I would like to create a notification if a PLC is not available but the OPC is ok, I am thinking to check the PIPoint quality, however I have no idea how to read it to create a logic in PI AF and notification.
Like this Qualities.
A few options:
PI Interface for OPC DA stores either the quality or the value in a PI point, whereas the OPC server returns value and quality in separate fields. If a value is good, it is stored in the point. If a value is bad, a digital state that describes the quality is stored. For questionable-quality data, you can configure the interface to treat the values as good and store them, or treat them as bad and store a digital state. You cannot configure the interface to store a bad-quality value. To configure handling of questionable-quality data using PI ICU, go to the OPCInt > OPC Server page and enable the desired option, as shown in the following figure.
I would suggest reviewing Data quality information section in the User Guide, I'm sure it will answer your question.
Not always an option, but the ideal situation is to create a heartbeat tag on the PLC itself and then monitor it's associated PI tag's freshness in a notification. Then you are assuring you have data flow from the PLC > OPC Server > OPC interface > PI DA.
If this is not possible, monitor a "busy" PLC field tag.
To follow up on Brian's suggestion, I have had success using the seconds or minutes component of the PLC system clock for use as a heartbeat.
Retrieving data ...