This document provides an introduction to programmable logic controllers (PLCs) and ladder logic programming. It defines a PLC as a small computer used to automate industrial processes by monitoring inputs and making decisions to control outputs based on a stored program. The document outlines the basic components of a PLC including input and output modules and the central processing unit. It then introduces ladder logic as the most common programming language for PLCs, describing the basic symbols of ladder diagrams including contacts, coils, and rungs. Finally, it provides examples of ladder logic programs for AND, OR, and NOT logic operations as well as timers and counters.

1. Introduction to
Programmable
Logic Controllers
and Ladder Logic

2. Welcome
The purpose of this Presentation is to
give you a very simple look
Programmable Logic Controllers and its
programming using Ladder Logic.
There is no need for you to be
familiar in any way with this field.
The only requirement is that you
enter with an open mind.

3. To begin with..
What is
automation?

4. You may have come across the word
“automated” very usually!

5. Automation is the use of machines, control systems and information
technologies to monitor and control the production.
In other words, an automated system is any system
that require minimum or no human intervention.

6. Automation has made our life extremely
simple.

7. Earlier, processes were carried out by operator, hence
were much prone to human errors.

8. So we can imply that with
Industrial control,
factory automation,
and PLC
(if are done well),
we can save a lot of time,
materials, energy, and money.

9. Where do we begin?

10. Let’s recall the story of an
explorer in Africa who asked
the native tribesman,

11. How does one eat a huge animal like an
elephant?"
The tribesman looked at the explorer in
astonishment and replied, "We eat it just like
everything else, one bite at a time."

12. Simple as it is, industrial control
is comprised of many smaller
circuits. By exploring and
learning simple smaller circuits,
you can learn to build a complete
automated system.

13. Programmable logic controllers
Lets Start With…
What is

14. a small computer with a built-in operating system
which monitor inputs and other variable values,
make decisions based on a stored program, and
control outputs to automate a process or machine.
Programmable logic controllers
What is

15. Well, that was simple isn’t it ?
Lets put it in another way..

16. A PLC is similar to a computer which is designed to
be programmed once, and run repeatedly as needed.

17. Elements of PLC
Let’s have al look at..

18. Input Modules
Senses the input signal, isolates it and converts it to DC
level.

19. Central Processor Unit (CPU)
microprocessor system that contains the system memory
and its decision making unit very similar to that of a
computer’s CPU.
Input Modules
Senses the input signal, isolates it and converts it to DC
level.

20. Output Module
receives the convert control signals from the CPU and
them converts them into digital or analog values that can
be used to control various output devices.
Central Processor Unit (CPU)
microprocessor system that contains the system memory
and its decision making unit very similar to that of a
computer’s CPU.
Input Modules
Senses the input signal, isolates it and converts it to DC
level.

21. Programming Device
Personal computer or a Laptop
And Communication Cable
Output Module
receives the convert control signals from the CPU and
them converts them into digital or analog values that can
be used to control various output devices.
Central Processor Unit (CPU)
microprocessor system that contains the system memory
and its decision making unit very similar to that of a
computer’s CPU.
Input Modules
Senses the input signal, isolates it and converts it to DC
level.

22. PLC scan
What is a

23. Reads
Inputs
Execute
Programs
Diagnostics &
Communication
Updates
Outputs
PLC scan

24. PLC scan

25. Programming PLC

26. The first and still most popular
programming language used
with PLC is Ladder Logic
Programming (LAD).

27. They are called "ladder" diagrams
because they resemble a ladder,
with two vertical rails (supply
power) and as many "rungs"
(horizontal lines).
The first and still most popular
programming language used
with PLC is Ladder Logic
Programming (LAD).

28. Basic Ladder Logic Symbols
Normally Open (NO) contact
Passes power (on) when coil driving the contact is on.
Contacts

29. Normally Closed (NC) contact
Passes power (on) when coil driving the contact is off.
Basic Ladder Logic Symbols
Normally Open (NO) contact
Passes power (on) when coil driving the contact is on.
Contacts

30. Output or Coil
When power flows through the Coils via contacts they are
energized.
Basic Ladder Logic Symbols

31. Schematic of ladder diagram

32. Selecting a PLC
Criteria
• Number of logical inputs and outputs.
• Memory
• Number of special I/O modules
• Scan Time
• Communications
• Software

33. Functional Operation
AND Operation
OR Operation
NOT Operation

34. Lets have a look at their truth table
and Ladder Logic diagram

35. 35
AND Operation
Both inputs S4 and S5 must be true (1) in order for
the output L3 to be true (1).
Ladder diagram

36. OR Operation
Ladder diagram
Either input S1 or S2 is true (1), or both are true,
then the output L2 is true (1).

37. 37
NOT Operation
If input S1 is be true (1), then the output L1 is true (0) or when A is (0),
output C is 1.
Ladder diagram

38. Programming Functions
Timers
Counters

39. Timers
 On-Delay Timer (TON)
 Off-Delay Timer (TOF)
 Retentive On-Delay Timer (TONR)

40. Counters
 Count UP Counter (CTU)
 Count DOWN Counter (CDU)
 Count UP/DOWN Counter (CTUD)

41. ProgrammingExamples
Lets start with simple examples…

42. Programming Examples
 D = (A AND B) OR C

43. Programming Examples
Triggering the Relay Coil

44. Ladder Diagram for Triggering the
Relay Coil

45. Learn the Basics of
Programming Logic
Controller & Ladder
Logic by Downloading
this E-book

46. This E-book contains
Programmable logic controllers
PLC Scan
Basic Ladder Logic Symbols
Functional Operation
Programming Functions
Programming To PLC (Practical Examples)
Illustration of PLC Scan

47. For Further Reading
Introduction to Programmable Logic Controller
and Ladder Logic