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PLC: Programmable Logical Controller
CONTENTS
1. What is PLC
2. Electrical Ladder Logic Diagrams
3. Software Ladder Logic Diagrams
4. PLC Implementation
5. An example

lecture note 9 PLC

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1. PLC - Introduction
What does PLC stand for?
PLC - programmable logic controller
PLC implements logic control functions by means
of a program

lecture note 9 PLC

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1. PLC - Introduction
Features

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1. PLC - Introduction
Features

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1. PLC - Introduction
An application example 1: Gate Control

PLC can sense a vehicle at the entrance or exit, and
open and close the gate automatically
The current vehicle count is easily determined by
programming a simple counter
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1. PLC - Introduction
An application example 2: Conveyor System

PLC can be used to start/stop latching logic for motor
control
Counters can be used for monitoring product amounts
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1. PLC - Introduction
Comparing traditional and programmable control systems - 1

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1. PLC - Introduction
Comparing traditional and programmable control ystems - 2
In traditional control, the switches S1, S2 and S3 must close for
K1 to be turned on - the wiring makes the rule
In PLC systems, the program is written to perform the logic when
S1 is closed AND S2 is closed AND S3 is closed, THEN turn on
K1 - the program makes the rule

It is much simpler to change program then wiring!

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1. PLC - Introduction
How does a PLC differ from a computer?
A computer is optimized for calculation and display tasks
A computer is programmed by specialists
A PLC is designed for (logic) control and regulation tasks
A PLC is programmed by non-specialists
A PLC is well adapted to industrial environment

lecture note 9 PLC

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1. PLC - Introduction
Why are PLCs so common?
They are cost-effective
They are flexible, reliable and compact
They have significant advantages over traditional
control systems based on relay or pneumatics

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1. PLC - Introduction
Where are PLCs used?
In every industry where automation is involved,
from individual machines to whole processes

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1. PLC - Introduction
What tasks do PLCs perform?
The logic control tasks such as interlocking,
sequencing, timing and counting (previously
undertaken with relays or pneumatics)
In addition, PLCs can perform a variety of
calculation, communication and monitoring tasks

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1. PLC - Introduction

Communication
Ports (RS-485)

Outputs & Power Supply

Inputs
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1. PLC - Introduction
Structure of a PLC

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1. PLC - Introduction
The PLC processor

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1. PLC - Introduction
PLC Input/Output Devices

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1. PLC - Introduction
PLC Input Devices
Push buttons
Switches (limit switches, level switches, etc.)
Sensors
...

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1. PLC - Introduction
PLC Output Devices
Relay contacts
Solenoid valves
Signal devices (such as lamps, alarms, etc.)
Motors
...

lecture note 9 PLC

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1. PLC - Introduction
Programming terminal

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1. PLC - Introduction
Programming is done through programming
terminal
Programming terminal translates engineering
language (logic control) to machine language
(binary code)

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1. PLC - Introduction
Programming through standard computer
Most PLC manufacturers offer software packages
that allow a standard computer to be used as a
programming terminal

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1. PLC - Introduction
Programming through standard computer

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1. PLC - Introduction
Relating the program to inputs and outputs
The CPU reads the data from the inputs
The program in the CPU uses the inputs to
evaluate the control logic. As the program runs,
the CPU updates the data
The CPU writes the data to the output

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1. PLC - Introduction
Relating the program to inputs and outputs

lecture note 9 PLC

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1. PLC - Introduction
Data Flow in the PLC

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1. PLC - Introduction
One of the advantages of PLC is that it can be programmed by
non-specialists
Program can be written either in the form of a
statement list: a set of mnemonic instructions representing a
function of the CPU
or a
ladder diagram: a graphical language resembling the
electrical relay diagrams

lecture note 9 PLC

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1. PLC - Introduction
statement list

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1. PLC - Introduction
Ladder diagram

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Note 8 plc introduction

  • 1. PLC: Programmable Logical Controller CONTENTS 1. What is PLC 2. Electrical Ladder Logic Diagrams 3. Software Ladder Logic Diagrams 4. PLC Implementation 5. An example lecture note 9 PLC 1
  • 2. 1. PLC - Introduction What does PLC stand for? PLC - programmable logic controller PLC implements logic control functions by means of a program lecture note 9 PLC 2
  • 3. 1. PLC - Introduction Features lecture note 9 PLC 3
  • 4. 1. PLC - Introduction Features lecture note 9 PLC 4
  • 5. 1. PLC - Introduction An application example 1: Gate Control PLC can sense a vehicle at the entrance or exit, and open and close the gate automatically The current vehicle count is easily determined by programming a simple counter lecture note 9 PLC 5
  • 6. 1. PLC - Introduction An application example 2: Conveyor System PLC can be used to start/stop latching logic for motor control Counters can be used for monitoring product amounts lecture note 9 PLC 6
  • 7. 1. PLC - Introduction Comparing traditional and programmable control systems - 1 lecture note 9 PLC 7
  • 8. 1. PLC - Introduction Comparing traditional and programmable control ystems - 2 In traditional control, the switches S1, S2 and S3 must close for K1 to be turned on - the wiring makes the rule In PLC systems, the program is written to perform the logic when S1 is closed AND S2 is closed AND S3 is closed, THEN turn on K1 - the program makes the rule It is much simpler to change program then wiring! lecture note 9 PLC 8
  • 9. 1. PLC - Introduction How does a PLC differ from a computer? A computer is optimized for calculation and display tasks A computer is programmed by specialists A PLC is designed for (logic) control and regulation tasks A PLC is programmed by non-specialists A PLC is well adapted to industrial environment lecture note 9 PLC 9
  • 10. 1. PLC - Introduction Why are PLCs so common? They are cost-effective They are flexible, reliable and compact They have significant advantages over traditional control systems based on relay or pneumatics lecture note 9 PLC 10
  • 11. 1. PLC - Introduction Where are PLCs used? In every industry where automation is involved, from individual machines to whole processes lecture note 9 PLC 11
  • 12. 1. PLC - Introduction What tasks do PLCs perform? The logic control tasks such as interlocking, sequencing, timing and counting (previously undertaken with relays or pneumatics) In addition, PLCs can perform a variety of calculation, communication and monitoring tasks lecture note 9 PLC 12
  • 13. 1. PLC - Introduction Communication Ports (RS-485) Outputs & Power Supply Inputs lecture note 9 PLC 13
  • 14. 1. PLC - Introduction Structure of a PLC lecture note 9 PLC 14
  • 15. 1. PLC - Introduction The PLC processor lecture note 9 PLC 15
  • 16. 1. PLC - Introduction PLC Input/Output Devices lecture note 9 PLC 16
  • 17. 1. PLC - Introduction PLC Input Devices Push buttons Switches (limit switches, level switches, etc.) Sensors ... lecture note 9 PLC 17
  • 18. 1. PLC - Introduction PLC Output Devices Relay contacts Solenoid valves Signal devices (such as lamps, alarms, etc.) Motors ... lecture note 9 PLC 18
  • 19. 1. PLC - Introduction Programming terminal lecture note 9 PLC 19
  • 20. 1. PLC - Introduction Programming is done through programming terminal Programming terminal translates engineering language (logic control) to machine language (binary code) lecture note 9 PLC 20
  • 21. 1. PLC - Introduction Programming through standard computer Most PLC manufacturers offer software packages that allow a standard computer to be used as a programming terminal lecture note 9 PLC 21
  • 22. 1. PLC - Introduction Programming through standard computer lecture note 9 PLC 22
  • 23. 1. PLC - Introduction Relating the program to inputs and outputs The CPU reads the data from the inputs The program in the CPU uses the inputs to evaluate the control logic. As the program runs, the CPU updates the data The CPU writes the data to the output lecture note 9 PLC 23
  • 24. 1. PLC - Introduction Relating the program to inputs and outputs lecture note 9 PLC 24
  • 25. 1. PLC - Introduction Data Flow in the PLC lecture note 9 PLC 25
  • 26. 1. PLC - Introduction One of the advantages of PLC is that it can be programmed by non-specialists Program can be written either in the form of a statement list: a set of mnemonic instructions representing a function of the CPU or a ladder diagram: a graphical language resembling the electrical relay diagrams lecture note 9 PLC 26
  • 27. 1. PLC - Introduction statement list lecture note 9 PLC 27
  • 28. 1. PLC - Introduction Ladder diagram lecture note 9 PLC 28