Beginner guide (986746), страница 3
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1.4Fig. 1.4: Typical Conventional Control PanelqDisadvantage of Conventional Control PanelIn this panel we can observe the following pointsThere are too many wiring work in the panel.Modification can be quite difficult.Troubleshooting can be quite troublesome as you may require a skillful person.Power consumption can be quite high as the coil consumes power.Machine downtime is usually long when problems occur, as it takes a longer time to troubleshootthe control panel.• Drawings are not updated over the years due to changes. It causes longer downtime in maintenanceand modification.•••••1-81.qINTRODUCTIONProgrammable Controller Control Panel and Their AdvantagesWith the arrival of programmable controllers, the control design and concept improve tremendously.There are many advantages in using the programmable controllers.A typical example of the PLC control panel is shown in Fig 1.5.Fig.
1.5: Typical PLC Control PanelqAdvantages of PLC Control Panel••••••••••Here are the major advantages that can be distinguishably realized.The wiring of the system usually reduces by 80% compared to conventional relay controlsystem.The power consumption is greatly reduced as PLC consume much less power.The PLC self diagnostic functions enable easy and fast troubleshooting of the system.Modification of control sequence or application can easily be done by programming throughthe console or computer software without changing of I/O wiring, if no additional Input orOutput devices are required.In PLC System spare parts for relays and hardware timers are greatly reduced as compared toconventional control panel.The machine cycle time is improved tremendously due to the speed of PLC operation is amatter of milliseconds.
Thus, productivity increases.It cost much less compared to conventional system in situation when the number of I/Os is verylarge and control functions are complex.The reliability of the PLC is higher than the mechanical relays and timers.An immediate printout of the PLC program can be done in minutes. Therefore, hardcopy ofdocumentation can be easily maintained.1-91.qINTRODUCTIONConversion of Conventional Control Circuit to PLCExample 1: Starting and Stopping of a 3-phase motor.ThRUYVMotor (1.5 kw)WBCircuitBreakerMgNPB1PB2EMgStart Push -buttonIStartPush-buttonTHMgFig. 1.5When the push-button PB1 is pressed, current I will flow through the circuit and energize magneticcontact Mg which in turn closes the Mg contacts. The contact Mg parallel the push-button PB1 isfor self-holding so that PB1 can be released.
The other Mg contacts closes to switch on the 3-pbasemotor.To connect the above circuit in a PLC system to PLC wiring circuit, we need to identify the inputand output devices. The input devices are start push-button (PB1) and stop push-button (PB2) andthe output device in this case is only one magnetic contactor that controls the 3-phase motor. Thewiring circuit is shown in Fig. 1.61-101.INTRODUCTIONCircuitBreakerThURMotor (1.5 kw)VYWBMgNFig.
1.6 Motor CircuitStart Push-buttonEPB1Stop Push-buttonAssignmentPB2−Input = Channel 00Output = Channel 10DC24V+FUSECOMINPUTOUTPUTMgThMagnetic ContactorFig. 1.7 Hard Wire Circuit for PLC ConnectionPB1 (0000)PB2 (0001)1000Start PushbuttonStop PushbuttonControlMg1000END (01)Fig. 1.8 Ladder diagramFig. 1.7 shows the wiring circuit of the I/O devices.Fig. 1.8 is the ladder diagram for the conversion. It must be programmed into the PLC.Example 2: Sorting Machine1-111.INTRODUCTIONL(Start)PB11(Stop)PB2NCTR1CR1Begin Cycle 2, 3, 7CR1Conveyor (0.1A) MotorCR12CR13Run LightLS1 (Limit Switch)4CR2SortingCR2Cylinder5LS2 (Limit Switch)6CTR1CounterPB27CRT1End Cycle Bell8Fig.
1.9 Conventional Circuit for Sorting MachineIn this example, you have to determine again the number of input and output devices used for thecontrol circuit. Assign the I/O for the PLC and then wire it according to the actual I/O devices. Thewiring circuit is shown in Fig. 1.10.
The input devices such as PB1 is assign to the input 0, LS1 asinput 1, LS2 as input 2 and PB2 as input 3. The output devices such as conveyor motor is assignedto output 1000, cylinder solenoid as output 1001 and End Cycle Bell as output 1002.1-121.INTRODUCTION+−-DC24VLNLS1LS2PB1PBINPUTOUTPUTConveyorMotorRun LightMTREnd Cycle BellThCylinderSolenoidFig. 1.10 Wiring Circuit of PLC for Sorting MachinePB1PB2000020000003StopCNT12000Begin Cycle20001000Conveyor MotorAnd RUN LightLS1 (Limit Switch)2001000120011001LS2 (Limit Switch)0002PB2Cylinder SolenoidC/PCNT1Rst#10000003CNT11002End Cycle BellEND (01)Fig.
1.11 Ladder Diagram of PLCFig. 1.10 shows the wiring circuit of the I/O devices.Fig. 1.11 is the software ladder diagram to be loaded into the PLC in order for the PLC to runaccording to the sequence of operation.1-131.qINTRODUCTIONA Systematic Approach of Control System Design Using AProgramming Logic ControllerThe concepts of controlling a control system is a very simple and easy task. It involves a systematicapproach by following the operation procedure.1.Determine The Machine Sequence of OperationFirstly, you have to decide what equipment or system you want to control. The ultimate purposeof the programmable controller is to control an external system.
This system to be controlledcan be a machine equipment, or process and is often generically called the controlled system.The movement of the controlled system is constantly monitored by the input devices that give aspecified condition and send a signal to the programmable controller. In response, theprogrammable controller outputs a signal to the external output devices which actually controlsthe movement of the controlled system as specified and thus achieves the extended controlaction. In simplicity, you need to determine the sequence of the operation by drawing out theflowchart.2.Assignment of Inputs and OutputsSecondly, all external input and output devices to be connected to the programmable controllersmust be determined.
The input devices are the various switches, senses, etc. The output devicesare the solenoids, electromagnetic valves, motor, inductors etc.After identifying all the various INPUT and OUTPUT devices, assigned the numberscorresponding to the INPUT and OUTPUT number of the particular programmable controlleryou will be using. The actual wiring will follow the numbers of the programmable controller.The assignment of INPUT and OUTPUT numbers must be carried out before writing the ladderdiagram because the number dictate what is the precise meaning of the contacts in the ladderdiagram.3.Writing of the ProgramNext, write the ladder diagram program by following the control system sequence of operationas determined by step one.4.Programming into MemoryNow, you can apply power to the programmable controller.
Depending on the type ofprogrammable controller, you may have to do a I/O generation to prepare the systemconfiguration. After that, you can enter your program in the memory either by programmingconsole or by computer aided ladder software tool. After completion of the programming, youshould check for any coding errors by means of diagnostic function, and if possible simulate thewhole operation to see that it is alright.5.Running the SystemBefore the start push-button is pressed, thoroughly ensure that the input and Output wiring arecorrectly connected according to the I/O Assignment.
Once confirmed, the actual operation ofthe PLC can now be started. You may need to debug along the way and fine tune the controlsystem if necessary. Test run thoroughly until it is safe to operate by anyone.1-141.INTRODUCTIONA SYSTEMATIC APPROACH TO PROGRAMMABLE CONTROLLER DESIGNUnderstand the desiredrequirement of theControl SystemConnect all Input andOutput devices to PC.Draw a general flowchartof the Control SystemCheck all Input andOutput connectionsList all input and outputpoints to the respectiveI/O points of the PLCTest Run ProgramTranslate the flowchart toLadder DiagramEditing SoftwareProgrammed the designedLadder Diagram into PLCNoIs ProgramO.K.?YesAlter the programaccordinglyStore program inEPROM etcSimulate theprogram and debugthe softwareNoIs ProgramO.K.?Systematicallydocument all drawingYesEnd1-151.qINTRODUCTIONProgrammable Controller ApplicationsThere are so many applications that you can find PLCs are use in the various industries.
Here are thelist of applications.•••••••••••••••••••••••Material HandlingConveyor SystemPackaging MachinePick and Place Robot ControlPump ControlSwimming PoolWater TreatmentChemical Processing PlantPaper and Pulp IndustriesGlass ManufacturingPrecast Concrete IndustriesCement ManufacturingPrinting IndustriesElectro-plating PlantsFood ProcessingMachine ToolsTobacco IndustriesPlastic Moulding machineSemi-conductor Manufacturing MachineSugar Manufacturing PlantPalm Oil Manufacturing PlantAir Condition ControlTV Manufacturing Plant•••••••••••••••••••Power Station PlantProcess Monitoring ControlElectrical/Electronic ApplianceManufacturingDisk Drive ManufacturingPetrol Chemical PlantTraffic Light SystemTrain Control Station systemPlastic Manufacturing IndustriesCar Manufacturing PlantIron and Steel MillDiary Product Manufacturing PlantBuilding AutomationTyre ManufacturingIntegrated Circuit Chip ManufacturingSewage Treatment PlantSecurity Control SystemLift Control SystemGenerator Control SystemAmusement Park Control1-161.qINTRODUCTIONConsider A Simple ProjectSuppose you wish to control the following robot’s movement.(Start button) PB1 (0)(Detect workpiece)PH1 (4)(check grasp work)(3)(clockwiserotation)LS3LS1 (1)(counterclockwiserotation)LS2 (2)SOL2 (1001)(1000) SOL1conveyor A (1003)(clockwiserotation)conveyor B(counterclockwiserotation)This kind of robot is seen in many automated factories.
As is apparent from the figure, this robotpicks up a work being carried on conveyor A, and places it on conveyor B.Although seemingly simple, executing this series of operations with electric devices and circuitry isharder than realized.Looking at the above figure closely will disclose that the robot performs one operation at a timewhen a given condition is met. Let’s analyze these operations and conditions.1.When the start button is pressed, the robot rotates its arm clockwise.2.When the robot arm has moved to the position of the work in conveyor A, the arm grasps thework.3.When the arm has grasped the work, it rotates counterclockwise.4.When the arm has rotated to the position of conveyor B, it releases the work.1-171.INTRODUCTION1.
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