Flow Ctrl Tech Engineering

Optimizing PLC Scan Times & Eliminating Watchdog Timer Major Faults

How to profile cycle execution times, break up blocking FOR loops, optimize communications overhead, and avoid catastrophic CPU watchdog timer trips.

  • The watchdog timer is a hardware circuit that resets the controller if the scan cycle exceeds a preset ceiling (typically 100–500ms).
  • Never execute open-ended WHILE loops in PLC logic; use finite state steps distributed over multiple scans.
  • Limit asynchronous SCADA polling queries to prevent communications tasks from starving the main logic scan.

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