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Week 10 1_introduction_to_plc

Date post: 20-Jan-2015
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hydraulic subtopic
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Page 1: Week 10 1_introduction_to_plc
Page 2: Week 10 1_introduction_to_plc

Industrial computer in which the hardware and software have been specifically adapted to the industrial environment

Page 3: Week 10 1_introduction_to_plc

Inp

ut

Power Supply

CPU

Memory

Ou

tpu

t Switches

Sensors

Etc.

Valves

Motor starter

Lights

Etc.

Programming device

(PC, PLC, etc.)

Page 4: Week 10 1_introduction_to_plc

Contains one or more microprocessors – brain for PLC

Same type of microprocessor in microcomputer -except PLC microprocessor accommodate ladder logic instead of other languages

Functions – executes the tasks, manages memory, monitors input, evaluate logic (ladder diagram) & turn on appropriate output.

Page 5: Week 10 1_introduction_to_plc

ROM

◦ Operating System (OS) is burnt into ROM by manufacturer

◦ Contains OS control function (software..e.g. Windows in PC)

◦ Nonvolatile memory-when the electricity shut off, the memory is retained

◦ Users cannot change ROM

Page 6: Week 10 1_introduction_to_plc

RAM

◦ User memory

◦ User can read or write program to RAM

◦ Volatile – when electricity shut off, the data in memory lost

◦ Use battery to avoid ‘memory loss’

Page 7: Week 10 1_introduction_to_plc

Device that are used to write the program and trouble shoot the PLC

Example

◦ PC, handheld programmers, microcomputers

Page 8: Week 10 1_introduction_to_plc

Power Supply

To supply power for CPU

Most PLCs operate on 115 V AC

Page 9: Week 10 1_introduction_to_plc

Performs 2 tasks – taking input from outside world & protecting CPU from outside world

Convert real-world logic (eg. 250 V AC input module) to require logic level by CPU (eg. Low-level DC signal for CPU)

Input devices – switches, sensors, etc.

Page 10: Week 10 1_introduction_to_plc

Provide connection to real-world output

Eg. – motor starters, lights, coils, valves etc.

Page 11: Week 10 1_introduction_to_plc

Ladder Logic

◦ Symbolic representation of electrical circuit

◦ Symbols in ladder logic is divided into contacts (input) and coils (output)

Page 12: Week 10 1_introduction_to_plc
Page 13: Week 10 1_introduction_to_plc

Most input to PLC are either on (true) or off (false)

Input – sensors and switches

Common symbols

◦Normally open--------

◦Normally closed------

Page 14: Week 10 1_introduction_to_plc

Coils are output symbols

Real output device – motor, light, pump, counter, timer, relay

PLC examine contact (input) in ladder and turn the coil (output) on or off

Coil symbol -------

Page 15: Week 10 1_introduction_to_plc

Problem: Draw a ladder diagram for a bell circuit. When a switch is pressed, the bell will ring

Page 16: Week 10 1_introduction_to_plc

Modify the diagram, so that when the switch is pressed once and released, the bell is ringing continuously

Page 17: Week 10 1_introduction_to_plc

Add another button to stop bell ringing

Page 18: Week 10 1_introduction_to_plc

A drill press machine only works if there is a part present and the operator has one hand on each start switches (2 start switches)

Page 19: Week 10 1_introduction_to_plc

Using single solenoid with spring return & 2 sensor for each cylinder

Page 20: Week 10 1_introduction_to_plc

Using single solenoid with spring return & 1 sensor for each cylinder

Page 21: Week 10 1_introduction_to_plc

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