Small smart distributed control system
Contents
1. and the maxim speed is 1OMbps e The distance of the bus is long For example it can transmit data for 1200 meters by the speed of 90Kbps e It has the strong ability to eliminate common mode disturbance because each signal is transmitted in a balanced data transmission system e Each generator or driver can drive up to 32 receivers Authorized licensed use limited to UNIVERSITY OF PLYMOUTH Downloaded on September 21 2009 at 10 13 from IEEE Xplore Restrictions apply Proceedings of the 4 World Congress on Intelligent Control and Automation Figure 2 Typical RS 485 two wire multi drop network Because of the above advantages RS 485 is always chosen to transmit data in the industrial field control system When construct an RS 485 network it is necessary to have a termination match the impedance of a node to the impedance of the transmission line being used When those impedances are not matched the transmitted signal is not completely absorbed by the load and a portion of it is reflected back into the transmission line The method to terminate data lines is to add a resistor in parallel with the receiver A and B lines in order to match the data line characteristic impedance specified by the cable manufacture 1202 is a common value ADC 106 RS 232 to RS 485 converter is made by Atronix Inc The converter can be plug into RS 232C serial port of standard DB9 pins and be supplied power by TXD DTR and RTS signals The power volt2. at the same time Then each controller will compare the received address with its own address If the address of the controller is the same as the received address the controller is connected and the other controllers are isolated from the network And now the network includes only the master node and the connected slave node so they can communicate with each other The communication program flow chart is shown in Figure 4 IV DESIGN OF SMART CONTROLLER The basic controller is the core of the hardware and the software of the whole control system Whether the design of it is good or not will influence the usability stability and the ability of real time response of the DCS To meet the needs of the real time response and the handling of TABLE I The format of the data package Destinat ion address Authorized licensed use limited to UNIVERSITY OF PLYMOUTH Downloaded on September 21 2009 at 10 13 from IEEE Xplore Restrictions apply 1977 1978 Proceedings of the 4 World Congress on Intelligent Control and Automation June 10 14 2002 Shanghai P R China data in large quantity we design a smart controller based on double MCUs One MCU deals with data sampling and real time control and the other deals with Disable interrupt save PSW data transmission The data exchange between the two CPUs is through the dual ram IDT7132 There are 8 analog input channels 6 analog output channels including 2 PWM c
3. 1976 Proceedings of the 4 World Congress on Intelligent Control and Automation June 10 14 2002 Shanghai P R China Small Smart Distributed Control System Yirong Yang and Shanan Zhu Dept of System Science and Engineering College of Electrical Engineering Zhejiang University Hangzhou P R China 310027 E mail yangyirong cee zju edu cn and zsa cee zju edu cn Abstract distributed control system DCS based on RS 485 network This paper presents a small scale smart It discusses the network construction of the distributed control system the characteristics of RS 485 how to construct typical RS 485 two wire multi drop network and the details of the communication protocol The smart controller based on dual MCUs can execute many kinds of the advanced control algorithms downloaded from the operating station The controller has strong ability to deal with real time response and great capacity of data processing because of the dual MCUs structure The control is stable and flexible because the whole program which user has configured in the operating station is downloaded into RAM The independent watchdog circuit is also designed I INTRODUCTION Distributed control system DCS is a very useful advanced automation device but its price is very high Although the DCS manufacturers in the world produce different kinds of small scale DCSs the system is also expensive to the small enterprises in the developing country To meet t
4. MOUTH Downloaded on September 21 2009 at 10 13 from IEEE Xplore Restrictions apply Proceedings of the 4 World Congress on Intelligent Control and Automation June 10 14 2002 Shanghai P R China 1979 V CONCLUSIONS From above discussion it is clear that the controller has vol 32 no 9 September 1985 pp150 152 these advantages 2 Michael Babb Distributed Process Control System Integrates The controller has good performances because of its Process Design and Control Control Engineering vol 32 no 12 dual CPU structure November 1985 pp 81 The controller is flexible because the whole program is downloaded from the operating station 3 RS 422 and RS 485 Application Note B amp B Electronics Mfg Co The watchdog circuit MAX705 is independent Inc October 1997 which can not only monitor the executing program but also monitor the power supply The circuit significantly 4 Guo Moufa and Wang Shaobo The Design of RS 485 Network improves system stability and Its Applications in Industrial Monitoring Systems Journal Of VI REFERENCES Fuzhou Universtity Vol 27 No 1 1999 I EORGE J BLICKLEY Distributed Control Systems New and Improved at ISA 85 Control Engineering 5 8x196kc kd Users Manual Intel Inc 1992 Authorized licensed use limited to UNIVERSITY OF PLYMOUTH Downloaded on September 21 2009 at 10 13 from IEEE Xplore Restrictions apply
5. age must be more than 5v The network interface of the basic controller is MAX485 which is low power transceiver for RS 485 Controlling the COMS chip is very simple Driver Enable DE and Receiver Enable RE pins are included on MAX485 Usually one of the output ports of the controller is connected to both DE and RE pins When the logic of the _ port is low the serial port is in the state of receiving If sending the data the output port logic must be made high The typical operating circuit is shown in Figure 3 Figure 3 Typical operating circuit of MAX485 June 10 14 2002 Shanghai P R China Network Communication Protocol The communication system between the PC and the controllers is strictly the master slave type system in broadcasting mode The slave nodes are not permitted to transmit data without a request from the master and do not communicate with each other The communication between the slave nodes is not direct The message must firstly be stored into the master node and then be forwarded to another slave node Each slave must have a unique address so that it can be addressed independent of other nodes The baud rate is 9600bps The data frame consists of ten bits a start bit 0 eight data bits LSB first and a stop bit 1 The data is in package form and the format of the package is shown in Table I PC or IPC broadcasts the address of the controller to be connected and all controllers receive the address
6. hannels 16 digital input channels 16 digital output channels and 2 pulse input channels Its block Read the data in SBUF diagram is shown in Figure 5 The master CPU deals with data sampling and signal processing and receives the Taig ee seination Address the same as the address of the controller configuring program downloaded by the operating station Because the program downloaded form the PC executes in RAM the control of the system is very flexible The controller can execute advanced control algorithms And the functions of modifying parameters on line and giving an alarm can be included also Therefore the controller can be made smart The slave CPU is used for communication Send error message It can receive the message from the operating station and According to the control bytes which PC need send then send the message to the master CPU If the master CPU sends data to the PC it must send the data to the slave CPU first So the message exchange between the PC send affirming message again and the master CPU must pass the slave CPU Pop PSW enable interrupt Figure 4 Flaw chart of communication program Hardware monitoring circuit WDT MAX705 Digital Interface RS 485 80C196KC 80C196KC slave CPU master CPU Analog Interface Figure 5 Block diagram of the smart controller interface Authorized licensed use limited to UNIVERSITY OF PLY
7. he needs of the small enterprises we design a small scale smart distributed control system which is cost effective II SYSTEM ARCHITECTURE The whole system includes a PC or an IPC and several basic controllers The PC as the operating station is used to configure function blocks and monitor the control process Basic controller equipped with double CPUs is used to sample data and execute control algorithms The communication system adopts EJA TIA 485 Standard which is represented by RS 485 The above elements constitute the small scale DCS The system architecture is shown in Figure 1 The operating station can be an 0 7803 7268 9 01 10 00 2001 IEEE PC OR IPC communication interface controller controller industrial computer with RS 485 interface or a PC with a RS232 RS485 converter in the serial port We select the ADC 106 interface converter made by Atronix which can Figure 1 System block diagram transfer the signal transmitting in an RS 232 serial port into the balanced half duplex RS 485 signal There is also an RS 485 interface which adopts MAX485 transceiver made by MAXIM Corporation in each basic controller Ill COMMUNICATION SYSTEM Elements of the Communication Network The data transmission of the whole system is in an RS 485 system Fig 2 is an example of a typical RS 485 two wire multi drop network The characteristics of RS 485 is as follows The speed of RS 485 bus is quick
Download Pdf Manuals
Related Search