2 It is an electronic device used for automation of industrial processes where output results must be produced in response to input conditions within the the bounded time, otherwise miscontrol will result.Thus a PLC is used to control, time and regulate the sequence of operations.“ It is a digital device that uses a programmable memory to store instructions and to implement functions in order to control machines and processes”.
3 PLC is important since all production processes go through a fixed repetitive sequence of operations that involve logical steps and decisions.Unlike general purpose computers, the PLC is designed for extended temperature ranges, dirty or dusty conditions, immunity to electrical noise, and resistance to vibration and impact.
4 industrial process sensors drivers forindustrial process sensorsthe status of switches,past values of dataand other working dataare stored.ControlUnitDataMemoryProgramOutputdevicesInputProcess SensorsProcess Actuators(motors)PCthe instructions for thelogical control sequenceare stored.drivers for industrial process actuators, such as solenoid switches, motors and valvesthrough which the logical sequencethat the PLC will execute is built and edited.
5 PLC Wait for 10s Wait for 20s ON OFF V1 L1 Tank 1 L2 V2 L3 2 L4 V3 ReservoirR1PV1L1L2V2L3L4V3R2PLCONOFFWait for 10sWait for 20s
6 Normally closed contact ProgrammingPLC programming is based on the use of Ladder Diagrams. Using these, writing a program is equivalent to drawing a switching circuit.The basic components in a ladder logic program are the contact and the coil.InputNormally open contactNormally closed contactOutput deviceInputs in seriesLogic ANDInputs in parallelLogic ORSpecial Instruction
7 EndX400Y 430X401X402Y 431Y 432X403X404X406Each rung must start with an input or a series of inputs and end with an output.Inputs and outputs are numbered, the notation used depends on the PLC manufacturer
8 A normally open start switch A normally open start switch. When the switch is closed, the coil is energizedIn case of a normally closed switch the coil is energized provided that the switch does NOT change.
9 Logic FunctionsThe coil is not energized unless two normally open switches are both closed(both changes their state), thus gives AND logic situation.C=A.BABCABInputsOutputCAB1
10 The coil is not energized until either one of 2 normally open switches is closed which thus gives an OR logic situation.C=A+BCABInputsOutputCAB1A
11 For the coil to be energized we require A to be closed and either B or C to be closed A.(B+C)BCADBInputsOutputABC1
14 Entering the programEach horizontal line i.e. rung on the ladder represents a line in the program and the entire ladder can be translated into a program using a keyboard with the graphic symbols for the ladder elements and then the program panel translates these symbols into machine language that is then stored in the PLC memory.
15 Develop a program that will cause output D to go true when switch A and switch B are closed or when switch C is closed.
16 Develop a program that will cause output D to be on when push button A is on, or either B or C are on.
17 Develop a Ladder Logic for a car door/seat belt safety system Develop a Ladder Logic for a car door/seat belt safety system. When the car door is open, and the seatbelt is not done up, the ignition power must not be applied. If all is safe then the key will start the engine.
18 Design a motor controller that has a forward and reverse button Design a motor controller that has a forward and reverse button. The motor forward and reverse outputs will only be on when one of the buttons is pushed. When both buttons are pushed the motor will not work.
19 A robot is used to unload processed parts of a machine into AGV, pick up a new part for processing from AGV and load it onto the machine. The AGV is to be dispatched after completion of the cycle. Construct a ladder logic diagram for the task.0301200221042201 AGV has arrived02 AGV is carryinga new part to be processed.03 AGV has space to storea processed part.04 Machine has a finished partto be unloaded20 Unload old part from machineonto AGV21 Pick new part from AGVand load onto machine22 Dispatch the AGV
20 Timers and CountersTimers: It counts time units. It is represented by the symbol below where the number indicated means that the following task will be performed after timer counts that number of time units (usually seconds).Counter: They are used when there is a need to count a specified number of contact operations e.g. where items pass along a conveyer into boxes, and when the specified number of items has passed into a box, the next item is diverted into another box. It is represented by the symbol below with the number indicting that the following step will be performed after the counter counts that number of times.TIM09#CT47#
21 TI Timer (with a limit of 10 s) 30 Fill die 31 Advance punch During the powder metallurgy process, a punch is used to press blended metal powder into a die. A pushbutton is used to start the process. When the start button is pressed, the die is filled with powder. The punch is then advanced and it applies pressure to the powder for a duration of 10 seconds, after which it is retracted. The pressed compact is then ejected from the die and then the cycle repeats. The cycle can be interrupted by pressing a stop button. If the stop button is pressed, the punch is required to retract (if it had been advanced) before the process is stopped. It is required to construct a ladder logic diagram for this task3130020133TI#10323401 Start button02 Stop buttonTI Timer (with a limit of 10 s)30 Fill die31 Advance punch32 Retract punch33 Eject part (i.e compact)34 Stop cycle
22 QuestionWhy a stop button must be normally closed (NC) and a start button must be (NO) ?????If a NC stop button is damaged, the machine will act as if the stop button was pushed and shut down safely. If a NO start button is damaged the machine will not be able to start