Back to FBD referenceTypical FBD symbol for NOT
Basic logic
NOT
Logical NOT
The NOT block emits the opposite boolean value: TRUE becomes FALSE, and FALSE becomes TRUE.
Typical FBD symbol
IN
NOT
Q
Inputs
| Name | Type | Required | Description |
|---|---|---|---|
| IN | BOOL | Yes | The signal to invert. |
Outputs
| Name | Type | Required | Description |
|---|---|---|---|
| Q | BOOL | Yes | The inverted input value. |
Stateful
No, the block does not keep internal state.
Behavior rule
Q = NOT IN
Truth table
| IN | Q |
|---|---|
| FALSE | TRUE |
| TRUE | FALSE |
Practical use
- inverting a normally-closed signal;
- blocking operation while a fault is active.
What to watch
- Adding too many NOT blocks. Excess inversion often makes diagrams hard to read.