When a reliability element is initially created, the Operating Requirements logic tree will have two AND-Gates (one for External Requirements and one for Internal Requirements). The External Requirements AND-Gate will be empty, and the Internal Requirements AND-Gate will include a Not node referencing the default failure mode for the element:
The External Requirements AND-Gate can be used to reference conditions/requirements outside the element, while the Internal Requirements AND-Gate can be used can be used to reference child elements and conditions (such as the status of a failure mode).
A logic tree consists of two types of nodes: gate nodes and variable nodes.
Gate nodes are used to construct the logical framework of the tree. Gate nodes require "child nodes" that are either other gate nodes or variable nodes.
There are three types of gate nodes:
AND-Gate. An AND-Gate is true when all of its child nodes are true. The child nodes can be variable nodes, or other gate nodes.
OR-Gate. An OR-Gate is true when at least one of its child nodes is true. The child nodes can be variable nodes, or other gate nodes.
N-Vote Gate. An N-Vote Gate is true when N (which is user-specified) or more of its inputs are true. The child nodes can be variable nodes, or other gate nodes.
There are four types of variable nodes, each of which requires an input:
Condition. A Condition node is true when the specified condition evaluates to true. The input must be a Condition output or a conditional expression. The Condition node is often used to reference the status of the element or a failure mode.
Not. A Not node is true when the specified condition evaluates to false. The input must be a Condition output or a conditional expression. The Not node is most commonly used to reference the status of the element’s failure modes.
RL Component. An RL Component node is true when the referenced reliability element is operating (when referencing reliability element as an External Requirement) or capable of operating (when referencing a child reliability element as an Internal Requirement).
Not RL Component. A Not RL Component node is true when the referenced reliability element is not operating (when referencing a reliability element as an External Requirement) or not capable of operating (when referencing a child reliability element as an Internal Requirement).
Clicking the Add button displays a menu which allows you to select the desired node type:
When adding a variable node, a dialog will be displayed for defining the input to the node.
Where the new node will appear is determined by the type of node that is selected prior to pressing the Add button:
•If a gate node is selected prior to pressing the Add button, the new node will appear as child node to the selected gate node:
In this example, the External Requirement AND-Gate was selected when an AND-Gate was added. The AND-Gate is therefore added as a child node to the External Requirements node.
•If a variable node is selected prior to pressing the Add button, the new node will appear as child node to the selected node’s parent:
In this example, a Not Condition node (the default Not node referencing the default failure mode) was selected when an AND-Gate was added. The AND-Gate is therefore added to the parent of the Condition node.
GoldSim allows you to automatically convert from one logic-tree type to another. The automatic conversion is carried out as follows:
|
Original Node… |
Is converted to this |
|
Condition |
Not |
|
Not |
Condition |
|
AND-Gate |
OR-Gate |
|
OR-Gate |
AND-Gate |
|
N-Vote Gate (N or more must be true) |
N-Vote Gate (total child nodes – N + 1 or more must be true) |
|
RL Component |
Not RL Component |
|
Not RL Component |
RL Component |
Adding and using AND and OR Gates is straightforward. Use of the other nodes is described in more detail in the topics below.
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