Data point groups

All data that should be accessed over an OPC UA client has to be defined within two data point groups. Data point elements (= "items") are assigned via the data point groups OPCUARead(readable),OPCUAWrite (readable and writable), OPCUAAlarm (alarms), OPCUAHARead (historical access) and OPCUAEvent (OPCUA Base Event).

The groups are configured in the WinCC OA system management of the data point groups (see figure below). The WinCC OA OPC UA server reads these groups into its PABB while booting. In the PABB the WinCC OA configs _online and _original are used for data values. The WinCC OA config _alert_hdl is used for Alarms&Conditions. The list of all used attributes of the mentioned configs is pointed out in the chapter Assignment of WinCC OA Attributes to OPC UA Attributes.

Figure: WinCC OA data point group management with the data point groups

The data point elements that the server shall pass to the client are defined in these groups.

How to assign data point elements to data point groups is described in the chapter Data point groups.

  • OPCUARead elements are only readable for the client
  • OPCUAWrite elements are readable and writable for the client
  • OPCUAAlarm elements that send an alarm to the client (for further information see chapter Alarms and Conditions).
  • OPCUAHARead elements that define for which of the data point elements assigned to OPCUARead or OPCUAWrite historical values shall be readable (refer to Historical Access for further information).

  • OPCUAEvent elements that define for which dyn_string DPE an OPCUA Base Event is sent.

    OPCUA Base Event:

    Index 0 - Serverity; Value Range: [1,1000]

    Index 1 - Eventtext; Custom String´

All data point elements added to the OPCUARead group are shown together with their values at the client. For elements of the OPCUAWrite group new values can be set or read by the client. If an element is present in both groups, it can only be read.

To enable historical access, the respective data point elements must be defined both in OPCUARead (or OPCUAWrite) as well as OPCUAHARead.

Note that the OPCUARead, OPCUAWrite, OPCUAAlarm and OPCUAHARead groups must not be deleted. In case that one of these groups has been deleted, an alias has to be created for this group. Otherwise the OPC UA server is not able to recognize the group.

Note that the OPCUARead, OPCUAWrite, OPCUAAlarm and OPCUAHARead groups may not contain subgroups. If a subgroup was added to one of these groups an error message is shown and the subgroups will be ignored.

The WinCC OA OPC UA server has a hierarchical structure and allows any clients a hierarchical browsing (see Browsing for Items).

The Config entry nodeIdType allows to enable the server access via DP Alias. Note that every DPE needs an Alias when this entry is set. Otherwise it is not possible to access the server.