Research And Implementation Of The Fieldbus User Layer Protocol

FieldBus is a system which implement serial, digital, bidirectional, multi-noded data communication between PC-based measuring and control devices, and it is applied in factory floor. OPC specifications and IEC 61499 standard both are protocols of User Layer of FieldBus Control System(FCS), and both are based on software component technology.After introduction to componen object model and OPC specification, design principles, methods and steps for OPC server are discussed and severs designed with SmartOPC, OPC Genie and LightOPC tools are submitted. Configuration software acquires real-time data from data acquisition module, using the OPC servers as intermediate entity. The results shows that OPC server can fulfill the function of allowing monitoring and control software(e.g. SCADA, HMI) to access filed devices in a consistent manner. OPC makes the seamless integration of monitoring&control software and devices, and repetitive work on developing drivers for different vendors' devices is avoided.It is easy and fast to design servers using server development tools. According to requirements of portability and generality for designing OPC server, a design principle for development library is arrived at. At the basis of LightOPC library a custom library in the form of DLL is designed by Visual C++. The designing method of standard COM/OPC interfaces and API of the library are provided, as well as steps for using the library and server instance.Architecture, advantages and design patterens of IEC 61499 standard (Functions blocks for distributed industrial-process measurement and control systems) are introduced, and a simulation instance developed by FBDT under MVC mode is provided. The paper discusses how to implement the architecture using COM technology under Windows platform. Comparison between OPC and IEC 61499 are made in scope of technology, structure and function under PCS context.