Programmable Logic Controller

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Information about Programmable Logic Controller

Published on December 11, 2010

Author: montass783


PROGRAMMABLE LOGIC CONTROLLERS(PLC) : PROGRAMMABLE LOGIC CONTROLLERS(PLC) By : DIMASSI MONTASSAR. Slide 2: Problematic: What are the PLC’s components? What are the PLC’s operations? Haw to create the PLC’s programs? What are the advantages and disadvantages of PLCs? Outline: : Outline: Introduction. PLC Components. PLC Operations. PLC Programs. Advantages and Disadvantages. Conclusion. Introduction : Introduction What does ‘PLC’ mean? A PLC (Programmable Logic Controllers)  is an industrial computer used to monitor inputs, and depending upon their state make decisions based on its program or logic, to control (turn on/off) its outputs to automate a machine or a process. Slide 5: PLC’s History: Developed to replace relays in the late 1960s. PLC began in the 1970s, and has become the most common choice for manufacturing controls. The PLC was invented in response to the needs of the American automotive manufacturing industry (primarily General motors). Costs dropped and became popular by 1980s. Now used in many industrial designs. Slide 6: Need for PLCs: Flexible and can be reapplied to control other systems quickly and easily. Computational abilities allow more sophisticated control. Reliable components make these likely to operate for years before failure. Slide 7: Types of PLCs: There are several different types of PLCs, but generally we use one of this tow PLCs: COMPONENTS OF PLC : COMPONENTS OF PLC Processor. Memory unit. Power supply. Input/Output Modules. Programming device. Slide 10: Processor: Processor is the central processing units (CPU) of the programmable controller, it executes the various logic and sequencing functions by operating on the PLC inputs to determine the appropriate output signals. Slide 11: Memory unit: Memory unit is connected to the CPU, which contains the programs of logic, sequencing and I/O operation. This memory unit is referred to as the user or application memory because its contains are entered by the user and also direct the execution of control program and coordinates I/O operations with the aid of system memory. Slide 12: Power supply: A power supply of 120v alternating current (ac) used to drive the PLC (some units operate on 240v ac) The power supply converts the 120v (ac) into direct current (dc) voltages of ± 24 v. These low voltages are used to operate equipment that many have much higher voltage and power ratings than the PLC itself. Slide 14: Input/Output Modules: Input Module: Input to the PLC are signals come from: Limit-switchs, Pushbuttons, Sensors, And other on/off devices. Slide 16: Output Module: Outputs from the controller are on/off signals to operate: Motors, Valves, And other devices required to actuate the process. Slide 17: Programming device: Programming device is used to entered the required program into the memory of the processor. PLC Operations : PLC Operations The PLC program is executed as part of a repetitive process referred to as a scan. Slide 19: A PLC scan starts with the CPU reading the status of inputs. The application program is executed using the status of the inputs. Once the program is completed, the CPU performs internal diagnostics and communication tasks. The scan cycle ends by updating the outputs, then starts over. The cycle time depends on the size of the program, the number of I/Os, and the amount of communication required. PLC Programs: : PLC Programs: Programming is done through programming terminal. Programming terminal translates engineering language (logic control) to machine language (binary code) Slide 21: Most PLC manufacturers offer software packages that allow a standard computer to be used as a programming terminal: Examples: - SYSWIN 34 for OMRON - STEP 7 for SIMENS Slide 22: Programming Languages: Programming languages used to program a PLC. LADDER DIAGRAM: Ladder logic is the most commonly used PLC programming language. Ladder logic programming has been expanded to include such functions as counters, timers ,shift registers and math operations. Slide 23: Symbols for PLC programming: Input instructions: - Normally Open (NO) instruction: - Normally Closed (NC) instruction: Slide 24: Output instructions: Out instruction : The Out instruction is sometimes also called an Output Energize instruction. The output instruction is like a relay . OR Out Bar instruction: The out bar instruction is like a normally closed relay. OR Slide 25: PLC Functions: Counters: A counter is a simple device intended to do only one thing, is to count. To use them we must know 3 things: Where is the pulse that we want to count. How many pulses we want to count before the react. When/how we reset the counter so it can count again. Slide 26: Example: Here we want to count 5 widgets from input 0001 before turning on output 0500. Input 0002 will reset the counter. Slide 27: Timers: It is an instruction that waits a set amount of time before doing the react. To work with timers, we must know tow things: What will enable the timer. How long we want to delay before the react. Slide 28: Example: Slide 29: Example of a complete ladder diagram: Advantages/ Disadvantages : Advantages/ Disadvantages Advantages of PLC’s: -Reliable in operation. -Flexibility in programming and reprogramming in the plant. -Online/offline modifications. -Cost effective for controlling complex systems. -Small physical size, shorter project time. -Speed of operation. -Ability to communicate with computer systems in the plant. -Ease of maintenance /troubleshooting. -Documentation. -Security. Slide 31: Disadvantages of PLC’s: Most PLCs manufacturers offer only closed architectures for their products . PLC devices are proprietary which limits the design and cost options. CONCLUSION : CONCLUSION Finally, we summaries that our presentation takes the basic PLC’s knowledge; But, according the products of PLC’s factories and their various models we must know how to choose the correct one wish it satisfies our needs. References : References www.plcmanual .com Introduction for PLC’s Wekipedia Slide 34: Thank You

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