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Watchdog technology is often used in electronic technology, not only PLC, but also microcontrollers. The role is not negligible.
The watchdog is actually a system watchdog timer that monitors the scan time of the PLC.
We all know that the working principle of the PLC program uses a circular scanning working mechanism, and each cycle must have a time, which is the scanning time.
Scanning time is limited. It can't exceed this limit. Once the limit is exceeded, it indicates that there is a problem with the scanning mechanism of the PLC. The problem is generally that the user is legally unreasonable when programming. In this case, the alarm must be stopped. What to monitor is the scan time monitor, a system timer, commonly known as the "watchdog."
Once the watchdog acts, the result is a PLC shutdown alarm.