The document discusses programmable logic controllers (PLCs). It provides a definition of a PLC as a digital computer designed for industrial control applications. The document outlines the history of PLCs, which were introduced in the 1960s to replace relay-based controls. It describes the major components of a common PLC, including a processor, power supply, input/output modules, and a programming device. The document discusses ladder logic as a common PLC programming language and provides an example ladder logic diagram for starting and stopping a motor. It also lists some advantages of PLCs like reliability, flexibility, and cost-effectiveness, as well as some disadvantages such as proprietary components. Applications of PLCs include robotics

1. PROGRAMMABLE
LOGIC CONTROLLER
Presented by
Krishna Kumar
(1316221007)
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2. CONTENTS
What is PLC?
History of PLC
Major components of PLC
Ladder logic
Advantages
Disadvantages
Application
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3. DEFINITION OF PLC
PLC is a digital computer designed for multiple inputs
and output arrangements, extended temperature
ranges, immunity to electrical noise, and resistance to
vibration and impact. A PLC is an example of a real
time system.
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4. PLC was introduced in late 1960’s
First commercial & successful Programmable Logic Controllers
was designed and developed by Modicon as a relay replacer for
General Motors.
Earlier, it was a machine with thousands of electronic parts.
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5. 5
MAJOR COMPONENTS OF A
COMMON PLC
PROCESSOR
POWER
SUPPLY
I M
N O
P D
U U
T L
E
O M
U O
T D
P U
U L
T E
PROGRAMMING
DEVICE
From
SENSORS
Pushbuttons,
contacts,
limit switches,
etc.
To
OUTPUT
Solenoids,
contactors,
alarms
etc.
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6. 6
MAJOR COMPONENTS OF
A COMMON PLC
POWER SUPPLY
Provides the voltage needed to run the primary PLC components
I/O MODULES
Provides signal conversion and isolation between the internal logic- level
signals inside the PLC and the field’s high level signal.
PROCESSOR
Provides intelligence to command and govern the activities of the entire PLC
systems.
PROGRAMMING DEVICE
Used to enter the desired program that will determine the sequence of operation
and control of process equipment or driven machine.
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7. PROGRAMMING LANGUAGES
OF PLC
Most common languages encountered in PLC programming
are:
1) Ladder Logic
2) Functional Block Diagram
3) Sequential Function Chart
4) Boolean mnemonics
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8. Ladder Logic
 It is well suited to express Combinational logic.
 The main ladder logic symbols represent the elements :
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9. NOR Gate
A B Y
A B Logic(Y)
OFF
OFF
ON
ON
OFF
ON
OFF
ON
ON
ON
ON
OFF
A B Logic(Y)
OFF
OFF
ON
ON
OFF
ON
OFF
ON
ON
OFF
OFF
OFF
NAND Gate
B
Y
A
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10. Ladder Logic Program for Start/Stop of Motor :
X2X1
Y1
Y1
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11.  Reliability.
 Flexibility in programming and reprogramming.
 Cost effective for controlling complex systems.
 Small physical size, shorter project time.
 High speed of operation.
 Ability to communicate with computer systems in the
plant.
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12. Disadvantages of PLCs
PLC devices are proprietary it means that part or
software of one manufacturer can’t be used in
combination with parts of another manufacturer.
Limited design and cost option
Fixed Circuit Operations.
PLCs manufacturers offer only closed architectures.
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13. Wherever automation is desired the PLCs are best
suited to meet the task.
Few examples of industries where PLCs are used :
1) Robots manufacturing and control
2) Car park control
3) Train control station system
4) Food processing
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14. Conclusion
 Programmable logic controller or plc as it universally
called is of industrial automation.
 Plc have been gaining popularity on the factory floor.
 For some time to core plc are an application area where
much can be done .
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15. Thank You
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