01 June 2002
OPC spreads wings
By Jim Strothman
Two next-gen OPC specs near touchdown, but this gen still flies high
Even as cross-industry software experts develop two next-generation OLE for process control (OPC) standards specifications, this generation's OPC technology continues to break new manufacturing industry ground.
Managed by the OPC Foundation, the existing OPC specification defines a set of standard interfaces based on Microsoft's 7-year-old object linking and embedding/component object model (OLE/COM) technology. The standard allows totally different automation and control applications, systems, and devices-supplied by different vendors-to work and exchange data with one another.
Before a simple "stage 1" OPC specification debuted in 1996, every software application developer needed to write a custom interface, or driver, to exchange data with hardware field devices. OPC eliminated that headache by defining a common interface that could be written once, than easily reused by human-machine interface (HMI), supervisory control and data acquisition (SCADA), and other control systems and applications.
This-generation OPC's COM-based technology was fine in 1996, when security was less of a concern. The problem today is COM technology uses binary data that firewalls often block.
OPC XML, DX en route
At National Manufacturing Week in March, the OPC Foundation previewed its next-generation but still evolving OPC XML specification. The extensible markup language (XML) protocol and Microsoft's .NET (dot-net) architecture are the basis of OPC XML.
XML uses ASCII code, which is "firewall friendly" and doesn't get blocked. There's one disadvantage, however: XML technology is generally slower than COM.
Insiders developing the OPC XML specification say it is close to completion, while yet another OPC version-OPC data exchange (OPC DX)-probably won't be ready until near the end of this year.
Previewed in April at Hannover Fair 2002, OPC DX would do away with "bridges" needed to exchange data among different bus protocols-for example, those of the Open DeviceNet Vendor Association, Profibus, the Fieldbus Foundation, and ControlNet International.
Huge paper plant installation
While next-generation development proceeds, today's COM-based OPC technology rolls on, gaining steam and breaking ground in installation sizes and first-ever manufacturing applications.
In what Iconics founder and president Russ Agrusa calls "the ultimate OPC application," giant Austria-based pulp and paper producer The Frantschach Co. installed what's believed to be the largest Web-based HMI application in Eastern Europe. Agrusa said plant management told him efficiency went up 70% since installation began two years ago.
A Frantschach Pulp & Paper division state-of-the-art plant in Steti, Czech Republic, makes kraft paper like that used for paper bags in supermarkets. The plant employs up to 3,000 workers in 125 buildings. Daily, it can process 1,000 tons of lumber and produce about 1,500 tons of paper.
Plant management wanted to integrate nine different OPC servers, including Measurex, SAP, GE, OSI PI, Modbus, Siemens, and others, into one application. "The plant manager's vision," Agrusa said, "was to walk up to any of 150 computers in the plant and, using [Microsoft's] Internet Explorer as the browser, look at the nine control systems as one integrated, Web-based application." Now operating, the system can change set points (control), as well as monitor operations, Agrusa said.
OPC standards based
The Merz Co. acted as consultant and systems integrator for Frantschach's HMI/SCADA system, called the technological information system (TIS). Using Iconics' Genesis32 and WebHMI software, TIS comes from industry-standard OPC data access, historical data access, and alarm and events communications. It uses 20 full Genesis32 systems with more than 100 graphics screens for real-time HMI visualization of the plant's operations.
Up to 50 HMI clients can view production, maintenance, and management data simultaneously using Web browsers on PCs throughout the facility. The TIS uses Iconics' DataWorX32 data-collection engine for more than 4,500 real-time OPC tags and more than 10,000 sensors tracking historical OPC tags. By comparison, nuclear power plants use about 5,000 tag-tracking sensors.
"Iconics' WebHMI software, SAP, OSI PI, and our integrator, Merz, have created the most powerful Web-enabled technological information systems for monitoring and analyzing our complete pulp and paper plant application," said Lubomir Rulisek, the plant's pulp mill manager.
"This is what OPC is all about: connecting all those disparate systems with a common software interface," Agrusa said.
Pro-Tec Coating Co., a Columbus, Ohio-based joint venture of U.S. Steel and Kobe Steel, also installed a cutting-edge-albeit much smaller-OPC application.
Pro-Tec has two continuous hot-dip galvanizing lines in its Leipsic, Ohio, plant, with a combined production capacity of 1 million tons per year.
It handles steel coils up to 90,000 pounds, 24 to 84 inches wide, and up to 18,000 feet long to produce premium-grade products used in automotive, appliance, and electronic packaging applications.
The control system for line 2 started during the first quarter of this year. Pro-Tec is about to install the systems for line 1 and will be operational within the next month, said Robert G. Wilhelm, owner of Objective Control Ltd. in Powell, Ohio.
Wilhelm and Dick Corson, owner of Corson Manufacturing Consulting in Columbus, Ohio, teamed to install Pro-Tec's fourth-generation, model-based coating weight control system. The system collects process data from the line, "air knives" (actually, carefully controlled air jets that blow air at the steel strip to wipe off excess zinc), measurement system, and annealing furnace. It outputs set points to the air knife pressure and distance controllers, carriage positioning system, knife height system, and correcting roll.
The coating weight control system resides in a control PC. It obtains process I/O from several programmable logic controllers (PLCs) using OPC. They use other PCs as remote HMI terminals and also obtain data using OPC.
Wilhelm, who holds several patents in sheet measurement and control, said a program called GalvControl is the real-time control application that controls coating weight on the galvanizing line. It obtains all its process I/O and performs most of its HMI communications using OPC. Iconics' DataWorX acts as a central OPC client/server bridge between the HMI client and control client, making it possible to transparently support redundant process I/O from multiple PLCs, Wilhelm said.
GraphServer, a thin-client application, adds more complex graphics capability (three-dimensional plots and distance-based rather than time-based trending) to the HMI. Wilhelm said the control application uses Matlab's math library to support its complex mathematical modeling requirements. WBJ
This, the most important of many operator screens in Pro-Tec's coating process, shows measured coating along the strip, both top and bottom sides, downstream from the scanning X-ray coating weight gauge. Also shown is the coating weight between the air knives and measuring gauge, as predicted by the model (dotted lines on trend). "Profiles" shows the distribution of coating across the strip for both top and bottom sides. Major control parameters and plots overlay on a schematic of the coating section of the line.