There are many PLC self-test signals and many internal devices, and most users do not give full play to their functions.
In fact, it can be used to monitor the work of the PLC itself, or to monitor the control object.
Here is an idea of using a PLC timer as a watchdog to monitor the working conditions of the control object.
If the PLC is used to control the action of a moving part, to see if the action is carried out after the control is applied, the watchdog method can be used to monitor it. This is done by allowing the watchdog timer to count while control is being applied. If the action is completed within the specified time, that is, when the timer does not exceed the warning value, and the action completion signal has been received, it means that the control object is working normally and no alarm is required.
If it times out, it means that it is not normal and can be dealt with accordingly.
If all the important control links of the control object are “watched” by such watchdogs, then the work of the system will be well known. If there is a problem, it is easy to find out what link is stuck.
There are other monitoring jobs that can be done. For a complex control system, especially an automatic control system, it is very necessary to monitor and even further self-diagnosis. It can reduce the faults of the system, it is easy to find the faults, it can improve the cumulative average trouble-free running time, reduce the fault repair time, and improve the reliability of the system.
