Tapping into Control Data via Ethernet and the Internet

EP Editorial Staff | October 1, 2003

OPC Foundation is removing barriers between traditionally proprietary factory floor devices, systems, and other manufacturing software.

One of the most notable trends in manufacturing today is the desire to integrate real-time operating and equipment status data from field devices and measurement and control systems with enterprise-wide systems controlling overall plant production and asset management. End-users want a seamless exchange of production and equipment status information across the plant floor with production management and business systems to facilitate faster decisions, increased productivity, and better management of plant and corporate assets.

One of the biggest barriers to achieving this goal is the inability to easily integrate information from plant-floor measurement and control systems with production and maintenance management systems. It is difficult, if not impossible, to share data between systems without industry standards to facilitate interoperability.

Custom drivers and interfaces can be written, but this process is usually quite complex due to the multitude of different measurement and control devices and software packages that exist in a typical plant.

Standards promote interoperability
There is a great deal of momentum in the plant automation and condition monitoring industries to provide integrated solutions based on open industry standards that leverage off-the-shelf, commercial computer hardware and software technology such as Ethernet networks, XML (eXtensible Markup Language), and the Internet to provide access to information.

OPC has emerged as the worldwide industry standard, enabling connectivity and interoperability of plant-floor information between disparate fieldbus networks, programmable controllers, distributed control systems, condition monitoring, plant asset management, and production management systems. The OPC industry standard delivers the same connectivity and interoperability benefits to plant measurement, automation, and condition monitoring systems that standard printer drivers brought to word processing.

The OPC Foundation (www.opcfoundation.org) is an independent, nonprofit, industry trade association comprised of more than 300 automation suppliers worldwide. In the nearly 8 years since the formation of the foundation and release 1.0 of the Data Access specification in 1996, the movement to adopt OPC as the industry standard for sharing information among disparate industrial control devices and factory automation systems has gathered momentum and acceptance with automation users, suppliers, and system integrators.

OPC has evolved from the original Data Access (OPC DA) standard capable of bridging the gap across plant floor measurement, control, and condition monitoring systems to new OPC standards such as OPC XML-DA that leverage the Internet and XML to encompass vertical information integration with enterprise systems.

OPC’s evolution parallels Ethernet’s move to flatten plant floor networking hierarchies. As Ethernet becomes the standard for plant floor and enterprise connectivity, OPC provides a unified approach to interconnecting software solutions horizontally and vertically throughout the enterprise.

What is OPC Data Access?
OPC DA—based on component object model (COM) and distributed COM (DCOM), key technologies in Microsoft’s .NET for Manufacturing integration framework—defines an industry-standard application programming interface (API). The OPC DA specification defines a set of standard COM objects, methods, and properties that specifically address interoperability requirements for factory automation, process control, and machine condition monitoring applications. OPC DA leverages DCOM, allowing client/ server applications to access plant-floor data via an Ethernet network distributed across the manufacturing enterprise.

Many suppliers ship products with built-in OPC support. Software developers use the OPC DA specification to implement OPC server and client capability into their products, thus providing plug-and-play connectivity and interoperability between a variety of measurement and control devices, systems, and industrial networks both on the factory floor and across the manufacturing enterprise.

Any product with an OPC server built-in provides a standard interface to the OPC DA COM objects, allowing any OPC client application to exchange data in a common format. The OPC DA interface provides an abstraction layer, so the OPC client cannot tell if data is coming from a PLC, DCS, or a data acquisition system monitoring machine vibration (Fig. 1).

What is OPC XML-DA?
Two years ago, the OPC Foundation formed the OPC XML-DA technical working group to define a new specification to move the same type of plant floor data as the existing OPC DA COM-based specification, but leverage Internet technology as the primary mechanism to guarantee interoperability between applications.

OPC XML-DA provides vertical integration between the plant floor and condition monitoring, maintenance, production management, and enterprise applications using XML, HTTP, and SOAP industry standards. OPC DA based on COM/DCOM is primarily used to provide horizontal data integration and interoperability between measurement and automation systems on the manufacturing floor and plant applications performing monitoring, alarming, historical data collection, and supervisory control.

The OPC Foundation selected XML as an alternative to the existing OPC DA COM-based specification for moving plant floor data because it provided several benefits:

  • XML, HTTP, SOAP, and other Internet standards referenced in the OPC XML-DA specification are vendor neutral and supported on multiple computer platforms, unlike COM/ DCOM that was primarily designed for a Microsoft Windows-centric environment. Existing OPC DA COM-based applications work well for plant floor systems connected to a typical Ethernet LAN, but DCOM was not designed to be used to pass data through a firewall.
  • XML is an open standard that provides data integration and interoperability using the Internet. This was an important factor as the Internet becomes more prominent for information exchange between the plant floor and other applications distributed across the manufacturing enterprise. XML was specifically defined by the World Wide Web Consortium (W3C) to be compatible with existing Internet communication protocols such as HTTP. XML is the preferred format for encoding and moving structured data in an open, system-independent way.
  • XML leverages powerful Web application development tools enabling faster application development. XML and the Internet technology also provide new and powerful ways of accessing and delivering plant floor, condition monitoring, e-diagnostic, and asset management information to users across the manufacturing enterprise using standard Web browsers and wireless devices such as personal digital assistants (PDAs) and cell phones in formats that the user can easily define and customize.

OPC XML-DA provides better connectivity and interoperability for production management and enterprise applications such as manufacturing execution systems (MES), enterprise resource planning (ERP) systems, computerized maintenance management systems (CMMS), enterprise asset management (EAM) systems, and plant optimization that need to access plant-floor data. Many times these types of applications are running on non-Microsoft computer platforms that do not have built-in support for the COM interfaces used with OPC DA.

The OPC XML-DA is complementary with products based on the existing OPC DA specification (Fig. 2). OPC XML-DA was specifically designed to allow existing OPC DA COM-based products to be “wrapped” by the new OPC XML-DA interface and in effect support both interfaces from the same OPC server.

Any supplier can develop a generic OPC XML-DA wrapper to “Internet enable” existing OPC DA servers allowing them to publish plant floor data to the Web. This was an important consideration to get new OPC XML-DA products to market by leveraging the more than 500 OPC DA products that exist today.

Using OPC for maintenance and reliability applications
Timely and accurate plant floor and equipment status information is critical for assessing and optimizing equipment utilization, reliability, and uptime. It is also important for developing proactive maintenance and asset management programs. OPC provides open, industry-standard access to plant floor, equipment health, and e-diagnostic data when someone needs it, giving plant operations and maintenance personnel the capability to make better management decisions.

CMMS and e-diagnostic applications can use OPC to monitor real time and historical operating parameters such as machine vibration, oil analysis, pressure and temperature data, uptime, and operating status of equipment on the plant floor. Access to this information helps to assess health, identify faults, and schedule preventive maintenance.

Maintenance management, CMMS, and EAM applications working together with PLC, DCS, and data acquisition systems monitoring and controlling the plant provide plant operators and maintenance personnel with a much better view of equipment health, allowing them to take corrective action to eliminate a fault before it affects products or causes unscheduled downtime.

Machine health and predictive maintenance is critical to every reliability program. Many vendors have OPC connectivity built into their hardware and software products. These products are used to implement reliable, robust, and flexible condition monitoring solutions that leverage industry standards including OPC and the Internet. Figure 3 shows an example of how OPC is used for machine condition monitoring.

The OPC Foundation is working with the Machinery Information Management Open Systems Alliance (MIMOSA), a trade association for the MRO solutions industry that develops and promotes information integration specifications to enable open industry-driven integrated solutions for managing complex high value assets. Last year, the foundation and MIMOSA started work on a joint initiative to produce Consensus-Based Industrial Standards for Maintenance, Repair and Operating (MRO) Information.

Initial efforts focus on leveraging existing XML-based specifications developed by OPC and MIMOSA, respectively. The OPC Foundation and MIMOSA believe this is an important opportunity to establish a coordinated family of industry-accepted information standards as the preferred alternative to multiple independent and potentially incompatible standards. Collaboration between MIMOSA and the OPC Foundation will extend the reach of both standards, allowing MRO applications to have open, industry-standard access to condition monitoring, diagnostic, and asset management information from monitoring and control systems.

The OPC Foundation Complex Data technical working group is making enhancements to the OPC DA specification based on requirements identified by MIMOSA and feedback from other industry groups to address additional types of data such as structures, arrays, and binary. The OPC Complex Data initiative will provide a way for OPC client applications to read and decode new data types from OPC servers.

The current OPC DA 3.0 specification primarily deals with scalar data that represents 90 percent of typical plant floor data. Scalar data might represent machine operating parameters from analog measurements such as pressure, temperature, flow, level, and vibration, or discrete signals used to represent on/off state or abnormal alarm conditions.

Many predictive maintenance and CMMS applications need to access more information such as oil analysis, vibration waveforms, power spectrums, or thermal images generated by infrared thermography in addition to typical operating parameters. Current OPC DA clients might be able to read vibration waveform data from an OPC sever, but would likely have problems interpreting and using the data.

OPC complex data will extend the OPC DA specification to allow OPC client applications to read and decode any type of data capable of being generated by measurement and control systems on the plant floor. OPC is also used to publish results from machine condition monitoring and predictive maintenance applications back to PLC and DCS control systems—providing real-time predictive maintenance information for advanced control and optimization—or to send results to display screens used by operators monitoring the manufacturing process on the plant floor.

The benefits of OPC
OPC creates an industry-standard framework to deliver plug-and-play components from a wide variety of automation suppliers that can easily integrate into corporate-wide automation and business systems, something that has been virtually unachievable in the past.

OPC technology extends beyond industrial data acquisition hardware I/O to more complex control and business systems. HMI, DCS, SCADA, modeling, simulation, advanced control, CMMS, EAM, scheduling, and other applications can act as OPC clients and servers to permit data exchange between cooperating applications—permitting the user to focus more on value-added business activities versus system integration problems. Users realize reduced integration costs because OPC components from different automation suppliers adhere to a single, industry-standard interface.

Any application software that supports the OPC client interface can exchange information with any device, control system, or industrial network that provides an OPC server interface. The end-user benefit is that OPC removes barriers between traditionally proprietary factory floor devices, systems, and other manufacturing software. This provides increased flexibility and reduced integration, development, and installation costs of factory automation, process control, and production management systems.

Delivering tomorrow’s technologies
By adopting products based on industry-standard interfaces defined by the OPC specification, manufacturers and automation suppliers both benefit by realizing seamless integration of plant floor information into production, maintenance, and asset management systems and decreased integration costs. OPC interoperability standards for the manufacturing industry give users the freedom to choose best-of-class solutions without the fear that they will not work together and the opportunity to enjoy lower total cost of ownership. MT

Don W. Holley is the industrial automation marketing manager at National Instruments Corp., 11500 N. Mopac Expwy., Bldg. B, Austin, TX 78759; telephone (512) 683-0100


.NET: Microsoft software technologies that enables a high level of software integration using Web services.

API: application programming interface

COM: component object modeling

DA: data access

DCOM: distributed component object modeling

Ethernet: A network standard of communication

HTTP: hypertext transfer protocol

OLE: object linking and embedding

OPC DA: OPC data access

OPC XML-DA: OPC web services specifications

SOAP: simple object access protocol

TCP/IP: transmission control protocol/internet protocol

XML: extensible markup language



Fig. 1. OPC provides industry-standard interoperability between enterprise information and control systems. The OPC client cannot differentiate between sources of data.

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Fig. 2. OPC DA and OPC XML-DA provide plant floor to manufacturing enterprise integration on Microsoft and non-Microsoft systems.

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Fig. 3. OPC provides the glue for a machine condition monitoring application.

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