Priority AND Gate
The priority AND gate is used to indicate that the output occurs if and only if all input events occur in a particular order. The order of occurrence is the order in which the input events are connected to the priority AND gate from left to right.
The output of a priority AND gate can be the top event or an intermediate event. The inputs can be basic events or outputs of any AND, OR, or dynamic gate. Items need to fail in temporal order from left to right to trigger the event. You can rearrange items that enter priority AND gates by clicking and dragging them to new locations. The priority AND gate also supports a single input. When only a single input exists, the occurrence of that input will trigger the event.
Summary of Logic: All input events must be TRUE for the output to be TRUE, and the events should occur from left to right in the temporal order within the mission time.
A truth table for a priority AND gate follows. In column A, T(1) indicates that the input event occurred first, and T(2) indicates that the input event occurred second. The Boolean equation for a priority AND gate is T = A * B, where A occurs and then B occurs.
|
A
|
B
|
Output
|
|---|---|---|
|
T(1)
|
T(2)
|
T
|
|
T(2)
|
T(1)
|
F
|
|
T
|
F
|
F
|
|
F
|
T
|
F
|
|
F
|
F
|
F
|
Example
For a manufacturing plant to be damaged extensively by fire, the fire alarm must fail, and then a fire must occur in the plant. (If a fire occurs before the fire alarm failure, the damage might be less extensive because the nearby fire department would be notified by the sounding of the fire alarm.)
