王曦英文翻译最终版Word下载.docx

1、 Programmable Logic Controller （PLC）, Automation, Microcontroller Applications, Industrial Electronics, Digital Control, On-Off Control, Digital Electronics1. INTRODUCTION1.1 PROBLEM DESCRIPTIONWe all know that industrial automation is the backbone of a nation for its prosperity since, it reduces th

2、e production cost many folds and also increases productivity. For this purpose WLC （i.e. Wired Logic Controller） was introduced. It was the first step in the industrial automation. Later on microcontrollers were introduced which had the advantage of greater flexibility over the WLC.Eventually, a ver

3、y sophisticated version of a controller was introduced with a very large I/O handling capability and extreme flexibility called the Programmable Logic Controller, commonly called the PLC. Siemens introduced many series of controllers with different capabilities. One of the first series was the SIMAT

4、IC 5 Controllers. The PLC available to us is the S5-100U-100. Later on Siemens introduced the SIMATIC 7 series of controllers and now, we also have the S7-314IFM PLC.The PLCs are not alien to the industries of Pakistan. They have been around for quite a long period and are being employed extensively

5、. Even though the demand of this product is considerable here, there has been no effort to develop it indigenously. Since there had been no development in this field in our country and being a requisite of the nation, so as an exercise of Logic Design, Digital Electronics, Interfacing and Software E

6、ngineering, we undertook this task of making a PLC better than the S5 controllers and comparable to some extent to the S7 controllers. The PLC that we have designed can also be upgraded to supportRemote Data Acquisition.1.2 BLOCK DIAGRAM AND BRIEF DESCRIPTIONThe complete general block diagram of the

7、 PLC is depicted in Fig.1-1. Just like the SIMATIC 5 systems, our PLC can also be broadly classified into three distinct units:a. CPUb. Bus unit, andc. Modules （I/O and function）Fig.1-1 Block diagram of the PLCEach unit can be discussed as follows:1.2.1 CPUThe CPU, as the name suggests, is the brain

8、 of the PLC system. Without its brain, the PLC simply cannot function.In our system, the CPU comprises of two ATMEL 89C52 microcontrollers. As in every multi processor system, one is the master and the other is the slave. The functions performed by the master or the controlling unit （Fig.1-1） can be

9、 summarized as follows: Monitor and control the operating modes of the PLC using the operation controls. Configure the PLC modules. Check program integrity by monitoring scan cycles.The slave microcontroller （executing unit, Fig.1-1） functions to run the user program. It is responsible for: Taking t

10、he appropriate actions during startup. Issuing the signal at the start of every scan cycle and the subsequent addressing and transaction of data with the modules. Handling the counters and timers.The CPU section also has the responsibility of communicating the programming device i.e. the computer th

11、rough a serial port. The communication channel works according to the semaphore algorithm （commonly known as token algorithm）. It is to be noted here that the communication link currently does not function, as mentioned earlier, because it was a part of the planned GUI, which has not been implemente

12、d due to the constraint of time.1.2.2 BUS UNITThe bus unit functions similar to the motherboard in a computer. The bus unit that we have constructed holds up to 4 modules and the CPU; we named it the main bus unit. Moreover, the bus unit also carries the extension connector by which other bus units

13、can be cascaded to increase the I/O handling capability of the PLC. The bus units that will be cascaded will not have a slot for connecting the CPU; only modules can be connected.The main function of the bus unit is to buffer all the signals i.e. the data buses, address buses, and the control signal

14、s, to eliminate the loading of the CPU. This function is also performed by the main bus unit but this also performs an extra function during the configuration stage. The bus unit controller, see Fig.1-1, selects each slot one at a time so that it can be configured for the module connected in it and

15、also sends a signal to the controlling unit when all the slots have been selected and configured once.1.2.3 MODULESThe modules serve to provide the interface of the PLC with the plant to be controlled. The modules, which we had designed were digital input, digital output, analog input and analog out

16、put modules （verified using OrCAD PSpice）. But we only managed to manufacture the digital input and output modules, each capable of handling 16 devices. The standards of the modules are similar to that of commercially available modules.The modules are equipped with an address decoder circuit, which

17、is common in all the modules, as the circuit has been designed to support auto configuration.1.3 POSSIBLE SOLUTIONSNow that the overview of the project is present before us, we will take a look into the possible solutions that came to our mind when we commenced brainstorming. The ideas can be listed

18、 as follows along with their supporting and disagreement comments. Use of a single processor/microcontroller was the first idea that came to mindbecause it was most simple and easy to implement. The problem with such an idea was that we were striving for a good scan time due to which we needed a fas

19、t processor （which was unavailable） or had to go for multiple processors. The use of microprocessor instead of a microcontroller was also among the options because we have been taught the assembly language of this processor and we were well aware of it. The drawback of such a selection was that in a

20、 PLC, bit operations are plenty while the microprocessor instruction is not very powerful for such operations. Using a 16-bit microcontroller for ease of work was a great idea but its materialization was not possible as it was not available here. After all these options, we were left only with the o

21、ption of using two microcontrollers in tandem to achieve our desired task.1.4 REASONS FOR SELECTIONOf all the above solutions mentioned above, we decided to implement the multi processor CPU with the bus unit scheme for connecting the modules. The advantages, which also form the reasons for the sele

22、ction of this design, are enumerated below. This solution was the first seemingly feasible solution that came to our minds. During the course of work, many more came but then it was too late. The design was based on equipment and technology easily available in our city. The use of microcontroller in

23、stead of a microprocessor is justified by the fact that the microprocessor is incapable of bit operations, which are numerous in a PLC. A fast microcontroller was unavailable hence we decided to distribute the work load and run tasks simultaneously by using two controllers so that the speed is not c

24、ompromised. The auto configuration feature allows the design of the modules to be quite generic as the address decoding section is identical hence ensuring ease of manufacture. The use of the bus unit allows cost effectiveness as specialized circuits in each module are not required as found in the S

25、IMATIC 7 controllers.2. ANALYSIS AND SIMULATIONSince our system is a digital system based on microcontrollers, it was not possible to obtain its mathematical model. Instead, we have simulated our circuit design with all the real life limitations in OrCAD 9.1 PSpice. The computer hardware simulation

26、results and their analysis are discussed below.2.1 COMPUTER SIMULATIONS - HARDWAREThe simulations were carried in different stages; the auto configuration process, in which the control word is read and then the appropriate address, is assigned to the module. Once this was tested, the complete sequen

27、ce of reading data from a digital input module was tested. Similarly, the sequence of writing to a digital output module was also tested.Before discussing the processes, one thing that must be stressed is that the signals used for testing the performance of the circuits were constructed using actual timing delays that would be introduced by the microcontrollers. All the propagation delays, pulse widths, etc. have been carefully implemented so that our simulations are as near to practical results as possible.2.1.1 THE AUTO CONFIGURATION P