Research On Real- Time Performance Of PROFIBUS

This paper, supported by the research plan in Xi'an City and some cooperation topics, comes from the need of actual project. As a bottom industrial control network, the real-time performance influences the whole function of control system directly, so the analyzing and counting of it are of great importance. While the message transaction cycle time is an important measurement to the real-time performance of PROFIBUS, so how to work it out becomes a key problem in the study.With typical distributed control system consisted of PLC and PROFIBUS, which is used commonly in automation engineering, as study background, the inside work in master station and the characteristics of PROFIBUS communication protocol are studied. Based on the characters of mono-master network, the"1-n"processing model of high priority messages is set up, subsequently, the maximal transmitting delay is formulated. While in the multi-master system, based on the analysis of different setting values of the target token rotation time, the message queuing and transmitting time are counted, later a method of calculating the message transaction cycle time of high priority message is presented. Furthermore, schedulability analysis of message and suggestion to setting the target token rotation time are also put forward.Finally, for the typical project of VD refining furnace which is based on PROFIBUS and PLC, with consideration of PLC scanning time delay, the real-time performance of PROFIBUS is analyzed. The application in project shows that analyzing and calculating of real-time performance are of much practical value.