The document discusses programmable logic controllers (PLCs). It defines a PLC as a specialized computer used to control machines and industrial processes. PLCs can be programmed by people without computer programming skills. They work by receiving input from sensors, executing programmed logic to determine outputs, and sending output signals to control devices. PLCs have evolved from conventional computers in the 1960s-1970s and are now widely used in industrial applications like manufacturing due to benefits like flexibility, reliability, and cost effectiveness compared to custom controllers. The document outlines the main components and programming of PLCs including ladder logic.

1. Thesis on
Programmable Logic Controller (PLC)

2. Introduction
Programming is instructing a computer to do
something with the help of a programming
language. A programming language is an artificial
language designed to communicate instructions to
a machine. Programming languages can be used
to create programs that control the behavior of a
machine.

3. What is PLC ?
A programmable logic controller is a specialized
computer used to control machines process.
It uses a programmable memory to store
instructions and specific functions that include
ONOFF functions, timing, counting,
sequencing, arithmetic and data handling
It can be programmed, controlled and
operated by a person unskilled in operating
(programming) computers.

4. Aim and Objectives of PLC
Its purpose is to monitor crucial process
parameters and adjust process operation
accordingly.
Eliminates much of the hard wiring.
It is reprogrammable, reusable and reliable.
Can be connected with plant computer systems
easily.

5. History
 The first PLC systems evolved from conventional
computers in the late 1960s and early 1970s.
In 1990’s different ways of programming PLCs was
introduced and in some cases it took the place of PCs.
 The first PLC systems evolved from conventional
computers in the late 1960s and early 1970s.
 In the 1980's the lack of standardization were
improved and size of PLCs was also reduced.
 In 1990’s different ways of programming PLCs was
introduced and in some cases it took the place of
pc’s.

6. How PLC works
Receives information's through different sensors.
Sequentially executes programs according to
the information from input sensors.
Gives the solution of problems and sends
appropriate commands as output.

7. Main Parts of PLC
Input Module
Output Module
Processor
Memory
Power Supply
Programming Device

8. Diagram of PLC

9. Programming The PLC
It is mostly based on ladder logic. The sequential
approaches are:
Entry of the ladder logic diagram
Low-level computer-type languages
High-level computer type languages
Functional blocks
Sequential function chart

10. Concept of Ladder Logic
It is a programming language that represents a
program by a graphical diagram.
Programs in this language resemble ladders,
with two vertical rails and a series of horizontal
rugs between them.
Symbols of ladder logic
-( )- A regular coil,
-()- A “ not” coil,
-[ ]- A regular contact,
-[ ]- A not contact

11. PLC Processor Scan
Three major tasks in a PLC processor scan are
executed in the following order :
Read the physical inputs
Scan the ladder logic program
Write the physical outputs

12. Application of PLC
Some remarkable sectors using PLC application:
In Traffic light Signal system
In automatic transfer switch
In Nano technology and robotics
In industrial manufacturing
In medical instruments and technologies
In machining, packaging, material handling,
automated assembly etc.

13. PLC
Designed for extreme
industrial environments
Integrated command
interpreter (proprietary)
No secondary memory
available
Optimized for Single
task
Computer
Designed mainly for
data processing and
calculation
Optimized for speed
Lost of secondary
memory available
Multitasking capability
PLC Vs. Computer

14. Advantages
Flexibility
Large Quantities of Contacts
Lower Cost
Visual Observation
Reliability and Maintainability

15. Disadvantages
Single-function applications do not pay to use a
PLC that includes multiple programming
capabilities.
 Their operational sequence is seldom or never
changed.
 if the power fails, the system stops.

16. Future of PLC
Continuation of new product developments and
making integration of PLCs with other control.
 PLC technology include features such as GUIs
and more human-oriented machine interfaces.
New PLC instructions are developed to add
intelligence to a controller.
Concept of the flexible manufacturing system
(FMS) will determine the control philosophy of the
future.

17. Conclusion
PLC applications are typically highly customized
systems. PLC is low compared to the cost of a specific
custom-built controller design. In general, PLCs are
more robust and require less maintenance, thus
making the things they control work better, in spite of
the environment. Overall, PLCs appear to be an
excellent solution for many different problems.

18. THE END