800xA and OPC (DA, HDA, AE)
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Alarm Limits, Instrument Limits etc ARE real time values - they just typically dont change very often. They are ONLY available in the OPC-DA server.
The OPC-AE server contains alarm message strings.
The OPC-HDA server contains ONLY history data. You must configure a "Log Configuration" aspect to create an item in the HDA server. Other properties like object name, description, high low limits alarm limits etc are not available here. ( They are in the OPC-DA server)
The OPC-HDA history server is usefull if you want to pull history data into external systems like OSI-PI, but you also need to combine this data with information from the OPC-DA server.
Have you already tried OPCDA (ID: ABB.AC800MC_OpcDaServer.3)? You can access variables and function block and control module parameters as long as they are not "hidden" through this server.
800xA also comes with a test opc client in which you can see the opc variables availables easily. I am truly sorry that I cannot recall the executable right now, but you can find out in 800xA help.
The availability of alarm and engineering limits through OPC DA depends on the controller (PLC) family in use.
Eg when using 800xA for Advant Master (aka AC400 Connect) most object types exposes attributes like RANGE_MIN, RANGE_MAX, HI_LIM1, LO_LIM1, etc.
When using AC800 Connect similar attributes do exist for most basic object types, but may be hidden if a basic type is encapsulated inside a custom type.
A RealIO variable contain sub attributes like .Forward.Range.Min, etc.
If you need further assistance please tell us what controller and library you are making use of, or turn to your regional ABB support center.