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بسم الله الرحمن الرحيم. ( رب اشرح لي صدري ويسر لي امري واحلل عقدة من لساني يفقهوا قولي ). (وقل رب زدني علما ). The Islamic University Of Gaza Faculty Of Engineering Electrical Engineering Department Advanced Technical English. Programmable Logic controllers (PLC).

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بسم الله الرحمن الرحيم

( رب اشرح لي صدري ويسر لي امري واحلل عقدة من لساني يفقهوا قولي )

(وقل رب زدني علما )


The Islamic University Of Gaza

Faculty Of Engineering

Electrical Engineering Department

Advanced Technical English

Programmable Logic controllers (PLC)

BY : Marwan Hammouda 120030606

Sabri Mohammed Radi 120030171

To : Dr . Basil Hamad

functions of controllers
Functions of Controllers :
  • On-off control
  • Sequential control
  • Feedback control
  • Mation control
control devices
Control Devices:
  • Mechanical control
  • Pneumatic control
  • Electromechanical control
  • Electronic control
  • Computer control
programmable logic controllers plcs
Programmable Logic controllersPLCs
  • Were introduced in 1968
  • Were primarily intended to replace relay devices , so it is appropriate to be familiar with the components used in relay devices
plcs continue
PLCs (continue)
  • The National Electrical Manufacturing Associatioin (NEMA) defines the PLC as

“A digitally operating electronic apparatus which uses a programmable memory for the internal storage of instructions by implementing specific functions such as logic sequencing, timing, counting, and arithmetic to control, through digital or analog input/output modules, various types of machines or processes. The digital computer which is used to perform the functions of a programmable controller is considered to be within this scope. Excluded are drum and other similar mechanical sequencing controllers."

why is the plc
Why is the PLC ?
  • Cost effective for controlling complex systems.
  • Flexible and can be reapplied to control other systems quickly and easily
  • Computational abilities allow more sophisticated control.
  • Trouble shooting aids make programming easier and reduce downtime
  • Reliable components make these likely to operate for years before failure
plc components
PLC Components :
  • Processor : The processor (CPU) scans the status of the input peripheral , examines the control logic to see what action to take , and then excute the appropriate output response
  • Memory : the control program and the peripheral status are stored in the memory

ROM( Read Only Memory )

RAM (Random Access Memory),

PROM (Programmable Read Only Memory), EEPROM (Electric Erasable Programmable ROM),

EPROM (Erasable Programmable Read Only Memory), EAPROM (Electronically Alterable Programmable

plc components continue
PLC Components (continue)
  • Input/Output :

modular plug-in periphery

Ac voltage input and output

Dc voltage input and output

Low level analog input

High level analog input and output

Specail purpose modulas

  • Powre supply : Ac power
  • Peripherals : Hand-Held Programmer ( HHP)

CRT programmer

Operetor console



EPROM loader

Graphics processor

plc programming
PLC Programming
  • Ladder Diagram - most common
  • Structure Text Programming (ST)
  • Functional Block Programming (FB)
  • Instruction List (IL)
  • Sequential Function Chart (SFC)
ladder diagram
Ladder Diagram

A ladder diagram (also called contact symbology) is a means of graphically representing the logic required in a relay logic system.



plc ladder diagram instructions
1) Relay,

2) Timer and counter,

3) Program control,

4) Arithmetic,

5) Data manipulation,

6) Data transfer, and

7) Others, such as sequencers.

Hint : Relay , timer and counter instructions are the most fundemental because they correspond to what is on a ladder diagram and are avaliable on all PLCs so we limit our disscusion to them


A Relay consists of two parts, the coil and the contact(s).


a. Normally open -| |-

b. Normally closed -|/|-

c. Positive transition sensing -|P|-

d. Negative transition sensing -|N|-


a. Coil -( )-

b. negative coil -(/)-

c. Set Coil -(S)-

d. Reset Coil -(R)-




relay continue
Relay (continue)


e. Retentive memory Coil -(M)-

f. Set retentive memory Coil -(SM)-

g. Reset retentive memory Coil -(RM)-

h. Positive Transition-sensing Coil -(P)-

h. Negative Transition-sensing Coil -(N)-

(set coil latches the state, reset coil deenergize the set coil. retentive coil retain the state after power failure.)

timers and counters

a. Retentive on delay -(RTO)-

b. Retentive off delay -(RTF)-

c. Reset -(RST)-


a. Counter up -(CTU)-

b. Counter down -(CTD)-

c. Counter reset -(CTR)-



True False True

RTO counting stop counting


RTF stop counting stop

RTO reach PR value, output ON

RTF reach PR value, output OFF

PR value in 0.1 second