Open Platform Communications (OPC)

History of OPC

In 1995, four industrial automation vendors started a task force to standardize the data-access protocols of their devices, which were then predominantly running Microsoft operating systems.

The goal was to abstract the communication protocols of programmable logical controllers (PLCs), small, special-purpose computers that are widely used in industrial automation. Abstracting these different protocols allowed a standardized interface that served as a sort of middleman converting read/write requests between the human-machine interface (HMI) software that workers use to control machines via PLCs, and SCADA (supervisory control and data acquisition), a popular computer architecture for industrial process control.

In 1996, the task force released version 1.0 of the standard, called OPC -- later renamed OPC Classic -- which other hardware and software vendors began to adopt. The OPC Foundation was started the same year to formalize compliance, certification, interoperability and validation procedures.

OPC Classic specifications

The first version of the OPC standard was based on a Microsoft technology for exchanging data between software components, called DCOM (Distributed Component Object Model), a subset of COM (Component Object Model). The original meaning of OPC was OLE for Process Control, which refers to OLE (Object Linking and Embedding), a Microsoft COM desktop technology for embedding and linking documents and other software objects.

In 1998, the OPC Foundation began to convert the original specification to web services.

There are three OPC Classic specifications:

• OPC Data Access (OPC DA) defines OPC client-server technology and how software can read and write data, as well as the data types and structures available.
• OPC Alarms and Events (OPC AE) describes the ways OPC server software can monitor systems and send alarms to client software.
• OPC Historical Data Access (HDA) defines the queries and analytics that can be applied to the historical time-stamped data collected from devices.

OPC Unified Architecture

In 2008, after Microsoft deemphasized DCOM, and to make it easier for vendors of OPC software to expand to non-Windows devices, the OPC Foundation released the current standard, OPC Unified Architecture (OPC UA). It is backward compatible with OPC Classic and based on service-oriented architecture (SOA), a software-design approach that has become more widely used in manufacturing systems.

OPC UA is an extensible SOA framework designed to support a wide range of platforms, from embedded microcontrollers to cloud infrastructure. It provides security through encryption, authentication and auditing. It goes beyond OPC Classic by adding on-demand capabilities, the ability to discover servers and other systems on a network, and an address-space scheme meant to allow more complex data structures.

The OPC Foundation provides downloadable COM proxy wrappers for integrating OPC UA and OPC Classic products.

As of late 2017, the OPC Foundation claimed 470 member companies around the world. Leaders in the software, hardware, industrial automation, machine-to-machine (M2M), smart energy and discrete- and process-manufacturing sectors are members. Among the well-known brands are Honeywell, IBM, Microsoft, Pfizer, Rockwell, Samsung, SAP and Siemens.

In recent years, vendors of Industrial Internet of Things (IIoT) technology have used OPC UA in product demonstrations, and in 2016 the OPC Foundation announced a partnership with the Object Management Group and its program, the Industrial Internet Consortium, to integrate the two standards for IIoT.