The Research On Field Bus Technique

Firstly a brief discussion about Profibus protocol is presented in this paper, then the author summarizes the method of Profibus protocol realtime performance calculation with emulation result by example through deep analysis of Profibus data link medium access control (that is MAC), which illustrates the relation among parameters like Profibus realtime performance, lenghth of message frame and number of master station.This paper shows how to realize communication between master station and slave station by example of Profibus —DP communication between Siemens DC driver 6RA70 and S7 —300PLC, on the basis of which proposes a method of development and realization of intelligence slave station used by Siemens chip SPC3. Then a discussion about the features of the hybrid medium access protocol based Profibus and the centralized medium access protocol based FF (Foundation Fieldbus) is presented, network performance metrics of FCS (Fieldbus Control System) are proposed systematically, the quantitative and qualitative analysis for Profibus and FF is conducted and compared in following performance aspects: the message frame format, data coding efficiency, deterministic and bounded characteristic of periodic messages,and the relation of real rotation time ,throughout, delay of a periodic messages, network utilization, network efficiency and message finish rate with traffic load. The analyse results indicate that FF is superior to Profibus for the application in which periodic messages traffics have stringent time constraints.These results will set up a good basis for further improvement and realization of Profibus and FF systems.