OPC: Com-Server and automation technology

Visualization systems of various manufacturers have established themselves as standard solutions in the field of automation. They provide MMIs (man-machine interfaces). In order to remain independent of the many brand-specific protocols, most visualization systems use OPC (OLE for Process Control) technology for the transfer of data to and from the field level.

As shown in the diagram, the OPC server works as a gateway application. Towards the application, it provides a standardized OPC software interface, which makes I/O data available in the form of items. Towards the lower level, the values or contents of these items are detected by the OPC server by means of special protocols.

1 Windows application (visualization, SCADA, GLT, etc.).
Reads/writes I/O values (=items) from/to the OPC server

2 OPC server as software components from manufacturers of field devices, visualization systems or third-party suppliers. The OPC server provides OPC clients with I/O values in the form of items.

3 Ethernets are more and more replacing traditional RS232 and RS485 interfaces as the preferred transfer medium.

4 Any devices, such as PLCs, WebIO Digital, Web Thermometers, serial COM servers, etc.

 

What capabilities do W&T devices offer in OPC environments?

Integration of remote I/O points

Via the intranet, remote I/O points can be integrated into process visualization systems. As most companies already avail of complex network structures, there is virtually no limit as regards the distance between the visualization console and the I/O point. The costs for cabling are minimal.

Integration of remote serial messages

In addition to digital I/O points, the W&T OPC server also supports the communication with devices that are linked by serial connection to the Com-Server. The processing of ASCII alarms, cyclic measured values and messages or even a control system for a display panel as shown in the following diagram can be implemented based on the process visualization.

Integration of remote control systems by means of standard protocols

It is often necessary to integrate remote devices that use a standard serial protocol into visualization systems or other applications. Of course, it makes sense here as well to take advantage of the existing network infrastructure. The extent to which such serial protocols can be tunneled through the network depends largely on their timing specifications. Standard Ethernet meets only "soft" real-time requirements in this context.

In practice, integration is carried out via OPC, whereby either the product supplied by the hardware manufacturer or a third-party OPC server can be used. Depending on the capabilities of the OPC server, the physical connection is then established either directly via the socket interface (connection parameters = IP address + port number) or via the workaround of the W&T COM Port Redirector using a virtual COM port.