OPC Groups

OPC Groups are used to define a set of OPC items which require to be read at the same frequency and with the same trigger method. The OPC items can also be related to each other for the purpose of triggering downstream actions through scripts or calculating formulas, which can only be applied to items within the same group.

Notify Modes

The collection behavior for all OPC items within a group is achieved by setting the appropriate Notify Mode on the group. The available modes are:

  • Group read on timer: Reads all items in the Group at a specified interval. For example, production counters can be collected every 120 seconds.
  • Individual notify: Reads a single item placed in the Group, whenever the value changes, based on the notification from the OPC Server. This mode is used to detect a change in machine status.
  • Group read on notify: Reads all items in the Group, when the value of a designated trigger item change. For example, a set of machine parameters can be captured when a machine stops.
  • Individual write: Writes a value to a single item in the Group. For example, to write master data values to a PLC at the start of a production run or perform interlocking actions.

For notification modes that require periodic polling, an update rate is configured to determine the reading frequency.

Transactional Groups

Once the OPC Client reads data from a group of OPC items, the data is imported into the application. If an import fails for one OPC item, you can control how the remaining items are processed by configuring the Transactional setting. The available options are:

  • On: The entire data import is treated as single transaction. Either all items for the group are successfully stored, or none of the data is stored in the event of one failure
  • Off: Each individual item is treated independently. The failure to import one item does not prevent the successful import of any others in the same group.

History Recording

The OPC Client logs every value read from all OPC Items within a Group to support traceability and troubleshooting. However, History Recording can introduce significant storage and processing overhead groups that collect large volumes of data at high frequencies. Disabling History Recording for these groups can improve performance after data capture has been successfully validated and proven reliable. This setting provides the ability to disable history recordings for applicable groups.