Open Platform Communications (OPC) is a series of standards and specifications for industrial

telecommunication Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...

. They are based on

Object Linking and Embedding Object Linking & Embedding (OLE) is a proprietary technology developed by Microsoft that allows embedding and linking to documents and other objects. For developers, it brought OLE Control Extension (OCX), a way to develop and use custom user i ...

(OLE) for process control. An

industrial automation Automation describes a wide range of technologies that reduce human intervention in processes, namely by predetermining decision criteria, subprocess relationships, and related actions, as well as embodying those predeterminations in machines ...

task force developed the original standard in 1996 under the name OLE for Process Control. OPC specifies the communication of

real-time Real-time or real time describes various operations in computing or other processes that must guarantee response times within a specified time (deadline), usually a relatively short time. A real-time process is generally one that happens in defined ...

plant data between control devices from different manufacturers. After the initial release in 1996, the

OPC Foundation The OPC Foundation (Open Platform Communications, formerly Object Linking and Embedding for Process Control) is an industry consortium that creates and maintains standards for open connectivity of industrial automation devices and systems, such as ...

was created to maintain the standards. Since OPC has been adopted beyond the field of process control, the OPC Foundation changed the name to Open Platform Communications in 2011. The change in name reflects the applications of OPC technology for applications in

building automation Building automation (BAS), also known as building management system (BMS) or building energy management system (BEMS), is the automatic centralized control of a building's HVAC (heating, ventilation and air conditioning), electrical, lighting, ...

discrete manufacturing Discrete manufacturing is the production of distinct items. Automobiles, furniture, toys, smartphones, and aeroplanes are examples of discrete manufacturing products. The resulting products are easily identifiable and differ greatly from process ...

, process control and others. OPC has also grown beyond its original OLE implementation to include other data transportation technologies including

Microsoft Corporation Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washingt ...

.NET Framework The .NET Framework (pronounced as "''dot net"'') is a proprietary software framework developed by Microsoft that runs primarily on Microsoft Windows. It was the predominant implementation of the Common Language Infrastructure (CLI) until bein ...

XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable ...

, and even the OPC Foundation's binary-encoded TCP format.

History

The OPC specification' was based on the OLE, COM, and DCOM technologies developed by

for the Microsoft Windows operating system family. The specification defined a standard set of

object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Object (abstract), an object which does not exist at any particular time or place ** Physical object, an identifiable collection of matter * Goal, an ...

s, interfaces e.g. IDL and

methods Method ( grc, μέθοδος, methodos) literally means a pursuit of knowledge, investigation, mode of prosecuting such inquiry, or system. In recent centuries it more often means a prescribed process for completing a task. It may refer to: *Scien ...

for use in process control and manufacturing automation applications to facilitate

interoperability Interoperability is a characteristic of a product or system to work with other products or systems. While the term was initially defined for information technology or systems engineering services to allow for information exchange, a broader defi ...

. The most common OPC specification is OPC Data Access, which is used for reading and writing real-time data. When vendors refer to "OPC" generically, they typically mean OPC Data Access (OPC DA). OPC DA itself has gone through three major revisions since its inception. Versions are backwards compatible, in that a version 3 OPC Server can still be accessed by a version 1 OPC Client, since the specifications add functionality, but still require the older version to be implemented as well. However, a client could be written that does not support the older functions since everything can be done using the newer ones, thus a DA-3-compatible client will not necessarily work with a DA 1.0 Server. In addition OPC DA specification, the OPC Foundation maintains the OPC Historical Data Access (HDA) specification. In contrast to the real time data that is accessible with OPC DA, OPC HDA allows access and retrieval of archived data. The OPC Alarms and Events specification is maintained by the OPC Foundation, and defines the exchange of alarm and event type message information, as well as variable states and state management. By 2002, the specification was compared to

Fieldbus Fieldbus is the name of a family of industrial computer networks used for real-time distributed control. Fieldbus profiles are standardized by the International Electrotechnical Commission (IEC) as IEC 61784/61158. A complex automated industrial ...

and other previous standards. An OPC Express Interface, known as OPC Xi, was approved in November, 2009, for the

. OPC Xi used

Windows Communication Foundation The Windows Communication Foundation (WCF), previously known as Indigo, is a free and open-source runtime and a set of APIs in the .NET Framework for building connected, service-oriented applications. .NET Core 1.0, released 2016, did not sup ...

instead of DCOM, so it can be configured for communication across the enhanced security of network address translation (NAT). About the same time, the OPC Unified Architecture (UA) was developed for platform independence. UA can be implemented with

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...

Microsoft .NET The Microsoft .NET strategy is a marketing plan that Microsoft followed in the early 2000s. Steve Ballmer described it as the company's "most ambitious undertaking since Internet Strategy Day in 1995". In support of this strategy, between 2000 and ...

, or C, eliminating the need to use a Microsoft Windows platform of earlier OPC versions. UA combined the functionality of the existing OPC interfaces with new technologies such as

and Web services to deliver higher level

manufacturing execution system Manufacturing execution systems (MES) are computerized systems used in manufacturing to track and document the transformation of raw materials to finished goods. MES provides information that helps manufacturing decision-makers understand how curr ...

(MES) and

enterprise resource planning Enterprise resource planning (ERP) is the integrated management of main business processes, often in real time and mediated by software and technology. ERP is usually referred to as a category of business management software—typically a sui ...

(ERP) support. The first working group for UA met in 2003, version 1.0 was published in 2006. On September 16, 2010, The OPC Foundation and the

MTConnect MTConnect is a manufacturing technical standard to retrieve process information from numerically controlled machine tools. As explained by a member of the team that developed it, "This standard specifies the open-source, royalty-free communicatio ...

Institute announced cooperation to ensure interoperability and consistency between the two standards.

Design

OPC was designed to provide a common bridge for Windows-based software applications and process control hardware. Standards define consistent methods of accessing field data from plant floor devices. This method remains the same regardless of the type and source of data. An OPC Server for one hardware device provides the same methods for an OPC client to access its data as any other OPC Server for any hardware device. The aim was to reduce the amount of duplicated effort required from hardware manufacturers and their software partners, and from the supervisory control and data acquisition (SCADA) and other

human-machine interface In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine fr ...

(HMI) producers in order to interface the two. Once a hardware manufacturer had developed their OPC Server for the new hardware device, their work was done with regards to allowing any 'top end' to access their device, and once the SCADA producer had developed their OPC client, it allowed access to any hardware with an OPC compliant server. OPC servers provide a method for different software packages (as long as it is an OPC client) to access data from a process control device, such as a programmable logic controller (PLC) or

distributed control system A distributed control system (DCS) is a computerised control system for a process or plant usually with many control loops, in which autonomous controllers are distributed throughout the system, but there is no central operator supervisory contro ...

. Traditionally, any time a package needed access to data from a device, a custom interface or driver had to be written. There is nothing in the OPC specifications to restrict the server to providing access to a process control device. OPC Servers can be written for anything from getting the internal temperature of a microprocessor to the current temperature in Monument Valley. 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 can be linked and communicate to other servers. 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. Some OPC specifications are published, but others are available only to members of the OPC Foundation. So while no company "owns" OPC and anyone can develop an OPC server whether or not they are a member of the

, non-members will not necessarily be using the latest specifications. It is up to each company that requires OPC products to ensure that their products are certified and that their system integrators have the necessary training.

References

External links

FatRat Library - free OPC server developers toolkit

OpenOPC - Open Source OPC client development in Python

OPC Foundation

OPC Programmers' Connection

OPC Unified Architecture Address Space e-book

prOpc Library - Open Source OPC server/client toolkit in Delphi
{{Automation protocols Application programming interfaces Industrial automation Computer standards

History

Design

See also

References

External links