PROGRAMMABLE LOGICCONTROLLERS (PLC): AN     OVERVIEW
1.3 PRINCIPLES OFOPERATION  © 2011, The McGraw-Hill Companies, Inc
Mixer Process Control Problem                                         •   A mixer motor is to be                          ...
Hardwired relay method for control of motor   The motor starter coil (M) is energized when both thepressure and temperatur...
PLC method for control of motor The same input field devices                   Field devices are(pressure switch, temperat...
PLC method for control of motorThe same output field                        Starter coil isdevice (motor starter          ...
Enter the PLC ladder logic program into the memory                        of the CPU.•   The symbols represent instruction...
•   For the program to operate, the controller is placed in the RUN    mode.•   During each scan the controller examines t...
LogicPro simulation of the PLC program Input                                            Ladder Logic Program         Outpu...
Typical wiring required to implement the process control          scheme using a fixed PLC controller.        © 2011, The ...
END….© 2011, The McGraw-Hill Companies, Inc
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1.3 principles of operation

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1.3 principles of operation

  1. 1. PROGRAMMABLE LOGICCONTROLLERS (PLC): AN OVERVIEW
  2. 2. 1.3 PRINCIPLES OFOPERATION © 2011, The McGraw-Hill Companies, Inc
  3. 3. Mixer Process Control Problem • A mixer motor is to be used to automatically stir the liquid in a vat when the temperature and pressure reach preset values. • Manual operation of the motor is provided by means of a separate pushbutton station.© 2011, The McGraw-Hill Companies, Inc
  4. 4. Hardwired relay method for control of motor The motor starter coil (M) is energized when both thepressure and temperature switches are closed or when the manual pushbutton is pressed. © 2011, The McGraw-Hill Companies, Inc
  5. 5. PLC method for control of motor The same input field devices Field devices are(pressure switch, temperature hardwired to an switch, and pushbutton) are input module. used. © 2011, The McGraw-Hill Companies, Inc
  6. 6. PLC method for control of motorThe same output field Starter coil isdevice (motor starter hardwired to an coil) is used. output module. © 2011, The McGraw-Hill Companies, Inc
  7. 7. Enter the PLC ladder logic program into the memory of the CPU.• The symbols represent instructions and the numbers represent the instruction’s addresses.• Each input and output device is given an address, which lets the PLC know where it is connected. © 2011, The McGraw-Hill Companies, Inc
  8. 8. • For the program to operate, the controller is placed in the RUN mode.• During each scan the controller examines the status of input devices, executes the user program, and changes outputs accordingly.• The coil O/1 is energized when contacts I/1 and I/2 are closed or when contact I/3 is closed.• Either of these conditions provides a continuous logic path across the rung that includes the coil. © 2011, The McGraw-Hill Companies, Inc
  9. 9. LogicPro simulation of the PLC program Input Ladder Logic Program OutputModule Module © 2011, The McGraw-Hill Companies, Inc
  10. 10. Typical wiring required to implement the process control scheme using a fixed PLC controller. © 2011, The McGraw-Hill Companies, Inc
  11. 11. END….© 2011, The McGraw-Hill Companies, Inc

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