The Research Of The Real-time Communication Performance Of Profibus Based On Schedule-ability Algorithm

With the rapid development of microelectronic,computer and communications,the level of industrial automation is upgrading,the demand on control networks is increasing gradually,industrial control network has also constantly developed,from Distributed Control System(DCS) which based on analog signals transmission,fieldbus which is digital,intelligent and entirely disperse,to industrial Ethernet which appeared and rapidly developed in recent years. Fieldbus is a kind of distributed and feedback control system,the control loop of which is closed through real-time control network. Fieldbus changes the framework of traditional control networks,achieves real distributed control by making control functions down to the spot,and gives the instruments more functions including measurement,control,communication,remote configuration management,self-diagnosing,and so on. Profibus is the most prevalent fieldbus standards in all kinds of fieldbus standards,the application and research of which have been fully-fledged domestic and abroad. As a specific network,industrial control network has its own requests and characteristics compared with commercial network,one of which is exigent real time characteristic which requiring not only rapid transmission but also rapid response,which affects the performance of the whole control system directly. In this case,how to improve timeliness of fieldbus using good message scheduling strategy is meaningful.Message model,time and space consistency that affect real-time capability of fieldbus were analyzed,then QoS parameters that evaluate performance of fieldbus were presented. Moreover,dynamic and static message scheduling algorithms were discussed in detail. Based on the comparative study of various MAC protocols,the author has pointed out their advantages and shortcomings when managing messages with different time characteristic.Setting reasonable network parameters such as target token rotating time is very important for Profibus,which affects real-time performance and efficiency of the bus. Base on the analysis of data transmission services,MAC message processing,token circulation and maintenance mechanism of token ring,a set of approached to calculate message cycle time,token cycle time and bus efficiency were presented in this dissertation. Furthermore,schedule ability analysis of the high and low priority messages based on response time was presented. The principle of setting target token rotation time was also brought forward. The simulation results show that these approaches are very effective,and can be used to verify the rationality of network parameters and real-time performance of FCS.