2. CONTENTS
INTRODUCTION
PLC VERSUS RELAY LOGIC
ADVANTAGES AND DISADVANTAGES
UNIT OF PLC
CPU PROCESSOR,MEMORY ANDPOWER SUPPLY.
INPUT/OUTPUT MODULES
INPUT /OUTPUT DEVICES AND SENSORS
PLC PROGRAMMING
PlC USED IN DIFFERENT PROCESS PLANT OF SPF
PLC INSTALLATION,TROUBLE SHOOTING MAINTENANCE
SELECTING A PLC
MANUFACTURES
OTHER APPLICATIONS(ROBOTS,SCADA System)
3. INTRODUCTION
A plc is a microprocessor –based specialized computer that carries out control function
of many types and levels of complexity .
PLC purpose is to monitor crucial process parameter and adjust process operations
accordingly.
PLC takes the place of much of the external wiring required for control of a process
The PLC can be operated on the input side by on-off devices such as digital and also
analog input devices
PLC will operate any system that has output devices that go on and off and also operate
any system with variable output.
4. PLC VS CONTROLLER
Good Things about PLC’s
Uses Ladder programming language through high end software
They are highly reliable, fast and flexible.
They can handle severe conditions such as dust, humidity etc.
They can communicate with other controllers.
They are easy to program and troubleshoot.
They include display units.
It is for industrial automation.
Trouble shooting, signal interfacing
Input/output expandables usually programmed through external PC program
Good Things about Micro Controller
Design our own signal interfacing
Machine language use for programming.
Input/output cannot be expandables.
5. PLC VERSUS RELAY LOGIC
Before PLC introduced,Relay -type control panel used in
process control.It is large and contains lots of wiring
,interconnections and relays,which can have the
maintenance problems.
The first PLC system evolved in the late 1960s and early
1970s and these first PLCS were installed in automotive
plants.
IN 1972 ,the introduction of microprocessor chip increased
computer power for all kinds of automation system s and
lowered the computer cost.
IN 1980,large electronics and computer companies found
that PLC had become their greatest volume product.
8. PLC AS A COMPUTER
A Plc is a computer ,but a different type from the desk
or lap computer.Micro computers are data processing
computers while PLC is a process control computer.
Data processing
Computer
system
Video
display
terminal
Printer
plotter
Keyboard
Light Pen
Mouse
10. ADVANTAGES
Flexibility
Implementing changes and correcting Errors
Lower cost
Visual observation
Speed of operation
Reliability and Maintainability
Security
Ease of changes by reprogramming
11. UNITS OF PLC
There are four major units of a plc system
1.Central processing unit(CPU)
a.Microprocessor
b.Memory
c.Power supply
2.Programmer /Monitor
3.I/O Modules
4.Racks and chassis
12. Central Processing unit
The central processing unit (CPU) is the part of a
programmable controller that retrieves,decodes,
stores, and processes information.
It also executes the control program stored in the PLC’s
memory.
The CPU is the “brains” of a programmable controller.
It functions much the same way the CPU of a regular
computer does, except that it uses special instructions
and coding to perform its functions.
13. MEMORY
There are two types of memory in plc
Read only memory (Rom)
Random access memory(Ram)
ROM
The programmable read only memory (PROM) chip is similar to
the ROM except it may be programmed once.
The Erasable programmable read only memory (EPROM) is a
PROM that can be erased.The EPROM is erased by ultra violet
light.
The electrically erasable programmable read only memory
(EEPROM) is similar to the EPROM.Instead of UV light
,Electrical signal is applied to erase the program.
14. RAM
The EEPROM is used in place of RAM.
EEPROM is the memory for storing ,backing up,or
transferring PLC programs.
The nonvolatile random access memory (NOVRAM) is
a combination of EEPROM and RAM.
When the power is about to go off,the contents of the
RAM memory are quickly stored in the EEPROM.
The stored data can then be read in to the RAM
memory when the power is again restored.
16. PROCESSOR
The processor is the part of the CPU that codes, decodes,
and computes data.The data is in digital pulse form ,is sent
and received.
Microprocessors power are determine by two factors
Bit size and clock speed.
There are 4,8,16,32 and 64-bit microprocessor ,which
manipulate data 4,8,16,32 or 64 bits at a time.
Clock speed determines how quickly a microprocessor
executes instruction
Clock speeds range from a low of 1 megahertz(MHZ) to
over 1 giga hertz (GHZ)
18. POWER SUPPLIES
The power available in most plants is 220 volts
alternating current (AC) at 60 HZ.Most PLC operate
on +5 and -5 volts DC.
The circuitry is needed to convert 220 v AC input to
the required 5 volt DC values.
LINE
CONDITIO
NER
Rectifi
er
Filter Regula
tor
Back
up
battery
19. Input Modules
The input module perform four task electronically
1.It senses the presence or absence of an input signal at
each of its input terminal
2.It converts the input signal for high to a DC level
usable by the modules electronic circuit.
3.The input module carries out electronic isolation by
electronically isolating the input module output from
its input.
4.Its electronic circuit must produce an output via
output logic to be sensed by the PLC CPU.
26. OUTPUT MODULES
A DC signal from the CPU is converted through each
module terminal to a usable output voltage ,either AC
or DC.
A signal from the CPU is received by the output
module if the cpu signal code matches the assigned of
the module.the module section will turned on.
Isolation is necessary to the output of the cpu so that
any erratic voltage surge from the output device does
not get back in to the CPU and cause damage.
36. PLC PROGRAMMING
There are five types of PLC programming which are
normally used.
1.Ladder logic Diagram
2.Function Block Diagram(FBD)
3.Boolean Language
4.Structured Text(ST)
5.Instruction List(IL)
37. LADDER LOGIC DIAGRAM
The ladder diagram has two active functional lines.The
format of control ladder diagrams is
1.All coils,pilot lights and outputs are on the right
2.An input line can feed more than one output.so connect in
parallel.
3.Switches and contacts are inserted on the lift side.
4.Switches and contacts may be multiple contacts in
series,parallel
5.Lines are numbered consectively downward on the left.
6.Every connection node is given a unique identification
number
7.Output can be identified by function on the right
73. PLC Installation
These are the factors which should be considered to ensure continuous ,reliable operation of PLC system
after installation.
1.Enclosure:
The PLC can be installed in the open ,NEMA(National electrical manufacturing association )type metal
enclosure.
2.Temperature:
The PLC has upper and lower temperature operationg limit normally 0 c to 60 c.
3.Moisture,Dust and Corrosive Atmosphere:
PLC may be required to operate in an area of high humidity,less moisture and dust.
4.Vibration:
Vibration also cause CPU failure and reduce the life of Plc equipment.
5.Proper Electriacal grounding:
Proper electrical grounding of the wiring of the equipment and cabinets is essential for proper
equipment operation.
6.Suppressor:
Suppression is the technique to absorbs the inductive –caused electrical disturbance.These electrical
disturbances in the air can be reduced by the use of shielded interconnecting cables.
7.Master control relay:
Master relay control system is used to safety shut down of the PLCoperation.When on the safety
shutdown allows the PLC to operate and when deenergi
74. Testing
Testing can be done in any one of three modes
1.PLC can be tested as without attaching any wiring to
the I/o module.
2.It may be tested with a simulator
3.It may be tested after it is hooked up to the system to
operate.
75. Troubleshooting Of PLC
Enter 1
use program loader
and retest processor
Turn to run position
Did fault
Clear
Resume Normal
operation
Enter 2
Disconnect
I/O Flat
cable at
processor
Probable
cause
:defective
I/O Interface
Replace
Processor
Initialize and
load
program
Replace I/O
flat cable
did
fault
clear
Resume
Normal
Operation
Resume
Normal
operation
Reconnect
I/O flat cable
to Processor
Disconnect
all racks
from I/O
Flat cable
Did
Fault
Occur
connect one
I/O Rack at a
time untill
fault occur
A
76. PLC MAINTENANCE
1.Periodically check the tightness of I/O module
terminal screws
2.Moisture and corrosive atmosphere can cause poor
electrical connection.Check periodically for corrosion
of connecting terminal.
3.Make sure that components are free of dust.Proper
cooling is required for Plc.
4.Replace the PlC back up batteries once in a year.
77. Selecting a Plc
These are the factors which have to considered in
selecting a PLC.
1.Cost
2.Service abilitiy/Support
3.Flexibility/Expandability
4.Training /Documentation.
78. MANUFACTURES
ABB Automation
Control Microsystems
CTC Parker Automation
Intelligent Instruments
Mitsubishi Electric Automation
Moeller Corp.
Omega Engineering
Schneider Electric
Siemens Energy & Automation
Toshiba International Corp.
