Research Of OPC DA Server Based On Modbus/TCP

Nowadays, more and more hardware and software are used in industry control field and the system integration becomes more complex than ever. In traditional industrial co ntrol field, in order to access field data, software manufactures have to develop a special driver for each given device. Then lots of problems are produced such as repeated dev elopment, driver incompatible, access violation and bad adaptability of drivers after updat ing the hardware, so it is very necessary to develop a uniform and universal data access standard. OPC (OLE for process control) standard success to solve the problem that har dware and software can’t communicate rightly. Among existent industrial systems, Modbu s/TCP is a variant of the Modbus family and it covers the use of Modbus messaging in an Intranet or Internet environment using the TCP/IP protocols, it has become the defau It standard for industrial communication via Ethernet as a result of its open, easy-to-unde rstand and stable specification. This paper study the OPC Data Access Server based on Modbus/TCP, the server can provide data integration and interoperability between field la yer and application software fore-and-aft, and then get the information integration of cont rol system.This project is based on the background of renovation of communication server of c omputer supervisory control system in a certain sewage plant. It aims to build a supervis ory control system for sewage on the basis of both OPC and Modbus/TCP Ethernet field bus technology. The establishment of this system is mainly because of the disunity of d ata access interfaces and instability of the multi-site equipment connection, etc. It solves the date communication issue between communication server in the supervisory system a nd site plant and gives the function of supervisory from system to site plants like PLC and also unattended operation so that it achieves seamless integration further.The article adopts WTL technology to develop OPC data access server based on M odbus/TCP. As a communication server of the supervisory control system in a certain se wage plant, this server makes it possible the data collection and control of site plant thr ough supporting the supervisor of Modbus/TCP site plant and analytical processing to M odbus/TCP data packet. The article also adopts OPC standards to solve the compatibility issue of different hardware facilities, provides data access approaches for upper machine like upper data management、supervisor、maintenance and warning so that this communi cation server will be an information integration system built in unity with site plant and upper machine. Then, through testing the server by OPC client, the system model of cr oss platform communication is finally built based on TCP/IP.