What is OPC
What is OPC?
Imaging Chinese want to talking with Iranian ! they do not understand each other ! so people of the world make a decision to all the people of the world speaking English together and English become the global language. OPC work like English for industrial automation.
OPC is the world’s most popular standards-based data-connectivity method. It is used to answer one of the automation industry’s biggest challenges: how to communicate between devices, controllers, and/or applications without getting caught up in the usual custom driver-based connectivity problems.
In the past, OPC was a collection of software interfaces for data exchange between PC applications and process devices. These software interfaces have been defined according to the rules of Microsoft COM (Component Object Model) and can therefore be easily integrated into Microsoft operating systems. COM or DCOM (Distributed COM) provides the functionality of inter process communication and organizes the information exchange between applications, even across network boundaries (DCOM). Using mechanisms of the Microsoft operating system, an OPC client (COM client) can use it to exchange information with an OPC server (COM server).
The OPC server provides process information of a device at its interface. The OPC client connects itself with the OPC server and can access the offered data.
The use of COM or DCOM causes OPC servers and clients to run only on a Windows PC or in the local network and that the communication to the respective automation system has to be realized mainly via proprietary protocols. Additional tunneling tools often have to be used for the network communication between client and server in order to get through firewalls or to avoid the complicated DCOM configuration. The interface can furthermore only be accessed natively with C++ applications; .NET or JAVA applications can only gain access via a wrapper layer. In real-life situations, these restrictions lead to additional communication and software layers which increase the configuration workload and the complexity.
Due to the widespread use OPC, the standard is increasingly used for the general connection of automation systems and no longer only for the original application as driver interface in HMI and SCADA systems to access process information.
To solve the mentioned restrictions in real-life situations and to fulfill the additional requirements, the OPC Foundation has defined a new platform in the last five years, called OPC Unified Architecture, which offers a uniform basis for the exchange of information between components and systems. OPC UA will also be available as IEC 62541 standard and therefore forms the basis for other international standards.
OPC UA offers the following features:
Summary of all previous OPC features and information such as DA, A&E and HDA in a generic interface.
Use of open and platform-independent protocols for inter-process or network communication.
Internet access and communication by means of firewalls.
Integrated access control and security mechanisms on protocol and application level.
Extensive representation options for object-oriented models; objects can have variables and methods and can trigger events.
Expandable type system for objects and complex data types.
Transport mechanisms and modeling rules form the basis for other standards.
Scalability of small embedded systems up to business applications and from simple DA address spaces up to complex, object-oriented models.
Benefits of using OPC Connectivity
At first glance, trading a single Custom Driver for two OPC components (OPC Client and OPC Server) may not look like much of an improvement but as experience has shown, it is. Following are some key benefits of using OPC:
An OPC enabled Application can freely communicate with any OPC-enabled Data Source visible to it on the network without the need for any driver software, specific to the Data Source.
OPC-enabled applications can communicate with as many OPC-enabled Data Sources as they need. There is no inherent OPC limitation on the number of connections made.
Today OPC is so common that there’s an OPC connector available for almost every modern and legacy device on the market. It’s easy to get started using OPC.
OPC-enabled Data Sources may be swapped out, exchanged, or upgraded without the need to update the drivers used by each application (Data Sink) communicating with the Data Source via OPC. Only the OPC Server for that Data Source needs to be kept current.
Users are free to choose the best-suited devices, controllers, and applications for their projects without worrying about which vendor each came from and whether they will communicate with each other… intercommunication is now assumed!
What types of Data does OPC Support
The most common types of Automation data transferred between devices, controllers, and applications break down into three broad categories:
Real-time data
Historical data
Alarm & Event data
Each of the above also supports a wide range of value types. Some common examples of these data types are integer, floating point, string, date, and various array types to name a few. OPC addresses the challenges of working with these different data categories by independently specifying how each one is to be transmitted via the OPC Client and OPC Server architecture.
The three OPC specifications corresponding to the three data categories are:
OPC Data Access Specification (OPC DA) – used to transport real-time data
OPC Historical Data Access Specification (OPC HDA) – used to transport historical data
OPC Alarms & Events Specification (OPC A&E) – used to transport alarming information
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