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Programmable Logic Controller


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Overview of PLC

Published in: Engineering
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Programmable Logic Controller

  1. 1. By Bipin Likhar
  2. 2. PLC  A Programmable Logic Controller (PLC) is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, control of amusement rides, or control of lighting fixtures.
  3. 3. PLC was introduced in late 1960’s to remove relay’s based system. First commercial & successful Programmable Logic Controllers was designed and developed by Modicon as a relay replacer for General Motors. Earlier, it was a machine with thousands of electronic parts. Later ,in late 1970’s,the microprocessor became reality & greatly enhanced the role of PLC permitting it to evolve form simply relay to the sophisticated system as it is today.
  4. 4. 4 Major Components of a Common PLC PROCESSOR POWER SUPPLY I M N O P D U U T L E O M U O T D P U U L T E PROGRAMMING DEVICE From SENSORS Pushbuttons, contacts, limit switches, etc. To OUTPUT Solenoids, contactors, alarms etc.
  5. 5. Major Components of PLC  POWER SUPPLY Provides the voltage needed to run the primary PLC components  I/O MODULES Provides signal conversion and isolation between the internal logic level signals inside the PLC and the field’s high level signal.  PROCESSOR Provides intelligence to command and govern the activities of the entire PLC systems.  PROGRAMMING DEVICE Used to enter the desired program that will determine the sequence of operation and control of process equipment or driven machine.
  6. 6. PLC Operation
  7. 7. Programming a PLC  Ladder Logic  Functional block diagram  Structural text(similar to Pascal)  Instruction list(similar to assembly language)
  8. 8. Why PLC ?.... • The controller is designed in modular form, so that sub- assemblies could be removed easily for replacement or repair. • A PLC can work in the harsh and extreme conditions of the industry where other systems such as a Micro-Controller cannot. • The system becomes reusable. • The method used to program the controller is simple, so that it can be easily understood by plant personnel.
  9. 9. Programmable Automation Controller
  10. 10. PAC  PAC stands for Programmable Automation Controller.  PLC is best suited for machine control but has limited memory and a focus on discrete I/O with on/off control.  On the other hand , a PAC is geared more toward complex automation system architectures composed of a number of PC-based software applications
  11. 11. Features of PAC  Composed of a number of PC-based software applications  Including HMI (human machine interface) functions  Architecture based on Ladder logic  Provide greater flexibility in programming  Larger memory capacity
  12. 12. Advantages of PACs over PLCs  More open architecture  Modular design  More analog I/O options  Better process control capabilities  More built in communication ports  Programming over USB ports  Tag based programming (one software package capable of programming multiple models )
  13. 13. Thank You