Generic OPC syntax

The Communication Driver serves as a container for the OPC Groups, which provide the mechanism for containing and logically organizing OPC items. Within each OPC Group, an OPC-compliant client can register OPC items, which represent connections to devices in the field device. In other words, all access to OPC items is maintained through the OPC Group.

The fully qualified name for an OPC item is called the Item ID (equivalent to Item Name). The syntax for specifying a unique Item ID is Communication Driver-dependent. In OPC Communication Driver, the syntax can be as follows:

AREA10.VESSEL1.TIC1.PLC.400001

where each component (delimited by a period) represents a branch or leaf of the field device’s hierarchy.

In this example:

• AREA10.VESSEL1.TIC1 is the link name

• PLC is the name of the target PLC

• 400001 is the specific data point (Item) desired.

  • An item is typically a single value such as an analog, digital, or string value.

The Item ID describes the syntax for defining the desired data point, and Access Path defines optional specifications for obtaining that data.

In Communication Drivers, the Access Paths are equivalent to Device Groups. It defines the update interval between the Communication Driver and the field device for accessing the values of data points in the PLC.