The OPC (OLE for Process Control) specification established by OPC Task Force was officially born in August 1996. With the introduction of Microsoft companies in February 1997, Microsoft launched DCOM technology, September 1997, newly established OPC Foundation on OPC specification Conductive, add some standards such as data access, and the OPC specification has been further improved.
"OPC Based on Microsoft's Distributed Internet Application (DNA) architecture and Component Object Model (COM) technology, the .OPC specification is designed according to easy scalability, this standard makes COM technology to process control and Application areas such as manufacturing automation. "Dave Rehbein, chairman of the OPC Basics, is described in this way
OPC is a communication standard for an OLE / COM mechanism as an application. OLE / COM is a customer / server mode with the advantages of language independence, code reuse, and easy integration. The OPC specifies the interface function, regardless of the form of on-site equipment, customers access to a unified manner, ensuring the transparency of the software to the customer, so that the user is completely detached from the low-level development.
There must be an OPC interface between the application and the OPC server, and the OPC specification provides two sets of standard interfaces: Custom standard interface, OLE automation standard interface. OLE automation standard interfaces are usually used in system design.
OLE Automation Standard Interface, and OLE Automation Techniques Call, which technology is the OLE automation technique described in the next section. The OLE Automation Standard Interface defines the following three-layer interface, which is in turn contains a relationship.
OPC Server: OPC Start the server, get the starting class for other objects and services, and use to return OPC Group objects;
OPC Group: Stored by Group information consisting of several OPC Item and is used to return OPC Item class objects.
OPC Item: Stores information such as specific Item, data value, status value, and more.
Since the OPC specification is based on OLE / COM technology, the OLE / COM extension remote OLE automation and DCOM technical support TCP / IP and other network protocols, OPC customers can be physically separated, distributed to different nodes of networks. The OPC specification can be applied in many applications, such as they can be applied to get the lowest level of raw data from the physical device of SCADA or DCS systems, which can also be applied to acquire data from SCADA or DCS systems to applications. In fact, the purpose of OPC design is to obtain data from a node on the network.
