Study On Real-Time Problem From Fieldbus To Industry Ethernet

With the rapid development of microelectronics, computer and communications, 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. 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.Phylogeny of industrial control network is presented at the beginning of the dissertation. In the body of the dissertation, existent real time problem and research status quo are indicated, and the real time problem of fieldbus and industrial ethernet are researched. The major contributions of this dissertation are as follows:1. In the communication of fieldbus, real time schedule process and real time schedule table of filedbus are kernel and key problems during fielbus protocol research and fieldbus device development. Taking Foundation Fieldbus (FF) for example, the real time schedule mechanism of fieldbus is investigated, the implementation of communication stack is presented, the method of building real time schedule table is put forward, the schedule algorithm and the algorithm schedulabilty of real time schedule table are researched.2. In the industrial control application, waste of filedbus bandwidth is serious when there being some aperiodic communications with critical time constraint. To resolve this instance, bandwidth allocation of fieldbus is researched based on priority mechanism, the static and dynamic bandwidth allocation algorithms are proposed and compared by performance. Taking Foundation Fieldbus (FF) for example, the optimization bandwidth algorithm of fieldbus is proposed.3. Real time characteristic of ethernet is analyzed based on industrial control application. End-to-end delay of ethernet is analyzed, the expectation expression of queue delay and calculation procedure of send delay and transmission delay are presented. By experiment, the influence of some factors (node numbers, framelength and communication speed) on real time characteristic of etheraet isresearched, and real time characteristic of ethemet and fast ethemet under three information releasing modes (synchronous, random and scheduled) is investigated.4. Non deterministic communication delay of ethemet which can't satisfy real time request of industrial control has become main obstacle in application on filed device layer network. To resolve this problem, some methods of improving real time characteristic is analyzed. Based on real time request of information, the solution of EPA system is put forward which can settle real time communication on filed devicelayer network. The solution of EPA system includes network communication model,communication service modes, real time schedule and clock synchronization. Finally, the practical application of EPA system is presented.5.In the industrial control application, information transmitted on control layer network has become more and more complex, requiring that communication network should satisfy real tune request diversity of information. To satisfy this requirement, a mixed schedule algorithm on switch ethernet is put forward based on information classification. According to information types, the algorithm takes different schedule algorithm which include setting priority level, modified RM schedule algorithm onhard real time information, priority level upgrade schedule algorithm. By experiment, the algorithm is validated.6. Industrial real time ethernet system which based EPA is detailedly researched The contents include system configuration, application layer protocol, communication between devices, redundance management and device descriptions.In this system, all layers network of enterprise integrated automatic system...