The specification of OPC identifies a constant terminology to classify a variety of entities concerned. The best comparison to OPC method of data representation is that of a hierarchy of file system. OPC defines it as Address Space of OPC. In this address space each entity can be individually acknowledged by its full-path.
Address Space of OPC is hierarchical. It begins with a root. After that there are valid folders and sub folders. The nodes of leaf are OPC Tags or Items. Usually your actuators and sensors form the nodes of leaf. This is a vital point to know and you will use some time on it. For instance, you have a tool that can detect Pressure, humidity, and temperature. Then these features are usually mapped as nodes of leaf under some folder or subfolder hierarchy. You will see what that hierarchy can be in an instant. If you have an actuator then that also turns into a node of leaf. You can write to values of Turn_ON_Boiler of 1 or 0 for instance, and required action will be taken, of course you just thought that your control mechanism hardware performs this way. You can interpret from Temperature to identify value of sensed.
The sub folders and logical folders are utilized to stand for state of your system of Industrial Automation. This design can essentially map to some geographical setup or even physical configuration. Let's use some time to recognize this one as well. For instance, you have a channel of Ethernet communication to which a meter of wireless is linked. And inside meter of wireless, there are two classes Channel1 and Average. These sub folders and folders are very effectual means of group your process control values and parameters.
This space of address is available to all OPC server clients. The OPC clients can be easy spread sheets like Excel, the history of process that maintain record of data coming from a variety of industrial plant entities. Each client can make a logical entity defined as group inside server of OPC. every OPC Group can include an OPC Items set.
Item reading of Synchronous & Asynchronous OPC
The specification of OPC supports the synchronous as well as asynchronous writing and reading on devices hardware. While not all devices of hardware operations are fast enough, the mechanism of asynchronous writing and reading to a tool creates very handy.
Specifications of OPC
The Foundation OPC is in charge for releasing and maintaining new specifications. It is a body built up of industry specialists, corporations that manufacture products of OPC and organizations that use products of OPC. So far Foundation OPC has launched below specifications.
• OPC-DA
It is provides admittance to real time data. You can question the majority recent values of density, temperature, acceleration, pressure, and other kinds of data process control from server of OPC-DA (Data Access).
• OPC-HDA
It is used to recover the process data history for analysis. This data is normally saved in databases, archives, or remote systems of telemetry.
• OPC-AE
The servers of OPC AE are utilized to switch over and recognize process events and alarms.
• OPC-DX
It defines how one server of OPC swaps over data with other servers of OPC.
• OPC-XML (XML Data Access)
It defines data representation and schema format according to standard of XML. It makes it possible to manipulate and share process control data across all operating systems such as Solaris, Unix, Windows, etc.
The majority newly Foundation OPC has launched a draft for Unified Architecture of OPC those efforts to provide even more process control data integration and software with other software system industries such as ERP.
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