What is the function of a watchdog timer in a Programmable Logic Controller (PLC) used for power plant automation?

The function of a watchdog timer in a Programmable Logic Controller (PLC) used for power plant automation is to detect and recover from processor or software failures that may cause the PLC to stop executing its program correctly. A watchdog timer is a hardware or software-based timer that must be periodically reset by the PLC program. If the PLC program is running normally, it will reset the watchdog timer at regular intervals, preventing it from timing out. However, if the PLC program crashes, gets stuck in a loop, or otherwise fails to execute properly, it will no longer reset the watchdog timer. When the watchdog timer times out, it triggers a predefined action, such as resetting the PLC, activating an alarm, or switching to a backup control system. This ensures that the PLC does not remain in an undefined or erroneous state, which could lead to equipment damage or unsafe operating conditions. The watchdog timer provides a critical layer of safety and reliability in automated systems, preventing the consequences of PLC failures. It helps to maintain continuous and safe operation of power plant equipment.