PLC is a multipurpose clock-driven memory-based electronic device which is also known as a specialized industrial computer which deals with different level of complexity and control system.

1. .

2. University of Kerbala
College Of Engineering
Electrical & Electronic Engineering Department
PLC ‫وتطبيقات‬ ‫أساسيات‬ ‫حول‬ ‫تدريبية‬ ‫دورة‬
Basics and Applications of Programmable Logic
Controller (PLC)
By
Assist Prof. Dr. Ali A. Altahir
Presenter: Uday A. Alhamdany
Engineer: Ahmed Mohsen
2020 – 2021
.

3. Automation?
Automation is the use of control systems and
information technologies to reduce the need for
human work in the production of goods and services.

4. Need of Automation?
To get maximum production in minimum time with
minimum cost and reduce human effort

5. Advantages of Automation
• Replacing humans in tasks done in dangerous
environments (i.e. fire, space, volcanoes).
• Performing tasks that are beyond human capabilities
of size, weight, speed)
• Economy improvement.

6. Disadvantages of Automation
• Unemployment.
• Unpredictable development costs.
• High initial cost.
• Lack of intelligence

7. Engineering Tools
• PLC (Programmable Logic Controller)
• HMI (Human Machine Interface)

8. Programmable Logic Controller
(Programmable Logic Controller): PLC is a multipurpose clock
driven memory based electronic device which is also known as
specialized industrial computer which deals with different level
of complexity and control system.

9. Advantages of PLC
• Correcting Errors & implementing changes.
• Testing
• Large quantity of contacts.
• Reliability and maintainability.
• Less wiring.
• Easier and faster to make changes.
• Trouble shooting aids make programming easier and
reduce downFlexibility
• time.
• Reliable components make these likely to operate for years
before failure.

10. FUNCTIONS OF CONTROLLERS
1) On-off control
2) Sequential control of logical systems
3) Feedback control
4) Motion control of dynamic systems.

11. Interlocking
• An arrangement of signals and signal appliances so
interconnected that their movements must succeed each
other in proper sequence.

12. CONTROL DEVICES
1) Mechanical control - cam, governor, etc...
2) Pneumatic control - compressed air, valves, etc...
3) Electromechanical control - switches, relays, timers,
counters, etc…
4) Electronics control - similar to electromechanical
control, except uses electronic switches.
5) Computer control.

13. i. Compact PLC
ii. Modular PLC
iii. PLC Plug-in Card
Types of PLC based on Construction

14. Types of PLC based on Construction
i. Compact PLC:
Compact PLC – MELSEC FX3U
Figure 1: Compact PLC

15. ii. Modular PLC
Figure 2: Modular PLC

16. iii. PLC Plug-in Card
Figure 3: Plug-in Card PLC

17. • Small :
- It covers units up to 128 I/O’s and memories up to 2 Kbytes.
- Capable of providing simple to advance levels or machine
controls.
• Medium :
- Have up to 2048 I/O’s and memories up to 32 Kbytes.
• Large :
- The most sophisticated units of the PLC family. They have up to
8192 I/O and memories up to 750 Kbytes.
- Can control individual production processes or entire plant.
PLC Size

18. Leading Brands Of PLC
AMERICAN 1. Allen Bradley
2. Gould Modicon
3. Texas Instruments
4. General Electric
5. Westinghouse
6. Cutter Hammer
7. Square D
EUROPEAN 1. Siemens
2. Klockner & Mouller
3. Festo
4. Telemechanique

19. Leading Brands Of PLC
JAPANESE 1. Omron
2. Toshiba
3. Fanuc
4. Mitsubishi

20. 20
Allen-Bradley PLC’s
• Below are Allen-Bradley PLC’s
• Note that AB is part of the Rockwell Automation, a global
leading Automation giant.

21. Eng. R. L. Nkumbwa @ CBU 2010 21

22. 22
Siemens Simatic PLC’s
• Below are Siemens Simantic PLCs

23. Eng. R. L. Nkumbwa @ CBU 2010 23

24. PLC ARCHITECTURE
A typical PLC

25. PLC ARCHITECTURE
Programmable controllers replace most of the relay panel
wiring by software programming.
Processor
I/O
Modules
Memory
Power
Supply
Program
Loader
Printer
Cassette
Loader
EPROM
Loader
Switches
Machines
Peripherals External Devices
PC

26. System components of a PLC
PLC Program
HW

27. System components of a PLC
PLC Program
HW
SW

28. System components of a PLC
PLC Program
HW
SW PLC

29. PLC and Field
PLC Program
HW
SW PLC
FIELD

30. PLC, Field and Controlled system
PLC Program
HW
SW PLC
FIELD
CONTROLLED PROCESS or CONTROLLED MACHINE

31. Parts of PLC
• Processor
• Memory
• Input
• Output
• Power Supply

32. Processor
Processor converts any given input into
valuable output and memory is used for
functioning and storage of programs.

33. Memory Unit
For storage of programs.
The user’s ladder logic program, the state of I/O in the memory of PLC.
The main program and the other programs necessary for the operation of
PLC.
The organization of the data and information in the memory is called
memory map.
2 types of Memory
RAM
ROM

34. TYPES OF MEMORY:
RAM
Random Access Memory
ROM
Read Only Memory (read)
This memory can be read from
and written to.
This memory can be read only
Storing all user’s programs Storing all system’s program
Entire contents will be lost if power
is switched off.
Memory content remain when the
power is switched off.

35. I/O Module
• 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.

36. Isolated Inputs
The inputs of the PLC are various sensor which
are used to sense the condition at the remote
location.These sensors are isolated with PLC.

37. Level SW
Flow SW
Thumbwheel SW
Limit Switch
Push Button

38. I/O Module
DC INPUT MODULE
OPTO-
ISOLATOR
IS NEEDED TO:
• Prevent voltage
transients from
damaging the
processor.
•Helps reduce the
effects of electrical
noise
Current
Limiting
Resistor
FROM
INPUT
DEVICE
USE TO
DROP THE
VOLTAGE
TO LOGIC
LEVEL
Buffer,
Filter,
hysteresis
Circuits
TO
PROCESSOR

39. 39
I/O Module
AC INPUT MODULE
OPTO-
ISOLATOR
IS NEEDED TO:
• Prevent voltage
transients from
damaging the
processor.
•Helps reduce the
effects of electrical
noise
Rectifier,
Resistor
Network
FROM
INPUT
DEVICE
CONVERTS THE AC
INPUT TO DC AND
DROPS THE VOLTAGE
TO LOGIC LEVEL
Buffer,
Filter,
Hysteresis
Circuits
TO
PROCESSOR

40. Isolated output
The output terminals module has terminals to
which output signals are sent to activate relay,
motors and displays.

41. Motor
Solenoid
LED Display
Heater Coil
Lamp

42. I/O Module
DC / AC OUTPUT MODULE
OPTO-
ISOLATOR
IS NEEDED TO:
• Prevent voltage
transients from
damaging the
processor.
•Helps reduce the
effects of electrical
noise
FROM
PROCESSOR
TTL
Circuits
Amplifier
RELAY
TRIAC
X’SISTOR
TO
OUTPUT
DEVICE

43. PLC
INPUTS
OUTPUTS
MOTOR
LAMP
CONTACTOR
PUSHBUTTONS

44. N.
O
C
L2 L1
L1
L2
OUTPUT MODULE
WIRING
MOTOR
CONTACTOR
O:4
0
CONTACTOR
LADDER PROGRAM
L1 L2
FIELD WIRING
•SOLENOID
•VALVES
•LAMP
•BUZZER

45. 45
OFF
Logic 0
IN
PLC
Input
Module
24 V dc
On
Logic 1
IN
PLC
Input
Module
24 V dc

46. 46
IN
PLC
Analog
Input
Module
Tank
Level Transmitter
An analog input is an input signal that has a continuous
signal. Typical inputs may vary from 0 to 20mA, 4 to 20mA
or 0 to10V. Below, a level transmitter monitors the level of
liquid in the tank. Depending on the level Tx, the signal to the
PLC can either increase or decrease as the level increases
or decreases.
Analog Input

47. 47
OUT
PLC
Digital
Output
Module
Lamp
A discrete output is either in an ON or OFF condition. Solenoids,
contactors coils, lamps are example of devices connected to the
Discrete or digital outputs. Below, the lamp can be turned ON or
OFF by the PLC output it is connected to.
Digital Output

48. OUT
PLC
Analog
Output
Module
An analog output is an output signal that has a continuous
signal. Typical outputs may vary from 0 to 20mA, 4 to 20mA
or 0 to10V.
Analog Output
E
P
Pneumatic control valve
Supply air
Electric to pneumatic transducer
0 to 10V

49. Analog I/O
Circuits of this type sense or drive analog signals.
Analog inputs come from devices, such as thermocouples,
strain gages, or pressure sensors, that provide a signal
voltage or current that is derived from the process variable.
Standard Analog Input signals: 4-20mA; 0-10V
Analog outputs can be used to drive devices such as
voltmeters, X-Y recorders, servomotor drives, and valves
through the use of transducers.
Standard Analog Output signals: 4-20mA; 0-5V; 0-10V

50. Power Supply
• The electrical supply that converts the alternating current line
voltage to various operational DC values. In this process the
power supply filters and regulates the Dc voltages to ensure
the computer operation.

51. Monitor
It provides a visual status of PLC.It may have LCD screen
or LED indicator.

52. Communication Port
It is used to connect the PLC with computer.A
communication cable is used for this purpose.

53. PLC Communications
Common Uses of PLC Communications Ports
 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.
 Linking a PLC into a control hierarchy containing several
sizes of PLC and computer.
Monitoring data and alarms, etc. via printers or Operator
Interface Units (OIUs).

54. PLC Communications
Serial Communications
PLC communications facilities normally provides serial
transmission of information.
Common Standards
RS 232
 Used in short-distance computer communications, with the
majority of computer hardware and peripherals.
 Has a maximum effective distance of approx. 30 m at
9600 baud.

55. PLC Communications
Local Area Network (LAN)
Local Area Network provides a physical link between all
devices plus providing overall data exchange management or
protocol, ensuring that each device can “talk” to other
machines and understand data received from them.
LANs provide the common, high-speed data communications
bus which interconnects any or all devices within the local
area.
LANs are commonly used in business applications to allow
several users to share costly software packages and peripheral
equipment such as printers and hard disk storage.

56. PLC Communications
RS 422 / RS 485
 Used for longer-distance links, often between several
PCs in a distributed system. RS 485 can have a
maximum distance of about 1000 meters.

57. PLC Communications
Programmable Controllers and Networks
Dedicated Network System of Different Manufacturers
Manufacturer Network
Allen-Bradley Data Highway
Gould Modicon Modbus
General Electric GE Net Factory LAN
Mitsubishi Melsec-NET
Square D SY/NET
Texas Instruments TIWAY

58. TYPES OF SWITCHES
1. Basic switch, operated by a mechanical level,
2. Push-button switch,
3. Slide switch,
4. Thumbwheel switch,
5. Limit switch,
6. Proximity switch, and
7. Photoelectric switch.
RATING: voltage, current

59. 60
Discrete Input
A discrete input also referred as digital input is an input that is
either ON or OFF are connected to the PLC digital input. In the
ON condition it is referred to as logic 1 or a logic high and in the
OFF condition maybe referred to as logic o or logic low.
Normally Open Pushbutton
Normally Closed Pushbutton
Normally Open switch
Normally Closed switch
Normally Open contact
Normally closed contact

60. RELAYS
A switch whose operation is activated by an electromagnet is
called a "relay"
contact
coil
input
Relay coil Output contact

61. COUNTER
Digital counters output in the form of a relay contact
when a preassigned count value is reached.
Register
Accumulator
contact
input
reset
output
Input
Reset
Output
Count 0 1 2 3 4 5 0 1
5

62. TIMER
A timer consists of an internal clock, a count value
register, and an accumulator. It is used for or some
timing purpose.
Clock
Accumulator
contact
reset
output
Register
Contact
Time 5 seconds.
Clock
Reset
Output
Count 1 2 3 4
0 5

63. Selecting a PLC
Criteria
• Number of logical inputs and outputs.
• Memory
• Number of special I/O modules
• Scan Time
• Communications
• Software

64. A Detailed Design Process
1. Understand the process
2. Hardware/software selection
3. Develop ladder logic
4. Determine scan times and memory requirements

65. Specifications
Several factors are used for evaluating the quality and
performance of programmable controllers when selecting a
unit for a particular application. These are listed below.
NUMBER OF I /O PORTS
This specifies the number of I/O devices that can be
connected to the controller. There should be sufficient I/O
ports to meet present requirements with enough spares to
provide for moderate future expansion.

66. Specifications
OUTPUT-PORT POWER RATINGS
Each output port should be capable of supplying sufficient
voltage and current to drive the output peripheral connected
to it.
SCAN TIME
This is the speed at which the controller executes the relay-
ladder logic program. This variable is usually specified as the
scan time per 1000 logic nodes and typically ranges from 1 to
200 milliseconds.

67. Specifications
MEMORY CAPACITY
The amount of memory required for a particular application is
related to the length of the program and the complexity of the
control system. Simple applications having just a few relays
do not require significant amount of memory. Program length
tend to expand after the system have been used for a while.
It is advantageous to a acquire a controller that has more
memory than is presently needed.

68. Software Used
The software used for PLC programming is RSLogix 500.
• RSLogix Micro software is a 32-bitWindows ladder logic
programming package for the MicroLogix processors.

69. Examples of PLC Programming Software:
1. Allen-Bradley – Rockwell Software RSLogix500
2. Modicon - Modsoft
3. Omron - Syswin
4. GE-Fanuc Series 6 – LogicMaster6
5. Square D- PowerLogic
6. Texas Instruments – Simatic
6. Telemecanique – Modicon TSX Micro

70. Language Used
• The language used for PLC programming is Ladder logic.
• Ladder logic is a programming language that represents
a program by a graphical diagram based on the circuit
diagrams of relay logic hardware.

71. SCAN
begin
Input
Output
Resolve
logic
Idle
A PLC resolves the logic of a ladder diagram (program) rung by rung,
from the top to the bottom. Usually, all the outputs are updated
based on the status of the internal registers. Then the input states
are checked and the corresponding input registers are updated. Only
after the I/Os have been resolved, is the program then executed.
This process is run in a endless cycle. The time it takes to finish one
cycle is called the scan time.
Scan cycle

72. The scan time is a function of:
• The speed of the processor module
• The length of the ladder program
• The type of instructions executed
• The actual ladder true/false conditions
The PLC computes the scan time each
time the END instruction is executed.
Typical scan time data include the
maximum scan time and the last scan time.

73. Scan process applied to a single rung program.

74. Vertical versus horizontal scan patterns.

75. LADDER DIAGRAM
A ladder diagram (also called contact symbology) is a means
of graphically representing the logic required in a relay logic
system.
A
R1
PB1 PB2
R1
R1
start emergency stop
Rail
Rung

76. PLC programming language refers to the method by which the user
communicates information to the PLC.
Standard PLC programming languages

77. PLC: example 1
Programming language: LADDER LOGIC
IF THEN

78. PLC INSTRUCTIONS
1) Relay,
2)Timer and counter,
3) Program control,
4) Arithmetic,
5) Data manipulation,
6) Data transfer, and
7) Others, such as sequencers.

79. LOGIC STATES
ON :TRUE, contact closure, energize, etc.
OFF: FALSE, contact open , de-energize, etc.
(In the notes we use the symbol "~" to represent
negation. AND and OR are logic operators. )
Do not confuse the internal relay and program with the external
switch and relay. Internal symbols are used for programming.
External devices provide actual interface.

80. AND and OR LOGIC
PB1 R1
PB2
R2
R1 = PB1.AND.PB2
R2 = PB2.AND.~PB4
PB3 PB4
PB1 R1
PB2
R1 = PB1 .OR. PB2
AND
OR

81. COMBINED AND & OR
R1 = PB1 .OR. (PB2 .AND. PB3)
PB1 R1
PB2 pb3

82. Instruction list programming language consists of a series
of instructions that refer to the basic AND, OR, and NOT
logic gate functions.
Hardwired
relay control
circuit
Equivalent
instruction
list program

83. XOR Logic
A xor B:
(A is ON AND B is OFF) OR (A is OFF AND B is ON)

84. RELAYS
A Relay consists of two parts, the coil and the contact(s).
Contacts:
a. Normally open -| |-
b. Normally closed -|/|-
c. Off-on transitional -||-
d. On-off transitional -| |-
Coil:
a. Energize Coil -( )-
b. De-energize -(/)-
c. Latch -(L)-
d. Unlatch -(U)-
( )

85. TIMERS AND COUNTERS
Timers:
a. Retentive on delay (RTO)
b. Retentive off delay (RTF)
c. Reset (RST)
Counter:
a. Counter up (CTU)
b. Counter down (CTD)
c. Counter reset (CTR)
RTO counting stop counting
resume
RTF stop counting stop
True False True
Input
RTO reach PR value, output ON
RTF reach PR value, output OFF
PR value in 0.1 second

86. SEQUENCER
Sequencers are used with machines or processes involving
repeating operating cycles which can be segmented into
steps.
Output
Step A B C Dwell time
1 ON OFF OFF 5 sec.
2 ON ON OFF 10 sec.
3 OFF OFF ON 3 sec.
4 OFF ON OFF 9 sec.

87. Timer
Timers are output instructions that let you
control operations based on time or
number of events.

88. Types of timer
There are three types of timers:
1. TON (Delay turning on an output).
2. TOFF (Delay turning off an output).
3. RTO (Time an event retentively).

89. TONTimer

91. DescriptionTONTimer
As soon as the input button is switches ON
The status ofTON timer is:
➢En=1(when the input switch is ON)
➢TT=1(ON during the hole timing)
➢DN=0(During the whole timing and DN=1
after completion of timing)

92. TOFFTimer

94. TOFFTimer
There are three outputs ofTOFF timer:
➢EN (Enable )
➢TT (timing)
➢DN (Done)

95. DescriptionTOFFTimer
When the input switch is ON theTOFF timer is OFF.TOFF
timer started as soon as the output button is pressed.
When the input switch is ON, the output of the timer is:
➢EN =1
➢TT =0
➢DN =1

96. RTOTimer

98. Description of RTO
RTO stands for retentive timer. It functioning is same as of the
TON timer. But it retain the value even after the stop button
is pressed.

99. Ladder Logic: Timers
Solenoid actuated door-lock
Solenoid ON for 5 sec, then OFF
Solenoid ON ➔ Door unlocked
Solenoid actuated when:
(i) ON signal from number-pad outside door
(ii) ON signal from door-open switch inside door
While O:0/1 remains ON,
Timer COUNTS DOWN from PRESET
COUNT DOWN = 0 ➔ ( T4:1) set to ON

100. Ladder Logic: Timers
Solenoid actuated door-lock
Solenoid ON for 5 sec, then OFF
Solenoid ON ➔ Door unlocked
Solenoid actuated when:
(i) ON signal from number-pad outside door
(ii) ON signal from door-open switch inside door

101. Ladder Logic: counters
Count the number of occurrences of an event
Pallet loading in factory
After 10 parts arrive on conveyor, worker comes to load pallet
Examples:

102. Ladder Logic: counters
Pallet loading in factory After 4 parts arrive on conveyor:
STOP conveyor belt
turn ON the indicator light

103. References
• Computer Aided Manufacturing, Chang, Chang,T.C. and
Wysk, R. A. andWang, H.P., 3rd Edition, 2006.
• Automation ,Garry Johnston ,University of Newcastle,
Australia, 2010.