ScanTime is defined as the time required for one full cycle of a PLC.

• A. The time to scan inputs only
• B. The time for one full cycle
• C. The time to boot the controller
• D. The time to update outputs

Answer: (B)

Scan time is the time it takes to complete one full PLC cycle, which includes reading inputs, executing the program logic, and updating outputs. It’s not merely the time to scan inputs or just the time to update outputs, because a complete cycle encompasses all three stages plus any additional housekeeping during that cycle. Booting the controller is a separate startup process, not part of the regular scan. Understanding scan time helps you gauge how quickly the PLC can react to changes—the shorter the scan time, the faster the control loop can respond.