Research On Auto-network Measurement System Based On PROFIBUS-DP

With the rapid development of computer, communication and automation technologies, networking has been the development trend of Measurement System. The mainstream in the Measurement System is the one based on fieldbus network which is a whole scattered, digital, bi-directional, multivariable, multipoint and multistation communication network connecting intelligent equipments and automatic system. Replacing the traditional analog signal (4～20 mA) with digital signal, fieldbus technology greatly fallen off the communication bandwidth and the number of cables between sensors and controllers, effectively reduced the system cost and complexity, realized intelligent distributed measurement and control, and gave a giant push forward to the technology improvement in field of water envioronment Measurement System. PROFIBUS, as one of the international specifications of fieldbus, has been used extensively in industrial automatic Measurement and Control fields.This paper firstly analysis the protocol, functions and characters of PROFIBUS fieldbus, then deeply studies its message structures, laies a foundation for realizing its functions.Facing the needs of the project, this paper designs an Auto-network Measurement System based on PROFIBUS-DP fieldbus and introduces its system constitution. To the signals of temperature, salinity, dissolved oxygen and PH value measured by the system, this paper introduces the measuring solution.The system hardware designing is focused on PROFIBUS-DP slave, including intelligent instrument periphery circuit, power circuit, PROFIBUS-DP interface mode circuit and liquid display mode circuit.While the system software designing is including protocol between intelligent instrument and interface card, data acquisition & A/D converting module, initialization and data exchange module, liquid display drive module, PLC master data processing module, WinCC configuration and other modules like serial communication and keypad input modules. Verified by testing, this system actually fulfills strong functions of PROFIBUS fieldbus, optimizes system control, improve system's performance. The system is stably and reliable, with high measuring accuracy, satisfying the project's wants.