Industrial Engineer · phase 1 of 16
Watchdog Timer
Diagnostic timer that faults or resets the controller when program execution exceeds an allowed time or stops responding.
The Explain card
- Plain English
- The watchdog is a timer the controller resets every scan. If a scan takes too long or the program stops responding, the timer runs out and the controller faults rather than running blind.
- Example
- A loop in structured text never exits. The scan runs past its limit, the watchdog trips, and the outputs go to their safe state instead of holding the last command forever.
- Why it matters
- A controller that hangs with outputs frozen on is a machine nobody is driving. The watchdog turns that into a visible fault with a timestamp in the log.
- Hook
- The dog barks when the program stops walking it.
Where it sits in the deck
Phase 1: PLC Controller Hardware
The box itself, from processor and rack to the modules that plug into it, because nothing else in the deck lands until you know what a PLC physically is.
