1. PROGRAMMABLE
LOGIC CONTROLLER
SOFCON INDIA PVT. LTD.
MENTOR: SHEKHAR MAURYA
PROF. S.K.PAHUJA 09106068
INSTRUMENTATION &
CONTROL

2. PLC
 The PLC is an assembly of solid state
digital logic elements design to make
logical decisions and provide outputs.
 PLC is programmed interface between
input sensor &output device.
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3. Programmable Logic
Controllers
Advantages of PLC :
 They are fast and designed for the rugged industrial
environment.
 They are attractive on Cost-Per-Point Basis.
 These Devices are less Proprietary ( E.g.. Using Open
Bus Interface.)
 These Systems are upgraded more Capabilities with
dedicated PID and Ethernet Modules.
Disadvantages of PLC :
 PLC one time cost is high
 To maximize PLC performance a number of IO Modules
to be added.
 PLC hold only one copy DEKprogram.
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4. P L C Components(Hardware)
 CentralProcessing Unit (CPU)
 Input Modules
 Output Modules
 Power Supply
 Bus system
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5. Advantage of PLC Over Relay
RELAY PLC
1-More wiring 1-Less wiring
2-Changes difficult 2-Changes easy
3-More power 3-Low power
4-More maintenance 4-Solid state
reliability
5-Difficult to expand 3113 -Easy to expand
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6. PLC Cycle
 Sense the Input
 Process the Logic
 Give Output
Inputs CPU Outputs
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7. Ladder Diagram
 Ladder diagrams are specialized schematics commonly used to
document industrial control logic systems.
 It is a language or a method to create a program. The first PLCs
were programmed with a technique that was based on relay
logic wiring schematics.
 Basic concept of this diagram is similar to the electrical wiring.
However in ladder logic, the symbol has changed and been
standardized.
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8. Ladder Diagram cont..
 Type of graphic language automatic control systems.
 A drawing program of a switching circuit.
 Called "ladder" diagrams because they resemble a
ladder, with two vertical lines representing the power
trails (supply power) and circuits are connected in
horizontal lines called rungs. Connection between the
element in the rung called link.
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9. Ladder Diagram Operational
Principle
 Referring to figure below, between these two rails, a horizontal
straight line was drawn with two symbols. These two symbols refer to
the input and output devices, which are used in the actual
process/system.
 On the left, we put all kinds of input. While on the right, we place all
types of the outputs.
 Once we complete one line of the program it seems like a ladder. This
horizontal line which places the input and output make one rung.
+24V -0V
Input Interface Output
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10. Ladder Diagram Symbols
 Ladder diagram uses standard symbols to represent the
circuit components and functions found in a control
system.
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11. Normally Open Schematics
(NO)-Input Schematics
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12. Normally Closed Schematics
(NC)-Input Schematics
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13. Output Schematics
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14. Logic Function
 There are 5 logic functions can be
developed by combination of switches
1. AND
2. OR
3. NOR
4. NAND
5. EX-OR (XOR)
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15. Logic Function…cont
1. AND logic
coils is not energized
unless both switch A
and B closed. Fig.
(b) represent for PLC
input.
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16. Logic Function…cont - AND
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17. Logic Function…cont
2. OR logic
Coils is not energized
until either A or B
closed
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18. Logic Function…cont –
OR
 DeMorgan's Theorem would predict:
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19. Logic Function…cont
3. NOR logic
Since there has to
be an output when
neither A nor B
have an input, and
when there is an
input either A or B.
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20. Logic Function…cont -
NOR
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21. Logic Function…cont
4. NAND logic
There is no output
when both A and B
have an input
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22. Logic Function…cont -
NAND
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23. Logic Function…cont - NOT
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24. Logic Function…cont
5. XOR logic
There is no output
when both input 1
and 2 given.
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25. Combination of AND, OR, and
inverter (NOT) gates
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26. Control Circuit
Start stop circuit
-PB is pressed, output IR is activated
-IR contact will closed
-When PB is depressed, the output IR is still
activated since current can go through contact IR
unless is disturbed by stop button.
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27. Vibrating/Jog circuit
-When, PB is pressed, output IR is activated.
-When, PB is pressed, output IR is activated.
-But after several microsecond, the normally closed IR is
-But after several microsecond, the normally closed IR is
open then will stop the output IR.
open then will stop the output IR.
-This applicable to move an object which need to locate
-This applicable to move an object which need to locate
at precise location.
at precise location.
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