Access 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 Gateway Communication Driver means.

To access an OPC item, the OPC client needs to connect to Gateway Communication Driver (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, Gateway Communication Driver 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 Gateway Communication Driver.

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 Gateway Communication Driver, the program name is OI.Gateway.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 Gateway Communication Driver under a specific data source for the common custom attributes between Gateway Communication Driver and the source, such as update interval. If not specified from the client, the default device group using the global configuration attribute values from Gateway Communication Driver 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 Gateway Communication Driver under the OI Server Manager, separated by delimiters.

• item name: A specific data element, the leaf of the hierarchy tree of Gateway Communication Driver, 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 Gateway Communication Driver. For more information, see Connect to an OPC data source.