Third party OPC lost connection
Third party OPC running about one year. It started about week ago, randomly on some workplaces we have on scada objects red crosses (bad data). After closing and opening new screen everything works fine sometimes for few days , sometimes for 20 min. It seem like some short connection lost. Please advice there to start troubleshooting.
If the third party OPC data return by simply cycling the process graphic display the problem is likely in the source OPC server.
To comply with the OPC DA specification, a server must continue updating all clients until they have cancelled their subscriptions.
In System 800xA, each client (=workplace, faceplate, history log, etc.) adds their private and dedicated subscriptions to the source OPC server. There is no piggyback riding on any other subscriber. A subscription is kept running until the client disconnect, e.g. close the faceplate or an admin stop the historian services.
The OPC DA specification does not leave any room for a server to "forget" something a client once added. A server with "amnesia" is violating the OPC specification and should be reported to the vendor if the server program.
The problem is aggravated of the OPC DA standard itself, it is perfectly OK for a server to never call back to the client with data, e.g. a digital signal for an emergency stop. The client adds the item, gets the immediate response and may thereafter wait perpetually for the digital signall to change (which may never happen if the emergency stop never takes place). A client can ask for "Refresh", but this must not be the general case, rather an exception to the rule of that a server must continue updating all clients until they cancel their subscriptions. System 800xA does not automatically refresh OPC DA subscriptions, even if there has been no response on a long while.
The OPC DA Connector service and associated OPC Adapter DLL are packed with logging that can be used indicate what is made and what is returned when interacting with any OPC server connected to System 800xA.
The logs reside within a less documented and unofficial tool of System 800xA called Applog.
- Please read the attached document
- Enable the connector and adapter's Basic logs to level 3
- Study the printouts
- Consider enabling the Save log output to file... checkbox for continuous logging (if not enabled, logs wrap in circular buffers of the applog service)
- Consider using a LogInit if you want to make sure logging continues even after a reboot of the computer or OPC DA Connector
- Applog is decentralized. Logging and viewing of logs does not have to take place on the same node. I.e. you can "Log there, but view here"
The basic calls for subscribing is AddGroup and AddItems. There are equivalents to cancel a subscription, RemoveGroup and RemoveItems.
In later versions of 800xA, the data callbacks from the OPC server can be studied in the log called DataChanged, in earlier versions it was embedded into the two Basic logs.
Please consider filing a support case with your regional ABB support center to obtain professional assistance. My liberty at this open Internet forum is limited.