PLC

1. PLC ( Programable Logic
Controllers)
KHADIJAH MUSHTAQ (CIIT/FA14-BEE-048/ATK)
HIKMATULLAH (CIIT/FA1X-BEE-0XX/ATK)
TALHA NADEEM (CIIT/FA14-BEE-007/ATK)

2. Topical Layout
• Types and Purpose of Control
• Evolution of logic controller devices
• Leading PLC manufacturers around the world
• PLC architecture
• PLC operation
• Criteria for PLC selection
• Advantages of PLC

3. Types of Control
• Temporal -- control based in time
• State -- control based in state level
• Hybrid – both temporal and state

4. Purpose of Control
• On-Off Control
• Sequential Control
• Feedback Control
• Motion Control

5. Evolution of logic controller devices
• Relay controllers
• Semi-conductor logic controllers
• Programmable Logic Controllers (PLC)

6. RELAY CONTROLLERS
• Large dimensions
• Slow
• Noisy
• Requires a lot of energy to work
• Sensible for dirt

7. SEMI-CONDUCTOR
LOGIC CONTROLLERS
• Fast
• Small
• Reduced energy
• Silent
• Hard to adapt to another
controlling task

8. PROGRAMMABLE
LOGIC CONTROLLERS
(PLC)
• All advantages of the semi-
conductor logic controllers
• Easy to adapt (re-programming)
• Real-time working
• Minimal maintenance
• Low costs

9. PLC Vs. Microcontrollers
• Dissimilar to Microcontrollers:
• Intended for Industrial Applications
• I/O Designed to interface with Control Relays
• Emphasis on Maximum Reliability

10. Areas of application
• Water handling
• Agriculture
• Traffic control
• Food industry
• Manufacturing / Machining
• Mining

11. Leading PLC manufacturers (US)
• Allen Bradley
• Gould Modicon
• Texas Instruments
• General Electric
• Westinghouse
• Cutter Hammer
• Square D

12. Leading PLC manufacturers (EU)
• Siemens
• Klockner & Mouller
• Festo
• Telemechanique

13. Leading PLC manufacturers (Japan)
• Toshiba
• Omron
• Fanuc
• Mitsubishi

14. Criteria for PLC selection
• Number of logical inputs and outputs.
• Memory
• Number of special I/O modules
• Scan Time
• Communications
• Software

15. PLC architecture
Program
memory
Data
memory
Processor
Communication
unit
Input
module
Programming
unit
Output
module
System
memory

16. Processor
• The main function of the microprocessor is to analyze data coming
from field sensors through input modules, make decisions based on
the user’s defined control program and return signal back through
output modules to the field devices.
• Field sensors: switches, flow, level, pressure, temp. transmitters,
etc. Field output devices: motors, valves, solenoids, lamps, or
audible devices.

17. Memory
• System memory
• ROM (Read Only Memory)
• PROM (Programmable Read Only Memory)
• EPROM (Erasable Programmable Read Only Memory)
• EEPROM (Electric Erasable Programmable ROM)
• Program/Data memory
• RAM (Random Access Memory)

18. Input/Output modules
• The I/O interface section of a PLC connects it to external field
devices.
• The main purpose of the I/O interface is to condition the various
signals received from or sent to the external input and output
devices.
• Input modules converts signals from discrete or analog input
devices to logic levels acceptable to PLC’s processor.
• Output modules converts signal from the processor to levels
capable of driving the connected discrete or analog output devices.

19. Input Modules
DC INPUT MODULE
STANDARD DIGITAL INPUT SIGNALS: 24V
AC INPUT MODULE
STANDARD ANALOG INPUT SIGNALS: 0-
10V
Current
limiting
resistor
Opto-
isolator
Buffer,
filter,
hysteresis
circuits
DC input Processor
Used to
drop the
voltage to
logic level
Prevents voltage transients
from damagigng the
processor.
Helps to reduce the effects of
electrical noise.
Rectifier,
Resistor
Network
Opto-
isolator
Buffer,
filter,
hysteresis
circuits
AC input Processor
Converts the AC
input to DC and
drops the voltage
to logic level
Prevents voltage transients from
damagigng the processor.
Helps to redice the effects of
electrical noise.

20. Output module
Standard Analog Output signals: 4-20mA; 0-5V; 0-10V
TTL
circuits
Opto-
isolator
AplifierProcessor Output

21. Communication unit
Manages the communication between the PLC and
• the controlled process,
• an other PLC,
• a PC,
• different peripheries.
Used ports:
• Serial (RS 232, RS 422, RS 485)
• Ethernet

22. PLC Operation Scheme
Power-on the PLC
Clear the output table
Input links Input table update
PLC program
Instruction 1
Instruction 2
…
Instruction n
Output table update
Output links
…
…
Input signals
Output signals

23. Advantages of PLC
• The less cable the less cost.
• Higher reliability and performance.
• Smaller installation and service costs.
• The ability of teleprogramming and telemonitoring.
• Changing resident PLC programs - uploading/downloading from a
supervisory controller (Laptop or desktop computer).
• Forcing I/O points and memory elements from a remote terminal.

24. Reference
• Skvarenina/DeWitt, Electrical Power and Controls, Pearson-Prentice
Hall, 2004

25. “Don’t Make Excuses,
Make Improvements.”
- Tyra Banks
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