Scan groups and the OPCClient object

A scan group, or device group, is a collection of attributes that have a common update interval. When you configure the OPCClient object, you will need to specify at least one scan group in order to deploy the object. Within each scan group, you can specify data items to use as the object attributes. At runtime, items for a scan group will be updated with the latest values from the OPC communications driver according to the update interval.

From other objects and from scripts, you can reference the attributes (items) you configured for the OPCClient object. For example, you might configure the input source for a FieldReference object to reference an item for one of the scan groups. Thus, the FieldReference object input source would be receiving data from an OPC communications driver via the OPCClient object.

Tip You can use any OPC client tool to browse a field device's address space for item names.

The reference syntax for a OPCClient object data point is:

<objectname>.<scangroupname>.<itemname>

The <objectname> is the name that you choose to give to the OPCClient object.

The value of <itemname> depends on the type of OPC communications driver you are connecting to. For information on how to reference data points in the OPC communications driver, see the driver documentation.

Runtime object attributes allow you to monitor errors related to the data quality for item values in a scan group.