1. Seminar on "PLC” (Programmable Logic Controller)
Presented By:
ROHIT GUPTA

2. What is 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

3. History of PLC First Programmable Logic Controllers was designed
and developed by Modicon as a relay replacer
for General Motors.
The first PLC, model name 084, was invented by
Morley in 1969 who is considered to be the "father" of
the PLC.
The first commercial successful PLC, the 184, was
introduced in 1973 which was designed by Michael
Greenberg.

4. PLC Hardware 1) Central Processing Unit (CPU) 2) Memory 3) Input modules ) Output modules 5) Power supply 6) I/O Bus

5. General PLC architecture
Programming device
Power Supply
CPU
Memory
I/O Bus
I/O System Module
Output Devices
Input Devices

6. PLC operation sequence
1) Self test: Testing of its own hardware and software
for faults.
2)Input scan: If there are no problems, PLC will copy all
the inputs and copy their values into memory.
3)Logic solve/scan: Using inputs, the ladder logic program is solved once and outputs are updated.
4)Output scan: While solving logic the output values
are updated only in memory when ladder scan is done,
the outputs will be updated using temporary values in
memory.

7. Block diagram of a PLC
LEDs
Outputs
Inputs

8. Programming Languages of PLC
IEC currently defines five programming languages for PLCs
1) Functional Block Diagram
2) Ladder Logic
3) Structured Text similar to the Pascal Programming
language
4) Instruction List similar to Assembly language
5) Sequential Function Chart

9. Ladder Logic The ladder logic is the oldest programming
language for PLC.
It is well suited to express Combinational
logic
The main ladder logic symbols represent the
elements:
make contact
break contact
relay coil

10. Basic gates A Y Y B A B AAND Gate OR Gate A B Logic(Y) OFF ON A B

11. NOR Gate
NAND Gate A B
Logic(Y)
OFF ON A B
Logic(Y)
OFF ON A Y A B Y B

12. Ladder Logic Program for Start/Stop of Motor :
Programming Example:
Ladder Logic Program for Start/Stop of Motor : X1 X2 Y1 Y1

13. Programming PLC:

14. Starting of Motor:

15. Continuous Running of motor when Start Button is released:

16. To Stop the Motor :

17. Advantages of PLCs: 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.
Ease of maintenance /troubleshooting.
Reduced space.
Energy saving.

18. Disadvantages of PLCs PLC devices are proprietary.
Fixed Circuit Operations.
PLCs manufacturers offer only closed architectures.

19. Applications: 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
5) Materials handling
6)Machine tools
7)Conveyer system etc.

20. Thank You