plc ( programable logic controllers)
TRANSCRIPT
PLC ( Programable Logic Controllers)
KHADIJAH MUSHTAQ (CIIT/FA14-BEE-048/ATK)HIKMATULLAH (CIIT/FA1X-BEE-0XX/ATK)TALHA NADEEM (CIIT/FA14-BEE-007/ATK)
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
Types of Control• Temporal -- control based in time
• State -- control based in state level
• Hybrid – both temporal and state
Purpose of Control
• On-Off Control• Sequential Control• Feedback Control• Motion Control
Evolution of logic controller devices• Relay controllers
• Semi-conductor logic controllers
• Programmable Logic Controllers (PLC)
RELAY CONTROLLERS
• Large dimensions
• Slow
• Noisy
• Requires a lot of energy to work
• Sensible for dirt
SEMI-CONDUCTOR LOGIC CONTROLLERS
• Fast
• Small
• Reduced energy
• Silent
• Hard to adapt to another controlling task
PROGRAMMABLE LOGIC CONTROLLERS (PLC)• All advantages of the semi-
conductor logic controllers
• Easy to adapt (re-programming)
• Real-time working
• Minimal maintenance
• Low costs
PLC Vs. Microcontrollers
• Dissimilar to Microcontrollers:• Intended for Industrial Applications• I/O Designed to interface with Control Relays• Emphasis on Maximum Reliability
Areas of application• Water handling
• Agriculture
• Traffic control
• Food industry
• Manufacturing / Machining
• Mining
Leading PLC manufacturers (US)• Allen Bradley
• Gould Modicon
• Texas Instruments
• General Electric
• Westinghouse
• Cutter Hammer
• Square D
Leading PLC manufacturers (EU)• Siemens
• Klockner & Mouller
• Festo
• Telemechanique
Leading PLC manufacturers (Japan)• Toshiba
• Omron
• Fanuc
• Mitsubishi
Criteria for PLC selection• Number of logical inputs and outputs.
• Memory
• Number of special I/O modules
• Scan Time
• Communications
• Software
PLC architecture
Program memory
Data memory
Processor
Communicationunit
Input module
Programming unit
Output module
Systemmemory
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.
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)
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.
Input Modules
DC INPUT MODULESTANDARD DIGITAL INPUT S IGNALS: 24V
AC INPUT MODULESTAN DARD A NA LOG I NPUT S IGN A LS : 0 -10V
Current limiting resistor
Opto-isolator
Buffer, filter,
hysteresiscircuits
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,
hysteresiscircuits
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.
Output module
Standard Analog Output signals: 4-20mA; 0-5V; 0-10V
TTL circuits
Opto-isolator
AplifierProcessor Output
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
PLC Operation Scheme
Power-on the PLC
Clear the output table
Input links Input table update
PLC program
Instruction 1Instruction 2…Instruction n
Output table update
Output links
…
…
Input signals
Output signals
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.
Reference• Skvarenina/DeWitt, Electrical Power and Controls, Pearson-Prentice
Hall, 2004
“Don’t Make Excuses,Make Improvements.”- Tyra Banks
THANKYOU