Summary

• The PI Interface for OPC DA uses a custom exception reporting mechanism for advise and event points. Specifically, when it has been longer than ExcMax since the interface last received an update from the OPC server, it sends the previous value again with a new timestamp.

• This exception value does not represent a real interaction with the OPC server.

• Users who require true readings should configure polled rather than advise or event points. Alternatively, they should set ExcMax to zero to turn off exception reporting altogether.

To reduce the likelihood of recording inaccurate data, users should at the very least set ExcMax larger than the update rate.