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Function of PLC in ProfibusDP single master station system run -
a, Profibus overview
Profibus is by SIEMENS company launched an open field bus standard, in 1989 became the standard German DIN19245, become the European standard EN50170, 1996 in December 1999 is accepted as part of the international standard IEC61158. Profibus is one of the Europe and the world the most widely used bus system, his speed of low cost, almost all of the PLC controller and much automation peripherals products provide Profibus interface.
Profibus according to different applications to provide three compatible version: ProfibusDP, ProfibusFMS and ProfibusPA.
ProfibusDP for field level high speed data transmission between the distributed automation peripherals ( The meaning of DP for decentralized peripherals) 。 His architecture including the ISO/OSI reference model layer 1, 2, and the user interface, transmission technology using RS485 ( Known as the H2) Communication, this structure can guarantee the real-time and low cost of system implementation. Use defined in the user interface user and the system application function and describe the scene equipment usage behavior of how it works.
ProfibusFMS（ 现场总线消息规范) Is the site level and unit level communication general solution, mainly to solve unit level between the master station ( PLC controller and PC) Communicate with each other, so the advanced features is more important than the speediness system response time. FMS USES the ISO/OSI reference model,2,7 layer 1, layer and ProfibusDP compatible with 1, 2, 7 layer includes the application protocol and provides a wide range of communications services functions to the user.
ProfibusPA is on the basis of ProfibusDP through optimizing, extension, and is mainly used in chemical and other occasions, with relatively high security requirement communication using extension ProfibusDP agreement. Transmission technology to switch to IEC11582 ( Called the H1) Nature to ensure security and make the field device through the bus power supply, through piecewise coupler, can conveniently and ProfibusDP, ProfibusFMS are linked together.
2, Profibus communication protocol
Profibus communication protocol by the ISO/OSI reference model level 2, level 2 in the Profibus called FDL ( 现场总线数据链接) 。
Profibus bus equipment includes two categories: master station and from the station. Standing in a limited time, The token hold time TokenHoldTime) Inside has control over the bus, then the main data can be sent from a station or request data from the station. From the station has no control over the bus and just response to a master station requests or confirm the main data. So Profibus communication protocol including token passing protocol between master station and the main, from standing between the master-slave protocol.
token passing protocol to ensure that each host have enough time to fulfill his task of communication, the token in all the main loop longest is certain of the week. Master-slave protocol ensure that standeth in the token hold time and communication from the station.
3, ProfibusDP single master station system
ProfibusDP allows a single host or host system. More host configuration, the master station consisting of from standing and independent subsystems, involving the token passing. In field bus systems, in many cases is composed of PLC as the controller and the main single master station system, the system if not closed, Run independently without data exchange with the outside world) , likely by ProfibusFMS or other field bus is connected to the workshop level unit such as a larger network, in addition to this most likely PLC with PC by serial RS232 machine ( Monitoring layer) Communication, as shown in figure 1.
in most of the temperature control, ingredients such as system, sensor sampling rate> 10 ms, generally from the station number is less, the bus data transmission speed of 500 KB/s or less, can use PC to replace PLC as the controller and the master station, using low cost between PC and ProfibusDP RS232 / RS485 converter connection, to save expensive PLC, as shown in figure 2. On the software, because of the single master station system does not involve the use of token passing, can easily write on PC compatible ProfibusDP the single main program of the agreement. 6
RS232 using only the TXD, RXD three root signal wire and GROUND. Each frame eight data bits, parity, 1 stop bits. 9600 b/s data transmission rate.
2, as the lower machine inquiry, set up the stand from
program block diagram as shown in figure 3
3, as a stand from PID regulator to control the output
the part program block diagram as shown in figure 4, the specific procedures slightly.
as process monitoring layer, also can use cycle each from polling station, PID program is only for one from the station. 软件当然也可使用Simatic WinCC组态、VC++6. 0 of the graphical interface PC application to monitor and control the double function. Five, the conclusion
programs run on figure 2 PC in the system, and using ASIC chip agreement ProfibusDP from station can very good communication, the PID output program in belt scale ingredients the same accuracy reached and PLC control, in some ProfibusDP single master station system is verified the feasibility of the PC to complete the function of PLC.
Anyone who has seen the latest programmable control systems plc manufacturers in operation cannot help but be impressed with how far the technology has progressed over the past few years.
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