plc and its related devices should be designed in accordance with the principle of easy to form a whole with industrial control and easy to expand its functions. Here is my plc graduation design thesis for you, I hope it can help you.
plc graduation design thesis aIntroduction to the application of PLC
Abstract Programmable controllers are electronic systems that operate by digital algorithms, designed to be applied in industrial environments. Programmable controllers use programmable memory, which is used to perform logical operations, sequence control, timing, counting and arithmetic operations and other operational instructions within it, and through digital and analog inputs or outputs to control various types of machinery or production processes. Programmable controllers in industrial automation control, especially the position of sequential control, in the foreseeable future, can not be replaced.
Keywords programmable controller; analog
Programmable controller is short for Programmable Controller, often abbreviated as PC. but it is not PC as in Personal Computer. Also not only (but including) the early programmable logic controller PLC (Programmable Logic Controller), programmable sequence controller PSC (Programmable Sequenec Controller) and programmable matrix controller PMC (Programmable Matrix). Programmable Sequenec Controller (PSC) and Programmable Matrix Controller (PMC).
Programmable controllers and their related equipment, should be easy to form a whole with the industrial control, easy to expand its function of the principle of design. At present, PLC has been widely used at home and abroad in steel, petroleum, chemical, electric power, building materials, machinery manufacturing, automotive, textile, transportation, environmental protection and culture and entertainment industries, the use of which is mainly divided into the following categories:
1. Switching logic control
Replace the traditional relay circuit to achieve logic control, sequence control, can be used for both the control of a single device, but also for multi-machine group control. Such as injection molding machines, printing machines, stapling machines, combined machine tools, grinding machines, packaging production lines, plating lines.
2. Industrial process control
In the industrial production process, there are a number of such as temperature, pressure, flow, level and speed and other continuously changing quantities (i.e., analog), the PLC uses the corresponding A/D and D/A conversion module and a variety of control algorithms to deal with the analog program, to complete the closed-loop control. PID regulation is a general closed-loop control system used more than a regulation method. PID regulation is a kind of regulation method used in general closed-loop control system. Process control in metallurgy, chemical industry, heat treatment, boiler control and other occasions have a very wide range of applications.
3. Motion control
Programmable controllers can be used for circular or linear motion control. Generally use a special motion control module, such as can drive a stepper motor or servo motor single-axis or multi-axis position control module, widely used in a variety of machinery, machine tools, robots, elevators and other occasions.
4. Data processing
Programmable controllers have mathematical operations (including matrix operations, function operations, logic operations), data transfer, data conversion, sorting, table lookup, bit operation and other functions, you can complete the data acquisition, analysis and processing. Data processing is generally used in some large-scale control systems such as paper, metallurgy, food industry.
5. Communication and networking
Programmable controller communication includes communication between programmable controllers and programmable controllers and other intelligent devices. With the development of factory automation network, now the PLC has a communication interface, communication is very convenient.
Programmable controllers are devices that are used for automated control of industrial production, and generally do not need to take any measures to be used directly in an industrial environment. However, despite the high reliability and strong anti-interference ability as mentioned above, when the production environment is too harsh, electromagnetic interference is particularly strong, or improper installation and use, it may cause program errors or arithmetic errors, thus generating erroneous inputs and causing erroneous outputs, which will result in loss of control of the equipment and misuse of the equipment, thus failing to ensure the normal operation of programmable controllers, to improve the control system of programmable controllers To improve the reliability of the programmable controller control system, on the one hand, programmable controller manufacturers to improve the anti-jamming ability of the equipment; on the other hand, the requirements of the design, installation and maintenance of the use of high attention to multi-party cooperation in order to solve the problem of perfect, effective enhancement of the system's anti-jamming performance.
Today's era is an era of automation, traffic light control and other equipment in many industries are closely related to the computer. Therefore, a good traffic light control system will give the road congestion, violation control and other aspects of technical innovation. With the rapid development of large-scale integrated circuits and computer technology, as well as the extensive use of artificial intelligence in control technology, intelligent devices have developed greatly and are the mainstream direction of modern technology development. This paper describes the design of an intelligent traffic light system. The intelligent traffic light control system can achieve the following functions: monitoring four major traffic intersections in an urban area; each intersection has a fixed work cycle, and the central control center can change its cycle when the road is congested; the motor vehicle violating the rules at the intersection can be photographed instantly and the license plate number can be extracted. In the world, a microelectronics technology, computers and communications technology as the guide to information technology and information industry as the center of the information revolution in the ascendant. How to combine computer technology with practical applications more effectively and effectively play its role is the hottest topic in the scientific community, but also today's computer applications in the field of unprecedented activity. This paper is mainly from the application of microcontroller to realize the intelligent management of intersection traffic lights, to control the normal operation of passing vehicles.
With the development of urban and economic, traffic signals play an increasingly large role, because of traffic signals, so that the traffic flow, the flow of people have a standardized, at the same time, reduce the probability of traffic accidents. However, traffic signals are not reasonable to use or set up, will also affect the smooth flow of traffic.
Traffic signals consist of red, green and yellow lights. The red light indicates that traffic is prohibited, the green light indicates that passage is permitted, and the yellow light indicates a warning. Traffic signals are divided into motor vehicle signals, non-motorized signals, pedestrian crosswalk signals, lane signals, directional signals, flash warning signals, road and railroad crossing signals. Traffic signals for road intersections, through the vehicles, pedestrians, issued by the instructions to move or stop, so that the people who arrive at the same time, the vehicle traffic flow to minimize mutual interference, so as to improve the capacity of the intersection, to ensure that the intersection smooth and safe.
Crossroads traffic signal site schematic shown in Figure 1, north-south and east-west each direction has a red, green, yellow three kinds of signals, in order to ensure traffic safety, the requirements are as follows.
1) PLC is used to form the crossroads of the north-south and east-west traffic signal electrical control. After the system is powered on, the traffic command signal control system is controlled by a 3-bit transfer switch SA1. SA1 handle points to the left 45? when the contact SA1-1 connected, the traffic command system began to work in accordance with conventional normal control functions, according to the work sequence shown in Figure 2 week after week, the cycle of work. SA1 handle points to the middle of the 0? when the contact SA1-2 is connected, the traffic command system north-south to SA1 handle points to the right 45? when the contact SA1-3 is connected, the traffic command system east-west green light is always on, north-south red light is always on.
2) normal control
① When the east-west direction allows passage (green light), the north-south direction should be prohibited (red light); Similarly, when the north-south direction allows passage (green light), the east-west direction should be prohibited (red light). ② in the green signal to switch to red signal before, in order to remind drivers to slow down in advance and brake, there should be obvious prompt signal: green light flashes while the yellow light. ③ Signal control system should be able to start the automatic cycle of action.
The timing diagram of the signal lamp action is shown in Figure 2, which is drawn according to the signal lamp set 1 and set 0 two states, set 1 that the signal lamp is lit.
3) input/output signal distribution
With the rapid development of microprocessors, network communications, human-machine interface technology, industrial automation technology is changing day by day, a variety of products are highly competitive, and new products continue to emerge. PLC is also by the initial can only deal with switching and the development of the analog and data can be dealt with, coupled with the DCS, pid regulator, industrial pc and other technologies, so that it is no longer a simple control device, and will certainly be with the continuous development of automatic control technology and development and survival. Programmable controllers in industrial automation control, especially the position of sequential control, in the foreseeable future, can not be replaced.
plc graduation design thesis IIPLC engineering application analysis
Abstract: The article for the PLC engineering application development process of the use of the characteristics of the PLC hardware composition, software structure, analyzes the PLC control use of the work process, and finally discusses the PLC programming language statements, the application of PLC in the control system has a certain significance of guidance.
Keywords: PLC engineering; hardware system; software system; programming language statements; control system Literature identification code: A
CCTS: TP27 Article number: 1009-2374(2015)34-0033-03 DOI: 10.13535/j.cnki.11-4406/n.2015. 34.017
Programmable Logical Controller (PLC) is a new type of industrial automation device, and the core of PLC is microprocessor, which is a fusion of automation, communication, and computer technologies.PLC is characterized by simple and flexible programmability, ability to withstand the harsh working environment PLC is characterized by simple and flexible programmability, high resistance to harsh operating environments, and strong adaptability. PLC is widely used in industrial control by virtue of its small size, low price, light weight, and other advantages, and is increasingly widely used in the automation of thermal power plant engineering.
1 PLC structure study
Different models of programmable logic controller structure and composition of the same basic principles, the study of the principle of programmable control should start from the hardware structure and software development.
1.1 Hardware components of the PLC
The hardware system components of the PLC include the CPU board, input and output circuits, memory expansion interfaces and so on.
1.1.1 CPU board: the core system of the PLC is the CPU board, the CPU board contains the central processor, read-only memory, random memory, parallel and serial interfaces, and other components. CPU board in the PLC is the role of the operation and control program, the different logic operations, arithmetic operations, and the system as a whole play a role in managing and controlling the components. Random memory and read-only memory are equipped inside the PLC program, with the role of storing various system programs. Parallel and serial interfaces realize the exchange of information between the central processor and each interface circuit.
1.1.2 Input/Output Circuits: Input circuits include both DC input and AC input circuits. The input circuit is able to receive the control signal program prompted by the field input device, and after receiving, the photocoupler can isolate the control signal for program coding, so as to convert it into the standard signal format used in the PLC program, and then through the CPU to realize the signal reading, so as to transfer it to the memory.
Output circuit in the PLC, the main role is to achieve the output signal, the control signal output in the PLC system, the output circuit is responsible for the control signal to other external output devices to achieve the output circuit work. The form of the output circuit is divided into three types: (1) relay form of the output circuit, the form of the output circuit to control the coil of the relay, so that the contacts of the relay on and off, so as to achieve the purpose of electrical isolation; (2) transistor output type circuit, the circuit uses optoelectronic coupler to achieve circuit switching transistor on and off to achieve the purpose of the output device to control; (3) thyristor output (3) Thyristor output type, the thyristor as a medium for the control of the output device, when triggered by the thyristor, the circuit can appear on and off.
1.1.3 Memory expansion interface: read-only memory and random memory used to expand the card box. Expansion of the card box commonly used in three types: (1) COMS ROM, COMS can be provided by the lithium battery on the motherboard backup power, the advantages of the card box is to ensure that the data and program will not be lost in a power outage or blackout failure; (2) erasable programmable ROM card box, the card box needs to use a special programmer in writing, in order to debug the ROM information within the written in the erasure, the internal chip visible through ultraviolet light, the card box can be used in a variety of applications. Through ultraviolet radiation visible internal chip, thus erasing the data within it, and in writing, need to have a certain programming voltage, can be repeated to erase and programming; (3) EEPROM cartridge, electrically erasable programmable read-only memory, is a kind of power outage will not occur in the event of data loss, the implementation of the programming and erasure operations can be realized by using a dedicated programmer.
1.1.4 Input/Output Expansion Interfaces: The CPU and the input and output expansion interfaces are connected through a bus connection method, which can be connected to all the expansion units, thus allowing the signal point scale to have greater flexibility. Input/output expansion interface can also be connected with analog, high-speed pulse and other adapters to expand and enhance the role of the PLC.
1.1.5 Programmer and its interface: The role of the programmer in the PLC is to debug, edit, and test the security of the data and information input. The PLC under normal operation does not need a programmer to program data, so the programmer exists as an independent design of PLC components.PLC is usually equipped with a special interface for the programmer, which is adapted to connect to different types of programmers, in order to complete the writing and debugging of the PLC program.
1.2 Research and Analysis of Programmable Controls
A control system must have a control program in order to realize its control functions. Control programs are divided into the following two types:
1.2.1 Fixed wiring program control. In the old mode of the relay, if you want to control a variety of programs, the circuit connection of the relay needs to be in the form of wiring, the role of the input device is to send control signals into the control system, such as pushbutton switches, sensors, etc.. The role of the output device is to control the action of the controlled person. The way the device controls the output control signal is done by wiring. After the wiring is completed, the control program is also determined, and if the control program needs to be changed again, the entire wiring of the original control program needs to be rewired and connected to develop a new connection. In the complex control system, this type of program control is more difficult, programming feasibility is not high.
1.2.2 Programmable control. Programmable control of the system control, only the use of special programmers, through the corresponding programming language to achieve programming, the control program down to the memory, and finally with the help of programmable controllers on the programming of the implementation of various operations. If you want to change the programmable system, you only need to change the program language in the program memory, which can be done through the programmer without changing the circuit connection and rewiring. Commonly known as the use of specific software programming language to write program code to achieve a variety of controlled objects of action control.
2 PLC engineering principle
PLC core electronic components are microprocessors, can also be regarded as a combination of relays, timers, state devices, etc. PLC, the input relay through the external switch to drive, the output relay is installed with a number of contacts. PLC to carry out the work, in fact, is the implementation of the program. PLC in the working state, the CPU to time-sharing operation as the work. In the working state of PLC, the CPU works on the principle of time-sharing operation and performs the corresponding operation in one cycle, i.e., the program scanning of the CPU. the CPU is very fast in the operation and processing of the program, so the data result from the macroscopic point of view can be found that the program operation of the CPU seems to be completed in a very short period of time. the PLC's process of executing the program is divided into the following three parts:
2.1 Input Processing The PLC uses repetitions of the input relay in the process of executing the program. In the process of executing the program, repeat scanning is applied to complete. Before execution, the CPU programs all input signals into the input memory in the order of the codes appearing in the address, and then begins to carry out program execution. When the CPU executes the program, even if the input state changes, the data content in the input register does not change with the change of the input state until the end of the scanning cycle when the CPU re-reads the input state.
2.2 Program Execution
When the PLC executes a program, it scans the user program according to the sequence. Upon completion of the execution of a program, the required information will be read out by the program through the registers and participate in the program operation, and then the data results of program execution will be programmed into the relevant registers.
2.3 Output Processing
When the PLC has finished executing all the instructions in full, the PLC will input all the program results into the output latching registers, which will eventually be transferred to the program execution terminal.
3 PLC software system components
A complete PLC control system consists of a hardware system and software, the combination of which constitutes a complex control function. In the PLC software system, divided into system programs and user programs.
The role of the system program in the PLC is to manage, serve and translate the user program, which can be regarded as a software platform. The quality of the system program and the performance of the PLC has a direct link to the quality of the system program, the performance of the PLC is strong, and vice versa, the performance is weak. The system software is fixed in the program and cannot be modified or accessed by itself. The user program is the application program, is the user according to the requirements of the control system using the programming language for the preparation of the application, which is stored in the system program specified in the storage location.
4 PLC programming language
The use of sequence-oriented and process-oriented control of the program? Natural language? , that is, the PLC programming language, PLC programming language there are many, such as ladder diagrams, logic equations, language name tables or Boolean algebra and other types of language. The following is an introduction to the commonly used PLC programming language.
The basic PLC instructions (e.g., Mitsubishi FX2 series as an example) are shown below:
4.1 Logic Linkage and Output (LD/LDI/OUT) Instruction
The LD/LDI instruction is used to take a normally open contact/normally closed contact connected to the bus. In addition, at the beginning of the branch, these instructions are used in combination with the ANB (block and) instructions described later; the OUT instructions are used to drive the coils of output relays, auxiliary relays, status devices, timers, and counters, but cannot be used to drive the coils of input relays. For the coils of timers and counters, appropriate constants must be set after the output instruction (OUT).
4.2 Series connection of contacts
AND (and), ANI (not) instruction, AND is a series connection of normally open contacts, ANI is a series connection of normally closed contacts, AND and ANI can be used to make series connection of contacts, while operating in logic. There is no limit to the number of contacts in series, and it is a reusable program instruction.
4.3 Parallel contact instruction
OR (or), ORI (or not) instruction, OR normally open contacts are connected in parallel, ORI normally closed contacts are connected in parallel, both can be used for parallel connection of contacts or used in logic. There is no limit to the number of parallel contacts that can be set, and it is a program instruction that can be reused. When more than two contacts of the series circuit block for parallel connection, should use the latter ORB (block or) instruction.
4.4 Parallel Instruction (ORB) Blocks for Series Circuit Blocks
A series circuit block is a series connection of more than two contact circuits, and in general, a series circuit block is a line branch. When implementing the parallel connection form for series circuit blocks, the LD or LDI instruction is used at the beginning of each branch, and the ORB instruction is used at the end of the branch. In multiple parallel circuits, if the ORB instruction is used at the end of each series circuit block, the number of parallel series circuit blocks is not limited.The ORB instruction is a stand-alone instruction without an operating element number, as is the ANB instruction described later.
4.5 Series Instructions for Parallel Circuit Blocks
ANB (Block and) Series Connection of Parallel Circuit Blocks A circuit in which two or more contacts are connected in parallel is called a parallel circuit block, and each parallel circuit block is usually called a branch. When making series connections of parallel circuit blocks, the LD or LDI instruction is used at the beginning of each branch, and the ANB instruction is used at the end of the parallel circuit block to realize a series connection with the previous circuit.
The ANB instruction, like the aforementioned ORB instruction, is a stand-alone instruction with no operating element number. If multiple parallel circuit blocks are connected in series with the preceding circuit in sequence, there is no limit to the number of ANB instructions that can be used.
4.6 Master Contact Instructions
MC (master), MCR (master reset), MC master circuit block start, MCR master circuit block end.
In the programming process, it is often encountered that several logic rows are controlled by a contact or a group of contacts at the same time, controlled by a public **** condition called master control, which can then be edited using the MC/MCR instruction. When the master control condition is satisfied, the instruction between MC and MCR is executed. The execution of the MC instruction moves the bus after the MC master control contact, and the execution of the MCR instruction returns the bus to its original position.The MC and MCR instructions must be used in pairs.
4.7 Set and Reset Instructions
SET (reset), RST (reset), SET makes the component self-hold ON, makes the component self-hold OFF, and clears the data register. When the SET instruction is executed, the corresponding operating elements (Y, M, S) are set and have a self-hold function. When the RST instruction is executed, the corresponding operation element (Y, M, S) is set and has a self-hold function. The data register D, variable address register V and Z can also be cleared to zero using the RST instruction.
4.8 END (End of Program) Instruction
The END input/output handler returns to step ?0?.
5 Conclusion
When designing with a PLC system, a large number of input points are required. Especially for thermal power plant systems that require multiple locations and multiple points of control, the number of input points required is more prominent. Therefore, it is possible to effectively reduce the number of input points of the system and effectively reduce the cost of the PLC. In the design of PLC control system, it is required to use the following skills and points: (1) in the design, according to the different control functions of the software to design accordingly, if it is a ladder diagram, the design should be in the form of modularization; (2) in the use of cyclic scanning, the timing relationship between the instruction and the instruction, the module and the module should be kept unchanged, so that the program will run normally on the basis of the design function; (3) For the parameter items that need to be adjusted such as automatic door closing, speed change, and automatic switching time, make them separate from the program. Therefore, when it is necessary to adjust the parameters, there is no need to change the program, which is convenient, quick and easy to debug, and at the same time, it can make the reliability of the software improve effectively; (4) For the series switch and linkage switch, such as the interlocking switches between the storey doors, the roof of the car and the car, it can be set up as a single input point; (5) For the switching signals having the same function, such as the switching of the safety contact plate and the gate switch, it can be input in the form of parallel linkage. It can be input into PLC in the form of parallel connection; (6) Use the combined button input method, the application of which should use two input points to combine the button keys, and then the program automatically identifies and recovers the combined signals; (7) Inputs for coding: Using binary coding, the identification signals are input into the button switches, and then automatically transferred to the PLC program for recovery and identification, which can be very Effectively reduce the number of PLC input points.
References
[1] Zhu Shanjun, et al. Programmable Control System Principles, Applications, and Maintenance [M]. Beijing: Tsinghua University Press, 1992.
[2] Wang Zhaoyi. Programmable controller tutorial [M]. Beijing: Machinery Industry Press, 2000.
Author's introduction: Wang Qiong (1980-), male, Zhejiang Shengzhou, Shangyu Hangxie Cogeneration Co., Ltd. thermal control engineer, research direction: power plant automation control system management and maintenance, routine maintenance of hardware and software programming.