What is OPC?
OPC (OLE for Process Control) is a communication standard based on OLE / COM technology. This is a special means of data exchange between MS-Windows applications. The OPC Foundation, which was created on the initiative of the main operators of the automation industry, publishes and maintains specifications that more specifically satisfy the industrial requirements of this sector.
Why to use OPC?
The purpose of the standard is to provide a common means for data access applications from any source, from field devices or from other files or applications.
The great motivation to create the OPC ™ OLE for the Process Control standard is the need to establish a standard mechanism for communication between different data sources, either from field devices or even from other data files.
Information architecture in an Industrial Manufacturing Process involves three levels:
Field Management: with the advent of intelligent field equipment, a wide variety of data equipment, such as configuration and control data, may be users or even other applications.
Process Management: the use of Scada and SDCD control systems allows the decentralized control of industrial processes. The data provided can be considered together to allow
effective and integrated of the entire Industrial Process.
Business Management: is the integration of factory floor information and individual management data from each controlled process with the company’s corporate data, administrative and financial aspects. The data and information can be used by client applications to optimize the management and integration of the entire process of manufacturing.
Architecture of OPC applications:
OPC ™ - OLE for Process Control, implements two large modules: OPC Server and OPC Client. While the OPC Server specifies standard interfaces for direct access to equipment or applications, the OPC Client specifies the default interface for applications to access the collected data.
There are three type of OPC data servers:
Data Access Server: direct access to equipment data;
Alarm & Event Server: notification mechanism for OPC clients for specific events and alarm conditions;
Historical Data Server: reading, processing and editing historical data.
OPC applications are written in several languages, such as Visual Basic, Delphi, Power Builder, etc. The OPC servers are written in C or C ++, taking advantage of the encapsulation characteristics of these languages, providing “objects” that can be accessed through any application
All specifications have been made to facilitate the development of OPC servers and can also be written in another language.
Access to OPC servers is done through the OLE / COM ™ and OLE / DCOM ™ components provided by the Microsoft ™ Windows ™ operating system.
(OLE) - Object Linking Embedding:
An object is an information unit that can be created and manipulated by users. It has intrinsic behaviour specified by its type, with its own commands and facilities. In other words, objects are data/software modules that can be included in software packages. They can be LINKED or EMBEDDED.
Linked Objects: Stored separately and can be “partitioned” by multiple applications;
Embedded Objects: are stored together with the applications. In this case, they are for the exclusive use of the same ones.
Benefits of using OPC:
Simple to develop;
Flexibility to “accommodate” the features of multiple manufacturers;
High level of functionality;
Enables efficient operation.
Hardware manufacturers must only develop a set of components to access their equipment;
Software developers do not have to rewrite drivers because of changes in equipment;
Users have more options to develop international and integrated systems;