Presentation on theme: "Programmable Logic Controller PLC. It is an electronic device used for automation of industrial processes where output results must be produced in response."— Presentation transcript:
Programmable Logic Controller PLC
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”.
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.
Control Unit Data Memory Program Memory Output devices Input devices Process Sensors Process Actuators (motors) PC the instructions for the logical control sequence are stored. the status of switches, past values of data and other working data are stored. drivers for industrial process sensors drivers for industrial process actuators, such as solenoid switches, motors and valves through which the logical sequence that the PLC will execute is built and edited.
Tank 1 Tank 2 Reservoir R1 P V1 L1 L2 V2 L3 L4 V3 Reservoir R2 PLC ON OFF Wait for 10s Wait for 20s
Programming PLC 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. Input Normally open contact Input Normally closed contact Output device Inputs in series Logic AND Inputs in parallel Logic OR Special Instruction
End X400 Y 430 X401X402 Y 431 Y 432 X403X404 X406 Each 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
A normally open start switch. When the switch is closed, the coil is energized In case of a normally closed switch the coil is energized provided that the switch does NOT change.
Logic Functions A B C InputsOutput C AB The coil is not energized unless two normally open switches are both closed (both changes their state), thus gives AND logic situation. C=A.B A B
The coil is not energized until either one of 2 normally open switches is closed which thus gives an OR logic situation. C=A+B InputsOutput C AB C A B B A
For the coil to be energized we require A to be closed and either B or C to be closed A.(B+C) InputsOutput ABC B B C A D A C
InputsC AB C A B NAND InputsC AB A B C NOR C=
EOR A C B A B InputsC AB
Entering the program Each 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.
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.
Develop a program that will cause output D to be on when push button A is on, or either B or C are on.
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.
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.
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 AGV has arrived 02 AGV is carrying a new part to be processed. 03 AGV has space to store a processed part. 04 Machine has a finished part to be unloaded 20 Unload old part from machine onto AGV 21 Pick new part from AGV and load onto machine 22 Dispatch the AGV
Timers and Counters Timers: 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. TIM 09 # CT 47 #
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 task 01 Start button 02 Stop button TI Timer (with a limit of 10 s) 30 Fill die 31 Advance punch 32 Retract punch 33 Eject part (i.e compact) 34 Stop cycle TI #10 32 TI
Question Why 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