Accessing Data Using OPC

In the case of OPC communications, the protocol addresses an element of data in a conversation with six characteristics: node name, program name, group name, device group, link name, and item name.

• The node name (required for remote access) and device group are optional.

• A fully qualified OPC Item name (ItemID) is composed of the link name and item name.

• All other characteristics are specified through separate OI Gateway means.

To access an OPC item, the OPC client needs to connect to OI Gateway (only out-of-process) and create an OPC group defining the data-acquisition properties for the collection of items to be added. Although OPC groups can be either public or private, OI Gateway only supports private groups. Public OPC groups are shared across multiple clients, whereas private OPC groups are local to a single client. Optionally, a device group, which indicates the access path to the items for read/write, can be specified from OI Gateway.

The following briefly describes each characteristic of OPC data access:

• node name: Computer (host) name identifying a specific node on the network (for Remote Access only).

• program name: The registered OPC server name uniquely identifying a specific server (ProgID). For OI Gateway, the program name is ArchestrA.FSGateway.3.

• group name: The OPC group created from the client for organizing a collection of items logically with the same data acquisition properties between the client and the server, such as update rate.

• device group: Meaningful names configured in OI Gateway under a specific data source for the common custom attributes between OI Gateway and the source, such as update interval. If not specified from the client, the default device group using the global configuration attribute values from OI Gateway is assumed. Functionally, a device group is equivalent to an access path (optional).

• link name: The set of hierarchy node names, representing the specific data source on a communications path link from the hierarchy root to a specific source as configured for OI Gateway under the OI Server Manager, separated by delimiters.

• item name: A specific data element, the leaf of the hierarchy tree of OI Gateway, within the specified group.

• item suffix: Optionally configure OPC data sources to use the /VT item suffix to tell the underlying OPC server the type of data you want the underlying OPC server to report to OI Gateway. For more information, see Connecting to an OPC Data Source.