OLE for process control

OLE for Process Control (OPC) which stands for Object Linking and Embedding (OLE) for Process Control, is the original name for a standards specification developed in 1996 by an industrial automation industry task force. The standard specifies the communication of real-time plant data between control devices from different manufacturers.

After the initial release, the OPC Foundation was created to maintain the standard. Since then, standards have been added and names have been changed. As of June, 2006, "OPC is a series of standards specifications". (Seven current standards and two emerging standards.) "The first standard (originally called simply the OPC Specification"), is "now called the Data Access Specification", or (later on the same page) "OPC Data Access", or OPC Data Access Specification.

While OPC originally stood for "OLE for Process Control", the official stance of the OPC Foundation is that OPC is no longer an acronym and the technology is simply known as "OPC". One of the reasons behind this is while OPC is heavily used within the process industries, it can be, and is, widely used in discrete manufacturing as well. Hence, OPC is known for more than just its applications within process control.

Origin and uses

The OPC Specification was based on the OLE, COM, and DCOM technologies developed by Microsoft for the Microsoft Windows operating system family. The specification defined a standard set of objects, interfaces and methods for use in process control and manufacturing automation applications to facilitate interoperability.

OPC was designed to bridge Windows based applications and process control hardware and software applications. Standard defines consistent method of accessing field data from plant floor devices. This method remains the same regardless of the type and source of data.

OPC servers provide a method for many different software packages to access data from a process control device, such as a PLC or DCS. Traditionally, any time a package needed access to data from a device, a custom interface, or driver, had to be written. The purpose of OPC is to define a common interface that is written once and then reused by any business, SCADA, HMI, or custom software packages.

Once an OPC server is written for a particular device, it can be reused by any application that is able to act as an OPC client. OPC servers use Microsoft’s OLE technology (also known as the Component Object Model, or COM) to communicate with clients. COM technology permits a standard for real-time information exchange between software applications and process hardware to be defined.

Future

The OPC Unified Architecture (UA) has been specified and is being tested and implemented through its Early Adopters program. It can be implemented with Java, Microsoft .NET, or C, eliminating the need to use a Microsoft Windows based platform of earlier OPC versions. UA combines the functionality of the existing OPC interfaces with new technologies such as XML and Web Services to deliver higher level MES and ERP support. It looks to become the standard for exchanging industrial data, replacing FactoryTalk, Archestra, some Modbus applications, and OPCDA.