Fault Tree Gates


There are three types of gates: AND gates, OR gates, and NOT gates.

AND and OR Gates

All binary events in a fault tree are connected by AND gates, OR gates, and/or user-defined modules. Gates are nodes that are binary event operators with at least one input and a single output. The gates act on binary events that are attached to it and produce a probability output. In a fault tree, gates are always oriented such that they take input from below and produce an output above.

Adding AND and OR Gates

  • Click on FAULT TREE | Gate | AND or OR on the ribbon ( and , respectively). The mouse cursor changes to indicate the type of gate you are adding.
  • Click in the fault tree where you would like the gate placed.
  • Note: if you click on another node a connection will be drawn from the gate to the node.
Connecting AND and OR Gates to Binary Events

  • Click on FAULT TREE | Connection | Add. The cursor changes to the begin connection cursor.
  • Click on the event that is the predecessor to the connection. The cursor changes to the finish connection cursor.
  • Click on the gate to finalize the connection of the event to the gate.

Note the output of a gate can also be the input to an event. To connect two nodes in this manner, you'd click the gate first and then the event.

Deleting AND and OR Gates

  • Click on the gate.
  • Press the Delete key.

Note all the connections going into and out of the gate will also be deleted.

NOT Gates

The binary event operator NOT takes only one input event and produces a binary event that occurs when the input event does not occur. NOT gates are specified directly on connections. In order to create a NOT gate, you must first create a connection between two events.

Adding/Removing a NOT Gate

  • Click on the desired connection.
  • Click on FAULT TREE | Connection | NOT ().
If a NOT gate did not exist, DPL creates one and draws a blue triangle on the connection. If a NOT gate existed, DPL removes it.

Miniature NOT Gates

By default, DPL displays NOT gates as blue triangles on connections. If you have a large number of NOT gates, this can take up a lot of screen space. To have DPL display NOT gates as small blue circles instead, click on FAULT TREE | Display | Mini NOT Gates.

Versions: DPL Fault Tree

See Also


Fault Tree Nodes