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					Programmable Logic Controller
• EVOLUTION OF PLC
   • HARD WIRED CONTROL
   • HARD WIRED SOLID STATE CONTROLLER
   • PROGRAMMABLE LOGIC CONTROLLER
• HARD-WIRED CONTROL
   • THE CONTROL TASKS WERE SOLVED WITH
     CONTACTOR OR RELAY CONTROL.
   • CIRCUIT DIAGRAM HAD TO BE DESIGNED.
   • ELECTRICAL COMPONENT INSTALLED.
   • WIRING LIST CREATED.
   • WIRE THE COMPONENTS NECESSARY TO
     PERFORM A SPECIFIC TASK.
Programmable Logic Controller
• HARD-WIRED CONTROL
 • THE CONTROL TASKS WERE SOLVED WITH
   CONTACTOR OR RELAY CONTROL.
 • CIRCUIT DIAGRAM HAD TO BE DESIGNED.
 • ELECTRICAL COMPONENT TO BE
   INSTALLED.
 • WIRING LIST TO BE CREATED.
 • WIRE THE COMPONENTS NECESSARY TO
   PERFORM A SPECIFIC TASK.
Programmable Logic Controller
• HARD-WIRED CONTROL
  • ADVANTAGE
   • RELATIVELY SIMPLE
   • LOW INITIAL COST
   • SMALL LOGIC COULD BE IMPLEMENTED
     MUCH FASTER.
 • DISADVANTAGE
   • CHANGE IN FUNCTION OR SYSTEM
     EXPANSION REQUIRED EXTENSIVE
     COMPONENT CHANGE AND REWIRING.
   • SPACE REQUIRED IS MORE.
   • DIAGNOSTICS BECOMES DIFFICULT FOR
     COMPLEX LOGIC
Programmable Logic Controller
• HARDWIRED SOLID STATE CONTROLLER
   • SYSTEM CONSISTING OF ELECTRONIC LOGIC
     DEVICES HARDWIRED IN A SPECIFIC
     CONFIGURATION.
• ADVANTAGES
   • SMALLER IN SIZE COMPARED TO RELAY
     LOGIC
   • LOW POWER CONSUMPTION.
   • ALLOWS ON LINE TESTING OF I/O CIRCUITS
     MANUALLY OR AUTOMATICALLY.
• DISADVANTAGES
   • DISCRETE COMPONENTS.
   • CONTROLLED ENVIRONMENT NEEDED.
   • NO WATCH DOG TIMER AVAILABLE.
Programmable Logic Controller
DEFINITION :
• A PROGRAMMABLE CONTROLLER IS A SOLID
  STATE CONTROLLER THAT MONITORS THE
  STATUS OF DEVICES CONNECTED AS INPUTS.
  BASED UPON A USER WRITTEN PROGRAM,
  STORED IN ITS MEMORY, IT CONTROLS THE
  STATUS OF DEVICES CONNECTED AS OUTPUTS.
Programmable Logic Controller
PLC INTRODUCTION:
• MODICON INTRODUCED THE FIRST PLC IN 1969
AS A REPLACEMENT FOR THE MASSIVE, HARD-
WIRED RELAY PANELS USED IN MANUFACTURING
PLANTS TO CONTROL MACHINE TOOLS AND
ASSEMBLY LINES.
• THE NOVEL FEATURE OF THIS NEW DEVICE IS
THAT IT IS PROGRAMMABLE.
• IT SAVES FACTORY FLOOR SPACE BY REPLACING
THE RELAY BASED SYSTEM.
• IT IS ALSO RE-PROGRAMMABLE FOR A
DIFFERENT APPLICATION.
• AN IMPROVEMENT OVER HARD-WIRED
SYSTEMS.
Programmable Logic Controller
ADVANTAGES
• COST EFFECTIVE FOR CONTROLLING COMPLEX
  SYSTEMS.
• FLEXIBLE AND CAN BE REAPPLIED TO CONTROL
  OTHER SYSTEMS QUICKLY AND EASILY.
• COMPUTATIONAL ABILITIES ALLOW MORE
  SOPHISTICATED CONTROL.
• TROUBLESHOOTING AIDS MAKE PROGRAMMING
  EASIER AND REDUCE DOWNTIME.
• RELIABLE COMPONENTS MAKE THESE LIKELY TO
  OPERATE FOR YEARS BEFORE FAILURE.
• PLCS HAVE INTEGRATED DIAGNOSTICS AND
  OVERRIDE FUNCTIONS.
• DIAGNOSTICS ARE CENTRALLY AVAILABLE.
Programmable Logic Controller
                             ARCHITECTURE
                                      Communication
                                         Port
                                                                           O   SOLENOID
                 I
PUSH BUTTON                                                                U   VALVE
                 N
                                                                           T
PROXIMITY        P                 CENTRAL PROCESSOR
                                                                           P   LAMP
SWITCH           U
                                                                           U
                 T
                                                                           T
                 S
                                                                           S
                                                                                  High
        High
                                                                                 Voltage
       Voltage
                                           MEMORY


                                 Program                 Data

                                           Low Voltage

                     AC Power Supply 85-                 DC power Supply
                                              OR
                     264 VAC, 50/60Hz
Programmable Logic Controller

          PLC OPERATING CYCLE
                   START

 House Keeping             Input Scan


 Output
  Scan



                                  Program
                                    Scan
Programmable Logic Controller
• INPUT PROCESSING:
    DURING I/P SCAN THE PLC READS THE
 ON/OFF STATUS OF INPUTS & STORES THEM IN
 THE I/P IMAGE MEMORY BEFORE EXECUTION
 OF PROGRAM.THIS INFORMATION IS STORED
 & HELD VALID TILL THE NEXT SCAN OF INPUT
 MODULE.NO CHANGE IN STATUS IS
 ACKNOWLEDGED IN BETWEEN SCAN
 SEQUENCE.
         Inputs             Read in
                          I/P IMAGE
         I/P              MEMORY
       MODULE               IN CPU
Programmable Logic Controller
• PROGRAM PROCESSING:
      THE PLC EXECUTES THE USER
 PROGRAM TAKING INTO CONSIDERATION THE
 STATUS FROM IMAGE MEMORIES & NOT THAT
 OF ACTUAL PHYSICAL ELEMENTS. DEPENDING
 UPON THE LOGIC,THE O/P IMAGE MEMORY IS
 UPDATED AS THE PROGRAM EXECUTION
 PROGRESSES & RESULT IS CONVEYED TO THE
 CPU MEMORY FOR INTERMEDIATE STORAGE.

 I/P IMAGE     LOGIC        O/P IMAGE
 MEMORY      PROCESSING     MEMORY
   IN CPU      IN UMC         IN CPU
Programmable Logic Controller
• OUTPUT PROCESSING:
    ON COMPLETING THE EXECUTION OF ALL
 INSTRUCTIONS (LOGIC SCAN) THE ABOVE
 STORED OUTPUT IMAGE MEMORY IS
 TRANSFERRED TO OUTPUT MODULE WHICH
 WILL PHYSICALLY CHANGE THE STATUS OF THE
 OUTPUT ON THE PLC MODULE.

 O/P IMAGE   Write out            Output
                           O/P
MEMORY IN                MODULE
   IN CPU
Programmable Logic Controller
FLOW CHART:
• A FLOW CHART IS A GRAPHICAL TOOL USED
  TO CREATING THE STRUCTURE OF A
  PROGRAM.
• A FLOW CHART OF A SINGLE SCAN ALWAYS
  BEGINS WITH READING THE INPUTS &
  UPDATING THE INPUT IMAGE,OR BUFFER,&
  ENDS WITH READING THE OUTPUT IMAGE &
  UPDATING THE OUTPUTS.
• THE FLOW OF INFORMATION,PRODUCT,TIME
  CAN ALSO SHOWN AS LINE LEADING FROM
  ONE EVENT OR PROCESS TO ANOTHER.
Programmable Logic Controller
    FLOW CHART OF A PLC SCAN

              READ INPUTS


          UPDATE INPUT IMAGE



        EVALUATE LADDER LOGIC
         UPDATE OUTPUT IMAGE



          READ OUTPUT IMAGE


           UPDATE OUTPUTS
Programmable Logic Controller
• PLC LADDER LOGIC IS A COMPUTER
  PROGRAM USED TO REPRESENT THE
  LOGIC TO BE EXECUTED.
• THE LADDER LOGIC IS EXECUTED
  SEQUENTIALLY AND REPETITIVELY.
• THE INPUT CANNOT PRODUCE AN
  RESPONSE UNTIL THE PLC HAS
  COMPLETED THE SEQUENCE OF
  OPERATION
Programmable Logic Controller

   RELAY LOGIC         LADDER LOGIC

REPRESENTATION OF   REPRESENTATION OF
 LOGIC IS FROM TOP LOGIC IS FROM LEFT TO
    TO BOTTOM              RIGHT
 THE EXECUTION OF    THE EXECUTION OF
      LOGIC IS            LOGIC IS
 SIMULTANEOUSLY     SEQUENTIALLY AND
                       REPETITIVELY
CALCULATION,COMP CALCULATION,COMPAR
   ARISION IS NOT   ISION IS POSSIBLE IN
 POSSIBLE IN RELAY     LADDER LOGIC
       LOGIC
Programmable Logic Controller
APPLICATION EXAMPLE:
START\STOP CIRCUIT FOR MOTOR:
• THIS IS USED TO START A DEVICE WITH A
  MOMENTARY INPUT.
• ONCE START PUSHBUTTON IS PRESSED,THE
  INPUT ENERGIZE INSTRUCTION WILL STAY ON
  UNTIL THE MOMENTARY STOP PUSHBUTTON IS
  PRESSED.
• OPERATION:
     TURN ON AN OUTPUT WITH A MOMENTARY
  INPUT,
  & KEEP IT ON UNTIL INSTRUCTED TO TURN IT
  OFF.
Programmable Logic Controller
• START THE MOTOR BY PRESSING THE
  START
  PUSHBUTTON. KEEP THE MOTOR
  RUNNING UNTIL STOP PUSHBUTTON IS
  PRESSED.
    STOP      START
    I0        I1         O/0
                        ( )
                           MOTOR
              O/0          STARTER
Programmable Logic Controller
Ladder Logic:
• The logic used to perform this consist of one rung.
• In this example the stop push button is normally
  closed switch but is programmed as a normally
  open instruction.
Rung 0
• Before any instructions are activated N.O.
  instruction I\O is true(since a N.C. pushbutton is
  wired to a input terminal I\O & that pushbutton
  has not been pushed) & N.O. instruction I\I is
  false.
Programmable Logic Controller
RUNG 0
• WHEN THE START PUSH BUTTON IS PRESSED
  N.O. INSTRUCTION I\I BECOMES TRUE,
  ENERGISING OUTPUT O\0.
• THE TRUE STATUS OF CONTROL INSTRUCTION
  O\0 IS REFLECTED IN N.O.CONDITION
  INSTRUCTION O\0,WHICH IS PROGRAMMED IN
  PARALLEL WITH THE START INSTRUCTION.
• THIS KEEPS THE OUTPUT ON EVEN WHEN I\I IS
  NO LONGER TRUE.
• WHEN THE STOP BUTTON IS PRESSED,N.O.
  INSTRUCTION I\O BECOMES FALSE, & THE
  OUTPUT IS DE-ENERGISED.
 Programmable Logic Controller
• Typical Input Card Circuit:


                Opto        Processing
                            Circuit      To-Processor
                Isolation

      1          2            3              4


 Field device
 & Input                            LED
 Filtering                    5
                                    Indication
Programmable Logic Controller
• Typical Output Card Circuit:

                                        Output
               Processing   Opto        Driving Circuit
               Circuit      Isolation

      1            2          3            4


   Processor
   (CPU)
                              5     LED
                                    Indication
Programmable Logic Controller
APPLICATIONS OF PLC:
 BUILDING CONTROLS: ANTI- THEFT SYSTEMS,
  ESCALATORS, GARAGE DOOR OPENERS, INDUSTRIAL
  ELEVATORS AND LIFTS, LIGHTING CONTROL.
 CHEMICAL PROCESSING EQUIPMENT: ANODIZING
  EQUIPMENT, ASPHALT EQUIPMENT & CHEMICAL KILNS.
 CIVIL ENGINEERING APPLICATIONS: AUTOMATIC
  WINDOW WASHERS, LOCK CONTROLS, PARKING LOT
  CONTROL, RAILROAD CROSSING CONTROL, STREET
  LIGHTING & TRAFFIC CONTROL.
 FURNACES , BURNERS , AND DRYERS: BOILER & BURNER
  MANAGEMENT , DRYING EQUIPMENT, INDUSTRIAL
  PROCESS FURNACES.
 GENERAL INDUSTRY EQUIPMENT: AIR COMPRESSOR,
  BOTTLE FILLERS, INDUSTRIAL CENTRIFUGES,
  LABELLING MACHINERY, PACKING MACHINERY&
  VACUUM SYSTEMS.
Programmable Logic Controller
  MAGNETIC FORCE MOES SPRING
  CONTACT DOWM WHEN THE COIL
    IS ENERGISED

 SPRING
 CONTACT                       NORMALLY CLOSED
                                  CONTACT

                                  NORMALLY OPEN
                                  CONTACT




           COIL    RELAY
Programmable Logic Controller
• RELAY
• REMOTE CONTROLLED SWITCH.
• CONTACTS ARE ACTIVATED BY ENERGISING
  THE COIL.
• COIL CREATES A MAGNETIC FIELD WHICH
  MOVES THE SPRING DOWNWARD
• ENERGISING THE COIL BREAKS THE NC
  CONTACT AND MAKES THE NO CONTACTS.
• SPRING RETURNS TO ITS INITIAL POSITION
  WHEN THE COIL IS DE-ENERGISED
Programmable Logic Controller
• TASK :- DUST SILO MOTOR TO BE RUN IN BOTH
  FORWARD AND REVERSE DIRECTION
Programmable Logic Controller
• RELAY LOGIC FOR ROTATING MOTOR IN
  FORWARD AND REVERSE DIRECTION
  P


                                      STOP
                                   PUSH BUTTON


       FORWARD                   REVERSE
      PUSH BUTTON              PUSH BUTTON


                          (RL-1)                     (RL-2)




                    REVERSE                      FORWARD
                    CONTACT                      CONTACT




                    FORWARD
                      RELAY                      REVERSE
                      (RL-1)                      RELAY
                                                  (RL-2)

  N
Programmable Logic Controller
• LADDER LOGIC FOR ROTATING MOTOR IN FORWARD
  AND REVERSE DIRECTION
   24 V +                                              24 V -
         I 1.1          I 1.3          O 0.2   O 0.1




         I 1.2          I 1.3          O 0.1   O 0.2




      I 1.1      FORWARD PUSH BUTTON INPUT


      I 1.3      STOP PUSH BUTTON INPUT


      O 0.2      REVERSE NC CONTACT

      O 0.1      FORWARD OUTPUT COIL


      I 1.2      REVERSE PUSH BUTTON INPUT


      I 1.3      STOP PUSH BUTTON INPUT

      O 0.1      FORWARD NC CONTACT


      O 0.2      REVERSE OUTPUT COIL

				
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