OPC - OLE For Process Control Paul C. Shafer Bently Nevada Corp.

What OPC is NOT OPC in and of itself is not an Object Technology It’s not an OO Database Not a database... So… what’s this guy doing?

What is OPC A “real world” application of object technology used to devise a standard communication system to enable industrial plant floor devices and business software applications to communicate via a standard common protocol.

What is OPC (continued) Industrial communication standard –Base on Microsoft’s OLE and COM technologies –Managed by OPC Foundation ( –provides a common interface for communicating with diverse process-control devices

Communication Communication and integration of plant information systems: –Many different plant floor devices and process control software applications from many different vendors –Business Information and Management software

Information Islands Business Management Process Management Plant Floor and Automation Devices

Legacy Solutions Companies had to independently develop “drivers” to access data. –Duplication of effort –Inconsistencies between drivers –Support for hardware feature changes –Access conflicts

A Better Way: OPC The OPC Standard now places the burden on hardware vendors to develop a single OPC “driver” (server) that is responsible for data collection and distribution for their device(s). Provide data to clients in a standard manor.

Client / Server Relationship Software developers can now write clients that can communicate with hardware OPC servers using a common, efficient protocol

Technology (TLA Guide) COM - Component Object Model –Provides objects as reusable, binary components –objects “expose” a set of interfaces that client applications can use to access the object’s services. –Implementation is encapsulated behind interfaces (allows object to change without requiring client recompilation)

Technology (continued) COM (continued) –Dynamic interrogation of objects (IUnknown::QueryInterface) –Overcomes many of the problems with OO programming by itself, class libraries and Dynamic Link Libraries (DLL). –True “off-the-shelf” components that can be plugged in to your application

Technology (continued) DCOM - Distributed Component Object Model –remote objects appear to be local OLE - Object Linking and Embedding –based on COM (e.g. an OLE object implements certain COM interfaces) –provides integration among applications

Technology (continued) OLE Automation –Allows components to easily be used by high level custom programs (e.g. written in VB or VBA) –Set of special COM interfaces automation or ActiveX objects implement these “automation” interfaces –Automation Controllers Clients that can integrate those objects

Technology (continued) ActiveX –Umbrella term that used to be known as OLE controls. Now “ActiveX” controls. COM / ActiveX technology is really what allows the “plug-in” reusable components.

OPC and COM OPC Specifications contain defined COM interfaces Server and Client Interfaces –Data Access –Historical Data –Alarms and Events –etc. Implementation and development

OPC Interfaces Custom Interfaces –COM interfaces –Required by all OPC servers –Clients written in C++ will typically use the custom interface more efficient than Automation interface greater flexibility and power (e.g. Automation interfaces limit you to “automation compatible” types as parameters and return values)

Interfaces Automation Interfaces –OLE Automation –Optional implementation –Suited for scripting language clients (e.g. VBA) or automation controllers.

Conclusion No longer information Islands –OPC Servers and Clients allow devices, control software and business information and management software applications to communicate via an industry accepted standard protocol.

Conclusion Business Management Process Management Plant Floor and Automation Devices

References OPC TaskForce, OLE for Process Control Standard, Final-Release Version 1.0, OPC Foundation home page: Box, Don. Essential COM Addison Wesley Longman Inc Robinson, Steve, Krassel, Alex “COMponents”, Panther Software Brockschmidt, Kraig. Inside OLE, Second Edition. Microsoft Press, Redmond, WA, Mark Edmond, Efforts Advance to Tie Shop-Floor Automation to Back-Office Systems, Start Magazine Volume 2, Number 1, January / February OPC TaskForce, Definitions and Interfaces, Version 1.0, 1998 “OPC Finds Strong Validation Among End Users”, No Rest for the Dedicated, Control Magazine, September