Study Of Distributed Measurement System Based On CAN Bus Technology

Field bus is a digital, bi-directional and multi-branch communication network that connects field equipments and automatic system. As a product integrating technology of computer, communication and control, the field bus featured with opening and distribution has been one of the key technologies in modern automatism field. As one of the field buses, CAN (Controller Area Network) is a serial communication network that supports distributed and real time control effectively. CAN very fits interlinkage of monitor and control equipments in industry process and has been well accepted as the most perspective field bus. A distributed measurement and control system was developed based on CAN field bus. The technologies in some fields including computer, control, communication, network and circuit design were used which enable a comparatively rich functions in monitor and control, in addition to stable performance and friendly interface. Research content includes the research on hardware of node and CAN-PC interface card, software both running on node and interface card, and software running on PC for monitor and control of CAN network. PIC16F877 single chip computer and MCP2510 CAN controller are the main elements of Node and Interface Card. Every node has 4 AD inputs and 8 switch outputs. The maximum 110 nodes on a CAN bus communicate with PC through interface card. Monitor and control software running on PC is designed with object-oriented method. The physical existed node is mapped to an instance of node class, so the monitor and control to node are also mapped as the calling of node class's methods. All data and setting are supported by database. The function of online adding and removing of nodes on CAN bus are achieved by event trigger mechanism. The PC software can monitor all sensors and can show, print the history curves of which. PC software also can control the 8 switches of all nodes by call the remote control method of node class. The adjustment of sensor is implemented in PC instead of node that overcomes the disadvantages of inconveniency and inefficiency of writing adjustment data to node. This system is a universe product that can be used in varied situation with different sensors. The main content of this thesis is as following: In the first chapter of this paper, the conceptions and features of distributed system, field buses are introduced. The traditional RS232 and RS485 serial communication standard are also discussed in this chapter. In the second chapter the CAN hierarchy structure, frame structure and communication principle of CAN technology are introduced. The structure of distributed sensor system is formed according the features of CAN. In the third and forth chapter, the circuits design and chips selection of both interface card and node, plus the design of indispensable node software, interface card software and PC's monitor control software based on CAN field bus are researched. In the final part of this paper, a summary of the project is made. The issues about how to perfect this system and development of relative theory and technology are also been discussed.