Industrial Engineer · phase 3 of 16
Scan Time
Elapsed time required for one controller execution cycle or one scheduled task pass.
The Explain card
- Plain English
- Scan time is how long one pass through the cycle takes. It goes up with more logic, more I/O, more network traffic and heavier instructions.
- Example
- A controller shows a scan time of 8 milliseconds with a maximum of 23. The maximum is the number that matters, because that is the pass where the input got missed.
- Why it matters
- A scan that grows past the watchdog faults the controller, and a scan that grows past a sensor's pulse width loses counts. Watch the maximum in the controller properties after every significant edit.
- Hook
- The machine can only react as fast as it can think.
Where it sits in the deck
Phase 3: PLC Program Organization and Execution
How the logic is arranged and how the scan actually runs it, which is the difference between code that works and code that works every time.
