Programmable Logic Controller

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Programmable Logic controller introduction

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Programmable Logic Controller

  1. 1. PRESENTATION ON PROGRAMMABLE LOGIC CONTROLLER HIMSHEKHAR DAS 11-1-3-042 GNYANDEEP BISWAS 11-1-3-0481
  2. 2. OBJECTIVES 1. What is a PLC and Why was it developed 2. Familiarization with major components of PLC 3. PLC Operation 4. Ladder Logic 5. Simple Ladder Logic Program 6. PLC Features 7. Ladder Diagram of a DC Motor Control Circuit 2
  3. 3. INTRODUCTION  PLC is a digital computer used for automation of electromechanical processes such as control of machinery on factory assembly lines , amusement rides. PLC’s have multiple inputs and outputs and are designed for extended temperature ranges, immunity to electrical noise etc The control program is stored in non-volatile memory 3
  4. 4. WHY PLC WAS DEVELOPED Before the PLC, control was done using relays, drum sequencers, closed loop control system. Since they could number in thousands the process of updating such facilities was time consuming and expensive. Digital computer were now used .But these computers required the following attributes: tolerating the shop floor environment , require less training for use ,have fast response time Hence the PLC was developed and it came into use 4
  5. 5. DEVELOPMENT  PLC’s were designed to replace relay logic PLC’s were programmed using ladder logic (similar to schematic diagram representation of relay logic) or instruction list programming Mordern PLC’s are programmed using State logic ,BASIC,C 5
  6. 6. 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. 6
  7. 7. Major Components of a Common 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. 7
  8. 8. Major Components of a Common PLC 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. 8
  9. 9. 9 PLC INPUTS OUTPUTS MOTOR LAMP CONTACTOR PUSHBUTTONS
  10. 10. PLC Operation Basic Function of a Typical PLC Read all field input devices via the input interfaces, execute the user program stored in application memory, then, based on whatever control scheme has been programmed by the user, turn the field output devices on or off, or perform whatever control is necessary for the process application. This process of sequentially reading the inputs, executing the program in memory, and updating the outputs is known as scanning. 10
  11. 11. While the PLC is running, the scanning process includes the following four phases, which are repeated continuously as individual cycles of operation: PHASE 2 Program Execution PHASE 3 Diagnostics/ Comm PHASE 4 Output Scan PHASE 1 Read Inputs Scan 11
  12. 12. PHASE 1 – Input Status scan  A PLC scan cycle begins with the CPU reading the status of its inputs. PHASE 2– Logic Solve/Program Execution  The application program is executed using the status of the inputs PHASE 3– Diagnostics  Once the program is executed, the CPU performs diagnostics and communication tasks •An output status scan is then performed, whereby the stored output values are sent to actuators and other field output devices. The cycle ends by updating the outputs. •As soon as Phase 4 are completed, the entire cycle begins again with Phase 1 input scan. PHASE 4 - Output Status Scan 12
  13. 13. LADDER LOGIC  Each device in the relay rack is represented by a symbol on the ladder diagram with connections between those devices  Used to develop software for programmable logic controllers used in control applications  Used in conjunction with HMI interface  Ladder logic can be thought of as a rule based language rather than procedural language. A “rung” in the ladder represents a rule 13
  14. 14. A SIMPLE LADDER LOGIC PROGRAM Pre-requisite  Ladder diagram is read from top to bottom or from left to right The vertical lines are called rails . They provide power to the circuitry. AC or DC power may be connected The horizontal lines are called rungs .They are composed of input or output. Output from a PLC is called coil. A coil may be a motor , pump etc. 14
  15. 15.  Inputs/Sensors to a PLC are referred to as Contacts and may consist of switches, buttons, etc. Contacts begin in one of two states normally open or normally closed.  These contacts have an initial and follow-on state  Stop buttons are given a higher order of importance and therefore be shown ahead of other devices.  The normal condition of electrical diagrams is the circuit de-energized and with no external forces such as pressure, flow, etc. acting on the device. 15
  16. 16. L1 L2 Ladder Rail Ladder Rung Schematic Ladder Diagram. INPUT OUTPUT 16
  17. 17. 17 OFF Logic 0 IN PLC Input Module 24 V dc ON Logic 1 IN PLC Input Module 24 V dc
  18. 18.  All contacts associated with a device change state when the device is energized  Devices that perform a STOP function are normally placed in series on a rung  Devices that perform a START function are normally placed in parallel or in a branch configuration. Some commonly used ladder symbols :  -( )- : A regular coil energized when rung is closed  -() : A “not” coil , energized when rung is open  -[ ]- : A regular contact, closed whenever its corresponding coil is energized  -[]- :A “not” contact , closed whenever its coil is not energized  -- -- :Boxes represent various functions such as timers ,counters , etc. 18
  19. 19.  Logical AND : |--------[ ]----------[ ]-----------( )------ key 1 key 2 dc motor when the normally open contacts of both the switches close , electricity is able to flow and the dc motor starts  Logical AND with NOT : |------------[ ]------------[]-------------( )-------- close door obstruction door motor The above realizes the function : Door Motor The circuit shows a pushbutton that closes a door and a obstruction detector that senses if something is in the way of closing the door. When the normally open pushbutton closes and there is no obstruction the normally closed obstruction detector is closed and current is able to flow. 19
  20. 20. CIRCUIT 1 CIRCUIT 2 20
  21. 21. PROGRAMMING  Early PLC’s were programmed using proprietary programming panels which had dedicated function keys representing the various logical elements of PLC programs  Recently PLC’s are programmed using application software on personal computers, the software allows entry and editing of the ladder style logic 21
  22. 22. FUNCTIONALITY  Primary functionality includes relay control , motion control , process control , distributed control systems and networking  Programmable logic relay are used in light industry where only a few points of I/O are involved and low cost is desired 22
  23. 23. More About PLC  FEATURES  SCAN SYSTEM SCALE USER INTERFACE  COMMUNICATION  PLC PROGRAMMING 23
  24. 24. Tank Used to Mix Two Liquids A B C FS MOTOR TIMER FLOAT SWITCH SOLENOIDS SOLENOID 1 -MINUTE 24
  25. 25. DC MOTOR STARTING CIRCUIT 25
  26. 26. 26
  27. 27. 27

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