Generic OPC syntax

A OI Server 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 OI Server-dependent. In OPC data acquisition OI Servers, 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 for a OI Server.

• 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.

Where Item ID describes the syntax for defining the desired data point, OPC provides for another parameter, called Access Path, that defines optional specifications for obtaining that data.

In OI Servers, Access Paths are equivalent to Device Groups; it is this parameter that is used to define the update interval between the OI Server and the field device for accessing the values of data points in the PLC.