A presentation by Tirtha Paul Chowdhury on PLC basics. Tirtha Paul Chowdhury Electronics and Instrumentation Engineering 2017-2021 Techno India Saltlake, Kolkata

1. PLC
-Tirtha Paul Chowdhury

2. Content Layout:
• What ?
• Why ?
• History
• Major components
• What makes it work?
• Ladder logic
• FBD
• Explanation with a simple example
• Advantages and disadvantages
• Applications

3. WHAT?
0
50
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450
2014 2015 2016 2017 2018
Years
-> Programmable Logic Controller.
-> Computerized system for industrial control and automation.
WHY?
-> Hard-wired panels are time consuming to make as well to debug.
-> Demand for automation is increasing day by day.
Supply of industrial automation components (globally)

4. HISTORY
• Introduced in 1960’s
• First made by a company called Bedford Associates(MODICON)
• General Motors (U.S.A.) was the first to use PLC to replace hard wired
system with computer application.
• First used as a relay replacer for motor.

5. MAJOR COMPONENTS
Central Processor
Brain of PLC.
Operates at 5V DC.
Has secondary
memory.
I/O section
Input components
connected to input
section.
Output components
connected to output
section.
Input section filters
out noise from input
signals.
Power supply
Scales down supply
voltage.
Peripheral devices
Sensors, transducers,
push buttons etc.
Lamps, motors etc.

6. WHAT MAKES IT WORK?
• Input status signal coming from input device.
• Processor processes the data according to the programming
done and excites the output.
• PROGRAMMING LANGUAGES SUPPORTED BY PLC
1) GRAPHICAL:
• LADDER LOGIC
• FUNCTIONAL BLOCK DIAGRAM
2) TEXT BASED:
• STRUCTURED TEXT
• INSTRUCTION LIST

7. LADDER LOGIC
• Oldest programming language of
plc.
• Closely related to relay logic.
• Uses various circuit components like
NO contacts, NC contacts, timers,
counters etc.
• Read from top to bottom, left to
right.
Normally open Normally closed
POWER RAIL
NO CONTACT
RUNG
LAMP

8. FUNCTION BLOCK DIAGRAM
• It is a graphical language.
• Has certain blocks to which input is given and we get the output accordingly.
• All implementations are done within the block itself.
LOGICAL OR
INPUT OUTPUT
FUNCTION BLOCK

9. A PRACTICAL EXAMPLE HOW IT HELPS
• There is a bulb and a switch can control the state of that bulb.
• Now we want to blink that bulb.
• Either stand near the switch and on and off it at certain delay.
• Or do the whole wiring again for connecting a timer which should on and off the bulb at given time delay.
PLC COMES TO RESCUE HERE.
• Just connect a timer and modify the program used to get the output.

10. ADVANTAGES
• Much cheaper than traditional
wire system.
• More efficient.
• In case of any fault, debugging
is easy.
• For any change required in
output, minor modifications
needed in the program.
DISADVANTAGES
• We cannot mix and match
different parts of software
from different manufacturers.
• Most manufacturers offer
closed architecture.

11. APPLICATIONS
WHEREVER AUTOMATION IS REQUIRED,
PLC IS ALWAYS A CHOICE.
 Few examples are:
• Food processing industry
• Driving motors.
• Lighting lamps.
• Traffic signal controlling.
and many more…

12. THANK YOU!