The Research And Realization Of OPC Server In Data Access

As technologies of microelectronics, communications and network developed rapidly in these years, the nonstandard data access protocols in the traditional industrial control area made all kinds of intelligent control devices become"isolated islands of information", that blocked the development of control area in the networking and intelligentization. In order to break the bottleneck of the data access, the OPC technology was invented. It provided a unified standard specification of data access for the control area to settle some problems of resources wasting and communication difficulty caused by varied drivers. The OPC technology is conductive to promoting the networking integration of intelligent devices, and good for the enterprise to realize the longitudinal connection from the layer of device to layer of the process control and the business management decision, which leads to realize the automation network control system of the whole enterprise.Firstly, this paper studied the data access specifications of OPC DA and OPC XML-DA deeply, analyzed the communication theory and process of these two specifications, and found that there were limitations of platform and network in the OPC DA communication which is based on the COM theory. But the XML-DA which is based on the standardized technology of Web Services, XML and SOAP, can communicate cross over firewall, system platforms, and programming languages. Then, according to XML-DA specification, the paper used tools of Visual C++ and gSOAP to design and implement the OPC XML-DA Server, and applied it into the remote control system of environment. It is worth mentioning: predecessors'implementations of XML Server are mostly based on the conversion of the OPC DA Server, but my paper is the original implementation of XML-DA Server.There were some conclusions and results below through research and practice.1. OPC DA specification packages data into a good three-tier data structure, and we can apply this data structure into XML-DA Server to manage data efficiently.2. There are limitations of platform and network in the communication of OPC DA, but XML-DA can communicate cross over firewall, system platforms, and programming languages, and it becomes the real communication standard in industrial control area.3. According to the eight service interfaces provided by XML-DA specification, the paper combined with OPC DA data structure, used tools of Visual C + +6.0 and gSOAP to implement the original shape of XML-DA Server which can be reused in any other fields.4. Applied the XML-DA Server into the control system in environment, and summarized that there are four advantages using XML Server in the control system: openness, connectivity, portability and information sharing.