Programmable logic controllers (PLCs) are solid-state industrial computer control systems that can store instructions to control machines and processes. PLCs are capable of controlling binary inputs and outputs, performing arithmetic and data manipulation, sequencing, timing, counting, and communication. Modern PLCs are modular, scalable, and programmable via simple programming methods to control industrial automation applications. PLCs use logic gates and binary concepts to read inputs, execute program instructions, and control outputs.

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2. DEFINITION
•Programmable logic controllers, also called
programmable controllers or PLCs, are solid-
state members of the computer family, using
integrated circuits instead of electromechanical
devices to implement control functions.
•They are capable of storing instructions, such
as sequencing, timing, counting, arithmetic,
data manipulation, and communication, to
control industrial machines and processes.
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4. Small modular PLC
courtesy ABB
courtesy Backmann
mounted on DIN-rail, 24V supply
cheaper (€5000)
not water-proof,
no ventilator
extensible by a parallel bus (flat cable or rail)
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5. Simple PLC
network binary inputs
analog inputs / outputs
binary outputs
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6. PLC in a cabinet
CPU1 CPU2
serial connections
redundant
field bus
connection inputs/outputs
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7. Global players
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8. • The control system had to be price competitive.
• It had to be capable of sustaining an industrial
environment.
• The I/O interfaces had to be easily replaceable.
• The controller had to be designed in modular form, so
that subassemblies could be removed easily for
replacement or repair.
• It needed the capability to pass data to a central system.
• The system had to be reusable.
• The method used to program it had to be simple. 8

9. TODAY’S PROGRAMMABLE CONTROLLERS
• Faster scan times.
• Small, low-cost.
• High-density input/output (I/O) systems.
• Intelligent, microprocessor-based.
• Mechanical design improvements.
• Special interfaces.
•Peripheral equipment has improved operator interface
techniques. 9

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11. Programmable controller block diagram
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12. Block diagram of major CPU components
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13. Graphic Representation of a Scan
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14. Input/Output Interface
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16. Personal Computer Used as a
Programming Devices
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17. Typical programmable controller applications
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19. PLC PRODUCT APPLICATION RANGES
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20. LADDER DIAGRAMS AND THE PLC
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23. Typical programmable controller
features and benefits.
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25. Programmable controller I/O connection diagram showing
no physical connections between the inputs and outputs.
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26. Remote I/O station installation
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27. EASE OF MAINTENANCE AND
TROUBLESHOOTING
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28. Failures in a PLC-based system
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29. A programming device being used to monitor
inputs and outputs, with highlighted contacts
indicating an ON condition.
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31. DECIMAL NUMBER SYSTEM
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32. BINARY NUMBER SYSTEM
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34. ASCII Code
representation of the character Z
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35. Binary Coded Decimal (BCD)
(Thumbwheel switch)
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36. Gray code
It is one of a series of cyclic codes known as reflected codes and
is suited primarily for position transducers
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38. Binary Concept Using Positive Logic
Binary Concept Using Negative Logic
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39. AND Gate
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40. OR Gate
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41. NOT Function
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47. Hardwired relay logic circuit
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48. ADDRESSES USED IN PLCS
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49. CONTACT SYMBOLS USED IN PLCS
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51. Multiple contacts
from a PLC output coil
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