The development of software drivers to connect industrial software packages to I/O systems historically has been a resource drain for both developers and users. The proliferation of both hardware and software options as well as the inconsistencies and incompatibilities among different software drivers, made the task of interfacing hardware, such as an I/O system, to a wide range of software options very complex.
In response to these issues, a number of leading automation hardware and software suppliers, working in conjunction with Microsoft, collaborated on defining a new communications standard based on Microsoft’s Object Linking and Embedding (OLE) – that is now referred to as Active X technology.
This new standard OLE for Process Control (OPC) promises to allow plug and play hardware and software components from different suppliers that users can easily integrate into corporate-wide automation systems.
OPC itself is a standardised interface for device servers, which may be connected to I/O devices, PLCs, Fieldbus and so on, to communicate with process control software systems, such as MMI/SCADA systems. Because the interface is a standard, users can be confident that a single OPC server, such as the National Instruments’ FieldPoint OPC Server, will work easily with any software that implements an OPC interface.
Based on OLE, Component Object Model (COM) and Distributed COM (DCOM) technologies, OPC defines a set of standard objects, properties and methods for process control and automation applications. The specification also defines a standard mechanism to access named data items contained in the device servers. An OPC server provides an interface to OPC Objects, allowing client applications to control devices and manage device data in a generic fashion. OPC-compliant software can therefore communicate with any OPC server, independent of the particular hardware device or I/O handled by the server.
DCOM enables an additional level of functionality for OPC, allowing a client application to use objects located on other networked computers. Therefore, an MMI or SCADA software package can execute and collect data from OPC servers that are running on any computers on the network.
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