Pneumatic
and Hydraulic
Power
electronics
Switchgear,
Contactors
and Relays
Sensors
and Actors
Automation
Electronic
Controls and
Microcontroller
Closed Loop
Controller
Programmable
Logic Controller
Motors
Leading Brands of PLC
AMERICAN
EUROPEAN
JAPANESE
1 ALLEN BRADLEY
SIEMENS
2 GOULD MODICON
KLOCKNER & MOULLER OMRON
3 TEXAS INSTRUMENTS
FESTO
FANUC
4 GENERAL ELECTRIC
TELEMECHANIQUE
MITSUBISHI
5 WESTINGHOUSE
6 CUTTER HAMMER
7 SQUARE D
TOSHIBA
PLC Programing Software’s
1. Velocio Software
2. Siemens Software
3. Rockwell Automation (Allen-Bradley)
Software
4. Schneider Software
5. Mitsubishi Software
6. Modicon Software
7. Panasonic Software
8. Keyence Software
9. Telemecanique Software
10. Beckhoff Software
11. GE Software
12. Automation Direct Software
13. IDEC Software
14. Opto22 Software
15. Omron Software
16. Sirea Software
17. VIPA Software
18. Triangle Research International Software
19. SPLAT Software
20. Smart Software Solutions
21. LSIS Software
22. Control Microsystems Software
23. Teco Software
24. Unitronics Software
25. ABB Software
26. Horner APG Software
27. Crouzet Software
28. Xinje Software
29. Entertron Software
30. Delta Electronics Software
PLC Communications
1
2
3
4
5
6
Manufacturer
Allen-Bradley
Gould Modicon
General Electric
Mitsubishi
Square D
Texas Instruments
Network
Data Highway
Modbus
GE Net Factory LAN
Melsec-NET
SY/NET
TIWAY
PLC Acronyms
ASCII
BCD
CSA
DIO
EIA
EMI
HMI
IEC
IEEE
I/O
ISO
LL
LSB
MMI
MODICON
MSB
PID
RF
RIO
RTU
SCADA
American Standard Code for Information Interchange
Binary Coded Decimal
Canadian Standards Association
Distributed I/O
Electronic Industries Association
ElectroMagnetic Interference
Human Machine Interface
International Electrotechnical Commission
Institute of Electrical and Electronic Engineers
Input(s) and/or Output(s)
International Standards Organization
Ladder Logic
Least Significant Bit
Man Machine Interface
MOdular DIgital CONtoller
Most Significant Bit
Proportional Integral Derivative (feedback control)
Radio Frequency
Remote I/O
Remote Terminal Unit
Supervisory Control And Data Acquisition
Definition of PLC
According to NEMA standard ICS3-1978
• A digitally operating electronic apparatus
which uses a programming memory for the
internal
storage
of
instructions
for
implementing specific functions such as logic,
sequencing, timing, counting and arithmetic to
control through digital or analog modules,
various types of machines or process.
Areas of PLC Applications
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Annunciators
Injection Molding
Auto Insertion
Assembly
Bagging
Motor Winding
Baking
Oil Fields
Blending
Painting
Boring
Palletizers
Brewing
Pipelines
Calendaring
Polishing
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Casting
Reactors
Chemical Drilling
Robots
Color Mixing
Rolling
Compressors
Security Systems
Conveyors
Stretch Wrap
Cranes
Slitting
Crushing
Sorting
Cutting
Stackers
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Digesters
Stitching
Drilling
Stack Precipitators
Electronic Testing
Threading
Elevators
Tire Building
Engine Test Stands
Traffic Control
Extrusion
Textile Machine
Forging
Turbines
Generators
Turning
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Gluing
Weaving
Grinding
Web Handling
Heat Treating
Welding
Manufacturing/
Machining
Food / Beverage
Metals
Power
Mining
Petrochemical/Chemi
cal
PLC in industry
PLC in traffic light
Relating the PLC
Traditional system
PLC system
 control function is  Soft wiring
modified by physically  control function is modified
changing the wiring by just changing the control
between the devices
program inside the PLC
 This is costly and time  These changes are easy and
consuming endeavor
cheap
PLC and Computer
• A PLC and a computer both are electronic processor
unit. The architecture of a PLC’s CPU is basically same
as that of a general purpose computer; however,
some important characteristics set them apart.
• Unlike computer, PLCs are specifically designed to
survive the harsh conditions of the industrial
environment. A well-designed PLC can be placed in
an area with substantial amounts of electrical noise,
electromagnetic interference, mechanical vibration,
and noncondensing humidity.
Cont.…
• Distinction of PLCs is that their hardware and
software are designed for easy use by plant
electricians and technicians. The hardware
interfaces for connecting field devices are
actually part of the PLC itself and are easily
connected.
• The modular and self-diagnosing interface
circuits are able to pin point malfunctions and
moreover, are easily removed and replaced.
Cont.…
• Software programming uses conventional relay
ladder symbols, or other easily learned
languages, which are familiar to plant
personnel.
• A computer can execute a complex
programming task and also multitasking. A
standard PLC is designed to execute a single
program in an orderly fashion. As PLCs are
rapidly changing,
modern PLCs
have
multitasking capabilities.
Why PLCs are so popular?
• Programmable logic controller have made it possible to precisely
control large process machines and driven equipment with less
physical wiring and wiring time than it requires with standard
electro-mechanical relays, pneumatic system, timers, drum switches,
and so on.
• The programmability allows for fast and easy changes in the relay
ladder logic to meet the changing needs of the process or driven
equipment without the need for expensive and time consuming
rewiring process.
• Modem PLCs are "electrician friendly", PLC can be programmed and
used by plant engineers and maintenance electricians without much
electronic and computer programming background. They can
programmed by using the existing ladder diagrams.
Advantage of PLC
No
Advantage
1 Flexibility
Description


2 Implementing Changes and 
Correcting Errors

3 Large Quantity of Contact 
4 Lower Cost

5 Pilot Running (Simulation
Capability)
6 Visual Observation.



7 Speed of Operation

Universal Controller
Can replace various independent/ standalone controller.
Do not have to rewiring relay panel.
Change program using keyboard.
Large number of' Soft Contact' available
Advancement in technology and open architecture of PLC
will reduce the market price.
A program can be simulated or run without actual input
connection.
Can observe the opening and closing of contact switch on
CRT.
Operator message can be programmed for each possible
malfunction.
Depends on scan time -millisecond.
8 Ladder or Boolean Programming Method.
9 Reliability
10 Simplicity of Ordering Control Sys.
Components
11 Documentation
12 . Security
13 Ease of Changes by Programming
 Easy for 'Electrician ,
 In general -very reliable
 One package with Relay, Timers, Control Block, etc.
 Printout of ladder logic can be printed easily
 Software lock on a program (Password)
 Ability to program and reprogram, loading and
down loading
14 Highly versatile (universal applicability)
15 Simple troubleshooting
Simple installation
16 Quick modification of the program (highly
flexible)
17 Capable of task not possible with relays
 Calculation, information exchange, text and graphic
before as indicated by the following:
display, data processing, networking
18 Low space requirement
19 Low power consumption
20 High processing speed
Disadvantages of PLC
N
Disadvantages
o
1 New Technology
2 Fixed program
Application
3 Environment
Consideration
4 Fail-safe operation
Description
 Change from ladder and relay to PLC concept
 Not cost effective for single- function application
 Not adapted for very high temperature, high
humidity level, high vibration, etc.
 Does not start automatically when power failure
( can be programmed into )
 Not "Fail-safe" -Fail-shorted rather than OPEN
5 Fixed-circuit operation  Fixed control system -less costly
What Is Inside A PLC?
Cont.…
• The Central Processing Unit, the CPU, contains an internal
program that tells the PLC how to perform the following
functions:
• Execute the Control Instructions contained in the User's
Programs. This program is stored in "nonvolatile" memory,
meaning that the program will not be lost if power is
removed
• Communicate with other devices, which can include I/O
Devices, Programming Devices, Networks, and even other
PLCs.
• Perform Housekeeping activities such as Communications,
Internal Diagnostics, etc.
How Does A PLC Operate?
• There are four basic steps in the operation of all PLCs; Input Scan, Program
Scan, Output Scan, and Housekeeping. These steps continually take place in
a repeating loop.
1. Input Scan
• Detects the state of all input
devices that are connected to the
PLC
2.Program Scan
• Executes the user created program
logic
3. Output Scan
• Energizes or de-energize all output
devices that are connected to the
PLC.
4.Housekeeping • This step includes communications
with programming terminals,
internal diagnostics, etc...
What Programming Language Is Used To Program A PLC?
• While Ladder Logic is the most commonly used PLC programming language,
it is not the only one. The following lists of some of languages that are used
to program a PLC.
1. Ladder Diagram (LD)
• Traditional ladder logic is graphical programming language. Initially
programmed with simple contacts that simulated the opening and closing
of relays, Ladder Logic programming has been expanded to include such
functions as counters, timers, shift registers, and math operations.
2. Function Block Diagram (FBD)
A graphical language for depicting signal and data flows
through re-usable function blocks. FBD is very useful for
expressing the interconnection of control system algorithms
and logic.
3. Structured Text (ST)
A high level text language that encourages structured
programming. It has a language structure (syntax) that
strongly resembles PASCAL and supports a wide range of
standard functions and operators. For example;
If Speed1 > 100.0 then
Flow_Rate: = 50.0 + Offset_A1;
Else
Flow_Rate: = 100.0; Steam: = ON
End_If;
4. Instruction List (IL)
A low level “assembler like” language that is based on
similar instructions list languages found in a wide
range of today’s PLCs.
LD
MPC
LD
ST
RESET:
ST
R1
RESET
PRESS_1
MAX_PRESS
LD 0
A_X43
5. Sequential Function Chart (SFC)
A method of programming complex control systems at a more highly
structured level. A SFC program is an overview of the control system, in which
the basic building blocks are entire program files. Each program file is created
using one of the other types of programming languages. The SFC approach
coordinates large, complicated programming tasks into smaller, more
manageable tasks.
Input device
1. Switches and Pushbuttons
2. Sensing Devices
• Limit Switches
• Photoelectric Sensors
• Proximity Sensors
3. Condition Sensors
4. Encoders
• Pressure Switches
• Level Switches
• Temperature Switches
• Vacuum Switches
• Float Switches
OUTPUTS
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Valves
Motor Starters
Solenoids
Actuators
Horns and Alarms
Stack lights
Control Relays
Counter/Totalizer
Pumps
Printers
Fans