Back to FBD referenceTypical FBD symbol for CTU
Counters
CTU
Count-up counter
The CTU block increments an internal counter on rising edges of CU. When R is active, the counter resets to 0.
Typical FBD symbol
CU
R
CTU
Q
Inputs
| Name | Type | Required | Description |
|---|---|---|---|
| CU | BOOL | Yes | Count-up input. Rising edges are counted. |
| R | BOOL | Yes | Reset current count to 0. |
Outputs
| Name | Type | Required | Description |
|---|---|---|---|
| Q | BOOL | Yes | TRUE when count has reached PV. |
Parameters
| Name | Type | Required | Default | Description |
|---|---|---|---|---|
| PV | number | No | 1 | Preset count value. |
Stateful
Yes, the block keeps internal state between scans.
Behavior rule
Counts rising edges on CU; when R = TRUE resets count to 0; Q = TRUE when count >= PV.
Practical use
- stop a conveyor after counting the required number of boxes.
What to watch
- Keeping CU constantly TRUE and expecting a count on every scan. CTU counts signal edges.
- Confusing CTU reset with CTD reset: CTU R returns the count to 0.