Integrate OPC with non-Windows

InTech, Oct 2001 by Sheble, Nicholas

Houston-Mark Janke is a field application engineer at InTrinsyc Software. He contributed the following thoughts and networking updates during ISA's conference and exhibition last month.

"With the growing need to connect business-centric enterprise systems with control systems, there are many hurdles to overcome and many technologies and technical approaches from which to choose.

"Check out these practical methods for getting data from the factory floor to enterprise systems, where one can use it to reduce facility operation costs.

INTERFACE TO LEGACY RIG

"Acquisition of data from legacy systems can be difficult. Until recently, no standards existed to describe an interface with control system hardware. At the device level, connectivity is equally proprietary. To address this, several industrial automation vendors have collectively developed the OPC [OLE for process control] specification.

"This specification describes the standardization of a COM [component object model] object. COM technology is paramount because of the dominance of the Windows operating systems within control system solutions.

"Utilizing COM and DCOM [distributed COM] to support a common interface across a network, gateways have emerged. Using these gateways, Windows-centric enterprise systems supporting DCOM communications can acquire data from OPC server objects on the plant floor.

"This provides a smooth flow of data from devices on a proprietary network into the enterprise. As network communication technology moves beyond DCOM and into SOAP [simple object access protocol] described by XML [extensible markup language], so too does the OPC specification.

"An OPC standard that describes how SOAP/XML handles data transfer is nearing completion. Gateway technology that exposes data via SOAP/ XML is under development from a variety of industrial automation vendors and may soon be available.

"A benefit to using SOAP/XML for OPC is that non-Windows-based enterprise platforms will be able to access OPC data from Windows-based control system gateways. Such connectivity is feasible because SOAP/XML for OPC is, in effect, simple textual information over HTTP [hypertext transfer protocol]. Virtually every system in production today has the ability to pass text over HTTP.

GATEWAY TO THE PATHWAY

"Control system hardware may utilize proprietary, or reasonably proprietary, technologies for device communications but typically also includes the capability to communicate using OPC for interconnection with other software or systems. System hardware that remains wired to device networks while supporting OPC may include:

Application nodes designed to support third-party software add-ons.

Engineering nodes designed to support system development and administration facilities.

Human-machine interface nodes designed to provide operations with a view of system run-time data in a graphical format.

Gateway nodes designed for the sole purpose of transferring data between systems.

"Data transfer is a secondary function of these first three nodes.This may be problematic when communication between the plant floor and the enterprise is important.

"OPC/COM communication requires DCOM to facilitate connectivity over a LAN. Note that while DCOM is available out of the box with Windows operating systems, alternative technologies are available that provide more robust DCOM communications. Such third-- party solutions are worth considering when the enterprise-to-factory-floor link is vital.

WHAT ABOUT THE JAVA APPS?

"While the OPC/COM approach can prove very effective for connecting Windows-centric control system platforms and Windows-centric enterprise platforms, it may prove ineffective as a method for communication with enterprise platforms running Java applications.

"Control system platforms are mostly Windows based. Java applications on enterprise systems are equally predominant. Considering that Java applications do not natively communicate with COM-based technology such as the currently available OPC solutions, how can data transfer between these platforms?

"Fortunately, there are Java/COM bridging technologies available to cross this gap. Using a Java/COM bridge, Java applications running on enterprise platforms can communicate with OPC applications on Windowsbased control system platforms. On some rare occasions, a Java-centric control system platform may have to communicate with a Windows-based enterprise system.

"Because available Java/COM bridging technology is bidirectional, it can handle this scenario. A Java/COM bridge can deploy to bridge enterprise and control systems effectively, regardless of platform types."

InTech senior technical editor Nicholas Sheble edits Fieldbus News. Contact him at nsheble@isa.org.