Research On Real-time Performance Of Mono-Master PLC Control System Based On PROFIBUS

The research topic, involved in this paper, comes from the need of actual project.This paper deals with real-time performance of the bottom industrial control network,which provides basis for users constructing the whole control system.A typical mono-master control system, composed of PLC and PROFIBUS, isconsidered as the research background, which is used commonly in automationengineering. Based on deep analyses on several key technologies, such as the cyclicscanning mechanism of PLC,data transmission services and MAC protocol ofPROFIBUS, message transaction cycle time formulae are given for data exchangesbetween master and slave in normal run state. Furthermore, the response time betweenmaster and simple or intelligent slave, is analyzed respectively.Then the time delay characteristics of the hybrid network of PROFIBUS DP/PAareseriously analyzed, and a method of inserting extra idle time is put forward, whichimproves the response speed between the master in DP segment and the slave in PAsegment.Finally, for a typical engineering system, given I/O response lag of PLC and thetime delay characteristics of the hybrid network, real-time performance of the controlsystem is analyzed. The application in the project shows that the analytical method is ofgreat value in practice.