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  1. 1. CHAPTER 1 INTRODUCTION1.1 GENERAL Simplification of engineering and precise control of manufacturing process can result in significant cost savings. The most cost-effective way, which can pay big dividends in the long run, is flexible automation; a planned approach towards integrated control systems. It requires a conscious effort on the part of plant managers to identify areas where automation can result in better deployment/utilization of human resources and savings in man-hours, down time. Automation need not be high ended and too sophisticated; it is the phased, step- by-step effort to automate, employing control systems tailored to one‟s specific requirements that achieves the most attractive results. That is where Industrial electronics has been a breakthrough in the field of automation and control techniques.1.2 ROLE OF ELECTRONICS IN AUTOMATION A constant demand for better and more efficient manufacturing and processmachinery has led to the requirement for higher quality and reliability in control techniques.With the availability of intelligent, compact solid state electronic devices, it has been possibleto provide control systems that can reduce maintenance, down time and improve productivityto a great extend. By installing efficient and user friendly industrial electronics systems formanufacturing machinery or processors, one can obtain a precise, reliable and prolific meansfor generating quality products. Considering the varied demand and increasing competition,one has to provide for flexible manufacturing process. One of the latest techniques in solidstate controls that offers flexible and efficient operation to the user is “PROGRAMMABLECONTROLLERS”. The basic idea behind these programmable controllers was to providemeans to eliminate high cost associated with inflexible, conventional relay controlledsystems. Programmable controllers offer a system with computer flexibility: 1.Suited to withstand the industrial environment 2.Has simplicity of operation 1
  2. 2. 3.Maintenance by plant technicians and 4.Reduce machine down time and provide expandability for future.1.3 OBJECTIVES OF THE WORK 1. To study the plc. 2. To understand the lift management system using ladder diagram and variouslimitations.1.4 ORGANISATION OF THE THESIS This thesis consists of five chapters including introduction as the first chapter. In chapter 2 to understand the plc architecture. In chapter 3 deals with plc programming. Chapter 4 deals with hardware design. Chapter 5 contain results and conclusion. 2
  3. 3. CHAPTER 22.1 INTRODUCTION A Programmable controller is a solid state user programmable control system withfunctions to control logic, sequencing, timing, arithmetic data manipulation and countingcapabilities. It can be viewed as an industrial computer that has a central processor unit,memory, input output interface and a programming device. The central processing unitprovides the intelligence of the controller. It accepts data, status information from varioussensing devices like limit switches, proximity switches, executes the user control programstore in the memory and gives appropriate output commands to devices like solenoid valves,switches etc. Input output interface is the communication link between field devices and thecontrollers; field devices are wired to the I/O interfaces. Through these interfaces theprocessor can sense and measure physical quantities regarding a machine or process, such as,proximity, position, motion, level, temperature, pressure, etc. Based on status sensed, theCPU issues command to output devices such as valves, motors, alarms, etc. Programmer unitprovides the man machine interface. It is used to enter the application program, which oftenuses a simple user-friendly logic.2.2 PLC ARCHITECTURE PLCs contain three basic sections: 1. Central processing unit (CPU). 2. Memory: EPROM, RAM, and so on. 3. Input/output section for communication with peripherals (ADC, DAC). 3
  5. 5. A PLC is basically a black box with a number of inputs from, and a number ofoutputs is shown in Figure 2.2. It can make decisions, store data, do timing cycles, do simplearithmetic, convert codes, and so on. The basic difference between this black box and ahardware logic system using IC chips or a relay controlled system, is that specific codedmessages are stored in areas called program memory, which are PROM or ROM and RAMchips. It is, however, much easier to change a program when a different process is requiredthan to rewire the control system. For example, it may take electricians a couple of weeks to require a pipe mill,whereas a programmer will spend only a fraction of this time to reprogram a PLC since nowires will have to be changed. In addition, various recipes can be stored in memory andaccessed when required, making the program extremely flexible. The system operatesthrough interaction with the processor and program memory. When the power to the systemis turned on, the processor reads the first instruction stored in memory and acts on thisinstruction. When completed, it goes back to the memory for the next instruction, and so onuntil task is complete. This operation is called the fetch-execute cycle. The processorcommunicates with the outside world via input and output modules.2.3 PROCESSOR MEMORY ORGANIZATION The memory of a PLC is organized by types.The memory space can be divided into two broad categories: Program and Data Memory: Advanced ladder logic functins allow controllers to perform calculatins, make decisions and do other complex tasks. Timers and counters are examples of ladder logic functions. They are more comples than basic inputs contacts and output coils and relay heavily upon data stored in the memory of the PLC. 2.3.1 PROGRAM FILES: 5
  6. 6. FIGURE 2.3 PROGRAM FILES The user program will account for most of the memory of a PLC system.Program filescontain the logic controlling machine operation.This logic consistes of instructions that areprogrammed in a ladder logic format. A particular portion of the processor‟s memory is used for storing the user programinstructions. We will use the name user program memory to refer to this processorsubsection. Before a PLC can begin controlling an industrial system, a human user must enterthe coded instructions that make up the user program. This procedure called programming thePLC. As the user enters instructions, they are automatically stored at sequential locationswithin the user program memory. This sequential placement of program instructions is self-regulated by the PLC, with no discretion needed by the human user. The total number ofinstructions in the user program can range from a half dozen or so, for controlling a simplemachine, to several thousand, for controlling a complex machine or process. After theprogramming procedure is complete, the human user manually switches the PLC out toPROGRAM mode into RUN mode, which causes the CPU to start executing the programfrom beginning to end repeatedly.2.3.2 DATA FILES: FIGURE 2.4 DATA FILES The data file protion of memory stores input and output status, processorstatus, the status of various bits and numerical data. A PLC is a computer, after all. Therefore,it can perform arithmetic, numeric comparisons, counting, etc. Naturally the numbers anddata can change from one scan cycle to the next. Therefore the PLC must have a section of itsmemory set aside for keeping track of variable data, or numbers, that are involved with theuser program. This section of memory we will call data memory. When the CPU is executing 6
  7. 7. an instruction for which a certain data value must be known, that data value is brought infrom data memory. When the CPU executes an instruction that provides a numerical result,that result is put out into data memory. Thus, CPU can read from or write to the datamemory. Understand that this relationship is different from the relationship between the CPUand the user program memory. When the user program is executing, the CPU can only readsfrom the user program memory, never write to it.2.3.3 INPUT TABLE FILE OPERATION: FIGURE 2.5 INPUT IMAGE TABLE Processor continually reads current input status and updates input image tablefile. The input conditions are stored in the input image table, which is a portion of theprocessor‟s memory. That is, every single input module in the I/O section has assigned to it aparticular location within the input image table. That particular location is dedicated solely tothe task of keeping track of the latest condition of its input terminal. As mentioned in earliersection, if the input terminal has 5v dc power fed to it by its input device, the location withinthe input image table contains a binary 1(HI); if the input terminal has no 5v dc power fed toit, the location contains a binary 0(LO). The processor needs to know the latest inputconditions because the user program instructions are contingent upon those conditions. Inother words, an individual instruction may have one outcome if a particular input is HI and adifferent outcome if that input is LO. 7
  8. 8. 2.3.4 OUTPUT TABLE FILE OPERATION: FIGURE 2.6 OUTPUT IMAGE TABLE Processor continually activates or deactivates ouput status according to outputimage table file status. The output conditions are stored in the output image table, which isanother portion of the processor‟s memory. The output image table bears the same relation tothe output interface of the I/O section that while terminals are analog inputs. You can directlyconnect any analog input to the processor via these terminals. Analog signal from theseterminals is first converted to digital value via programmable peripheral interface (PPI). TheI/O section‟s output modules are functionally the same as the output amplifiers. They receivea low power digital signal from the processor and convert it into a high power signal capableof driving an industrial load. A modern PLC output module is optically isolated, and uses atriac, power transistor or relay as the series connected load controlling device. Terminal 1 to8 are these type of O/P terminals whereas terminal D/A is Analog output terminal fromprocessor. Each output device is wired to a particular output terminal on the I/O interface.Thus, for example, if output module 1 receives a digital 1 by applying 5v dc to outputterminal 1, thereby illuminating LED is extinguished. Besides 5v dc (TTL devices), I/Omodule are also for interfacing to other industrial levels, including 12v dc. The input image table bears to the input modules. That is, every single output modulehas assigned to it a particular memory location is dedicated solely to the task of keeping trackof the latest condition of its output module. Of course, the output situation differs from theinput situation with regard to the direction of information flow is from the output image tableto the output modules, while in the input situation the information flow is from the input 8
  9. 9. modules to the input image table. The locations within the input and output image tables areidentified by addresses, which refers to unique address of each terminal.2.4 The Processor: The processor of a PLC holds and executes the user program. In order to carry out thisjob, the processor must store the most up-to-date input and output conditions.2.5Central processing unit: The subsection of the processor that actually performs the program execution will becalled the central processing unit (CPU) with reference to input and output image table CPUexecutes the user program and continuously updates the output image table. The output imagetable has a dual nature; its first function is to receive immediate information from the CPUand pass if on to the output modules of the I/O section; but secondly, it also must be capableof passing output information “backward” to the CPU, when the user program instruction thatthe CPU is working on calls for an item of output information. The input image table does nothave its dual nature. Its single mission is to acquire information from the input modules andpass that information “forward” to the CPU when the instruction that the CPU is working oncalls for an item of input information.2.6The complete scan cycle: As long as the PLC is left in the RUN mode, the processor executes the user programover and over again. Figure depicts the entire repetitive series of events. Beginning at the topof the circle representing the scan cycle, the first operation is the input scan. During the input scan, the current status of every input module is stored in the inputimage table, bringing it up to date. Following the input scan, the processor enters its userprogram execution. Sometimes called “program scan”. The program executes with referenceto input and output image tables and updates output image table. Throughout the userprogram execution, the processor continuously keeps its output image table up to date, asstated earlier. However, the output modules themselves are not kept continuously up to date.Instead, the entire output image table is transferred to the output module during the outputscan following the program execution. 9
  10. 10. 2.7Operating System of PLC: The function of the operating system is to present the user with the equivalent of anextended machine or virtual machine that is easier to program than the underlying hardware.Due to this operating system, PLC is very easy to program. It can be programmed usingelectrical schemes with familiar relay symbols so that a plant electrician can easily access thePLC. Even though he does not know the assembly language or even if he may not have anyfamiliarity with computers and electronics, he will be able to program the PLC. The functionof PLC Operating system is: 1. Loads the user program from programming device to program memory. 2. To read status of input devices. 3. To execute user program. 4. To form and update input image table. 5. As per the status of output image table controls the output devices. 6. To provide user-friendly functions.This O.S. makes supervision over entire system, so O.S. programs are said to running insupervisory mode. When the user completely enters his program in user memory, he transferscontrol from PROGRASM mode to RUN mode. In RUN mode the control of the wholesystem is transferred to operating system. Now operating system takes care of the wholesystem such that the whole system becomes automatic and appears as magic to users.2.8BENEFITS OF PROGRAMMABLE CONTROLLERS: 1. Programmable controllers are made of solid state components and hence providehigh reliability.2.They are flexible and changes in sequence of operation can easily be incorporated due toprogrammability. They may be modular in nature and thus expandability and easy installationis possible. 10
  11. 11. 3.Use of PLC results in appreciable savings in Hardware and wiring cost. 4.They are compact and occupy less space. 5.Eliminate hardware items like Timers, counters and Auxiliary relays. The presence for timers and counters has easy accessibility. 6.PLC can control a variety of devices and eliminates the need for customized controls. 7.Easy diagnostic facilities are provided as a part of the system. Diagnosis of theexternal systems also becomes very simple. Thus easy service/maintenance. 8.Programming devices provide operator friendly interface with the machine. Beingan outcome of the latest art of electronics technology, Programmable controllers providehigher level of performance with computers is possible. Useful management data can beobtained and maintained. 9.It has total protections against obsolescence and has wide scope for upgradation.2.9 CONCLUSION: The basics operation of programmable logic controller and purpose of programmablelogic controller.And the benfit of plc . 11
  12. 12. CHAPTER 3 PLC PROGRAMMING3.1 INTRODUCTION The basic need or purpose of writing a PLC program is the same for all PLCs.However various PLC manufacturers follow their own programming method and givedifferent name for the method. The detailed programming method or procedures are availablein manufacturer‟s manuals. Mostly the task or what action or functions to be carried out arefirst formulated as a circuit. Then functions are simply converted from the diagram into aprogram in one of the method.3.2 METHODS OF PLC The methods used by popular siemens group a well known PLC in India fall underthree kinds 3.2.1 Logic ladder diagram method. 3.2.2 Control system flowchart method (CSF). 3.2.3 Statement list method (STL). the basic symbols used in ladder diagram method. Normally opened Normally closed FIGURE 3.1 NORMALLY OPEN CONTACT FIGUER 3.2 NORMALLY CLOSED CONTACT 12
  13. 13. FIGURE 3.3 Output (or) Coil FIGURE 3.4 INPUT AND OUTPUT COIL3.2.1 Logic ladder diagram method: In ladder diagram, the power source is representing by two vertical rail of ladder andthe various control circuit make up the rung. Normally open contacts of a switch or relay arerepresented by two parallel vertical lines. Normally closed contacts are symbolized byparallel vertical lines with a diagonal. Simple ladder diagrams with two inputs are drawnbelow3.2.1.1 Simple example Ladder diagram Ladder diagrams are specialized schematics commonly used to document industrialcontrol logic systems. They are called "ladder" diagrams because they resemble a ladder, withtwo vertical rails (supply power) and as many "rungs" (horizontal lines) as there are controlcircuits to represent. If we wanted to draw a simple ladder diagram showing a lamp that iscontrolled by a hand switch, it would look like this: 13
  14. 14. FIGURE 3.5 EXAMPLE FOR LADDER DIAGRAM The "L1" and "L2" designations refer to the two poles of a 120 VAC supply, unlessotherwise noted. L1 is the "hot" conductor, and L2 is the grounded ("neutral") conductor.These designations have nothing to do with inductors, just to make things confusing. Theactual transformer or generator supplying power to this circuit is omitted for simplicity3.2.2 Control system flowchart method (CSF): Control system flowchart method (CSF) is a graphical representation method. In thisthe control task is marked using symbols defined by DIN40700 AND 40719 standardnumbers. The inputs are placed in the left side of the symbol and output is placed in the rightof symbol. For the control task we draw the control system flow chart and its equivalentladder diagram. Flow chart ladder diagram I:0/1AI01 O:4/1&AI02 = I:0/2O41 Here A, =, Oetc.., are the control statement. A represent AND operation, = represent result or assignoperation. The remaining parts are the operand which contains the identifier and parametersor address.3.2.3Statement list method (STL): It uses mnemonic to formulate or represent the control task. Finally the program isalways stored in the statement list (MC5 machine language) in program memory of computer.That is, the programmer automatically converts the program into STL from the Controlsystem flowchart method (CSF) or logic ladder before transferring it to computer. The task issubdivided into individual control statements for execution by the PLC.A control statement isthe smallest indivisible unit of program. It acts as an instruction for the processor andcorresponds to the STL format.3.3CONCLUSION: This chapter consists of Logic diagram ladder method, control system flow chartmethod(CSF) and statement list methods were used 14
  15. 15. CHAPTER 4 HARDWARE DESIGN4.1 INTRODUCTION: The objective of the project is the design and implementation of a three-level elevatorsystem controlled by a Programmable Logic Controller (PLC). The design was limited tothree levels due to the limited number of inputs provided by the AB PLC available. Somesuggestions are given later as to how to extend the elevator system to more than three levels.Moreover, the design was not based on a first-come first-served basis, since this approachwas not found to be practical. As a practical compromise between energy consumption andspeed of response, we decided to combine all requests going in one direction (up or down),and then process them in sequential order. This was achieved in the following manner: if theelevator is going up, all „up‟ requests are given higher priority than the „down‟ requests untilthe elevator reaches the last destination upwards. Then the elevator goes down but now givespriority to all „down‟ requests over the „up‟ ones. More details on this will given in thesection „Software design‟.4.2 Hardware design: 15
  16. 16. The objective of the hardware design is to develop the interface circuit between thePLC and the elevator system and the elevator control panel, with both external and internalrequests. These requests are produced by push buttons that send continuous signals to thePLC when activated. Each push button is connected to an LED to identify the request placed.In addition, the four floors are represented by three LEDs, one for each level. Furthermore, analarm switch is installed to produce a flashing signal whenever activated. This facility wasintroduced to simulate the desire for a sudden stoppage of the elevator either for reasons ofsafety or for requests for a repair job to be carried out on the elevator. In order to obtain thedesired setup, we needed to find a way to capture the pulse generated by a depressed pushbutton. We also needed to make sure that the PLC is recognizing these signals in order for itto correctly perform the required action. As explained below, both issues were resolved byusing set/reset flip flops and relays respectively. The block diagram of the system‟s layout isshown in Fig. 1, where both the interface between the PLC and the elevator system with thecontrol panel are drawn.4.3Description of the interface circuit:The hardware components used in the project are listed below: Ab 1400, SR flip flops andbuffers, respectively. Voltage supply. Push buttons, LEDs, resistors, relays, a switch, andconnecting wires. Since the number of required inputs and outputs, i.e. 12 and 8 respectively,matches the maximum input/output capability of the PLC used, there is no need for anymultiplexing or demultiplexing operations. Thus all inputs and outputs used can be directlycontrolled by the PLC. the push buttons were connected to the SR flip flops, since the PLCneeds continuous signals to process, and so do the lights that indicate the requests placed. Theflip flop holds the signal until the reset is activated. The reset of the flip flop is the levelposition for levels L1 and L4. So when the elevator reaches one of these two levels and arequest is placed the output will reset the requested signal. However levels L2 and L3 arereset by software. The reason for that is because L2 and L3 are intermediate levels. So whenthe elevator is travelling upwards or downwards, it has to either flash at the level it passes toshow the current elevator position or service this level if its request has the appropriatedirection by setting its request. In this case, it will also reset all requests associated with theserviced levels. 16
  17. 17. 17
  18. 18. 18
  19. 19. FIG 3.2 PLC based Lift management system Ladder Diagram 19
  20. 20. Description of the control panel: The 12 inputs and 8 outputs used in this project arelisted and defined in Table 1. As shown in Fig. 3, the elevator system consists of threesections: internal requests, external requests, and the elevator position. The internal requestsare represented by the push buttons inside the elevator which consists of three push buttons(1–4) and a door open (DO) push button. A door close push button could not have beenincluded in the design because of the limited number of available inputs. The externalrequests are represented by the six push buttons located outside the elevator and distributedaccording to their corresponding floors. It consists of six push buttons distributed accordingto the position of the level. The elevator position is displayed by the three LEDs, one for eachlevel, which are directly controlled by the PLC according to the location of the elevator.4.4 APPLICATIONS OF PLC: In the present industrial world, a flexible system that can be controlled by user at siteis preferred. Systems, whose logic can be modified but still, used without disturbing itsconnection to external world, is achieved by PLC. Utilizing the industrial sensors such aslimit switches, ON-OFF switches, timer contact, counter contact etc., PLC controls the totalsystem. The drive to the solenoid valves, motors, indicators, enunciators, etc are controlledby the PLCs. The above said controlling elements (normally called as inputs of PLCs) andcontrolled elements (called as outputs of PLCs) exist abundantly in any industry. Theseinputs, outputs, timers, counters, auxiliary contacts are integral parts of all industries. Assuch, it is difficult to define where a PLC cannot be used.Proper application of a PLC begins with conversion of information into convenientparameters to save money, time and effort and hence easy operation in plants andlaboratories. The areas where PLC is used maximum are as follows: 20
  21. 21. 1. The batch processes in chemical, cement, food and paper industries which are sequential in nature, requiring time of event based decisions is controlled by PLCs.2. In large process plants PLCs are being increasingly used for automatic start up and shut down of critical equipment. A PLC ensures that equipment cannot be started unless all the permissive conditions for safe start have seen established. It also monitors the conditions necessary for safe running of the equipment and trips the equipment whenever any abnormality in the system is detected.3. The PLC can be programmed to function as an energy management system for boiler control for maximum efficiency and safety.4. In automation of blender reclaimers5. In automation of bulk material handling system at ports.6. In automation for a ship unloader.7. Automation for wagon loaders.8. For blast furnace charging controls in steel plants.9. In automation of brick moulding press in refractories.10. In automation for galvanizing unit.11. For chemical plants process control automation.12. In automation of a rock phosphate drying and grinding system.13. Modernization of boiler and turbogenerator set.14. Process visualization for mining application. 21
  22. 22. 15. Criteria display system for power station. 16. As stored programmed automation unit for the operation of diesel generator sets. 17. In Dairy automation and food processing. 18. For a highly modernized pulp paper factory. 19. In automation system for the printing industry. 20. In automation of container transfer crane. 21. In automation of High-speed elevators. 22. In plastic moulding process. 23. In automation of machine tools and transfer lines. 24. In Mixing operations and automation of packaging plants. 25. In compressed air plants and gas handling plants. 26. In fuel oil processing plants and water classification plants. 27. To control the conveyor/classifying system. Thus PLC is ideal for application where plant machine interlock requirements arefinalized at a later stage and need changes during engineering trial runs, commissioning ornormal use. It can be used extensively to replace conventional relay controls in powerstations, refineries, cement, steel, fertilizer, petrochemical, chemical industries etc.Applications can thus be extended from monitoring to supervision, control and management. 22
  23. 23. 4.5 CONCLUSION: 23
  24. 24. CHAPTER 5 RESULT AND CONCLUSION5.1 RESULTS Based on the user preferred floor request the lift car has been successfullyoperated by using the programmable logic controller the program is very reluctant thegreater response time has been achieved from the controller.5.2 CONCLUSION Basically every lift car has been controlled by the microcontroller if that anyproblem occurs it is difficult to find the problem, so we are using the plc controller in thisprocess we can easily find out the problem through Programmable Logic Controller. Both in input and output the response time is greater than compared with otherdigital controller since the durability, reliability and sustainability is higher. 24