs. |
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In a NOT gate, the output event occurs if the input event does not occur, and vice versa. This gate performs inversion. NOT gates are available only in analytical fault trees. |
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In a NAND gate, the output event occurs if any one of the input events does not occur. NAND gates are available only in analytical fault trees. |
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In a NOR gate, the output event occurs only if none of the input events occur. NOR gates are available only in analytical fault trees. |
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In a Voting OR gate, the output event occurs if some quantity (k) or more of the (n) input events occur. The voting gate is visually distinguished from the OR gate by the k/n value displayed on it. |
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In an Inhibit gate, the output event occurs if all input events occur and an additional conditional event occurs. |
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A standby gate allows you to identify events that operate in a standby configuration. Events that are below a standby gate are dependent events, which describe the characteristics of the items that operate together in the standby configuration. |
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A load sharing gate allows you to identify events that operate in a load sharing configuration. Events that are below a load sharing gate are dependent events, which describe the characteristics of the items that operate together in the load sharing configuration. |
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In a priority AND (PAND) gate, the output event occurs if all input events occur in a specific sequence. |
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In a sequence enforcing (SEQ) gate, events are constrained to occur in a specific sequence and the output event occurs if all input events occur in that specified sequence. |
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Basic Event |
Events are simply representations of some occurrence, typically a failure or error. Different shapes are used to represent different types of events. These shapes convey additional visual information for the analysis but all event types are handled in the same way during analysis or simulation. For information on how these event types are often used, see the topic on fault tree events. |
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Undeveloped Event |
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Trigger Event |
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Resultant Event |
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Conditional Event |
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Subdiagram |
A block that is in the shape of a folder indicates that the block represents an existing diagram. Subdiagrams can be used in fault trees in the same way they are used in RBDs. |
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