Summer Internship Report For PLC Programming of Traffic light through Ladder Logic

Industrial Training Project Report
On
PLC PROGRAMMING THROUGH LADDER LOGIC
At
Insulators and Electricals Ltd.
(Training Division of Insulators and Electricals Ltd.)
Submitted to: Submitted by:
Mrs. Shally Goyal Aman Gupta
AP, ECE, ASET B. tech ECE 7th
Sem.
AUMP and ASET, AUMP
Sr. Manager, Personal
Mr. Arun Singhal

Acknowledgement
This report is an outcome of the contributions made by some of the peoples.
Therefore, it is my sole responsibility to acknowledge them. I am greatly thankful
to the sincere efforts made by Mr. Abhaynath Malviya, Senior Industrial
Electronics Engineer, Insulator and Electrical Pvt. Ltd., Bhopal (MP) without whom
this project would be abstract. I also thank the staff of Amity School of Engineering
and Technology who took out their precious time and made various arrangements
for conduction of the classes.
I would also mention the outstanding support given by my parents who paved
the way for me to complete this project report.
AMAN GUPTA
B.tech (7th Sem)
Electronics and Communication Engineering
ASET, AUMP

Preface
An industrial PLCs system is used for the development of the controls of
machinery. This paper describes the PLCs systems in terms of their architecture,
their interface to the process hardware, the functionality and the application
development facilities they provide. Some attention is also paid to the industrial
standards to which they abide their planned evolution as well asthepotentialbenefitsof
theiruse.
Ladder Logic is a graphical programming language, initially programmed with simple
contacts that simulates the opening and closing of relays. Ladder Logic programming
has been expanded to include functions such as Counters, Timers, shift Registers and
math operations.
Ladder logic is a method of drawing electrical logic schematics. It is now a graphical
language very popular for programming Programmable Logic Controllers (PLCs). It
was originally invented to describe logic made from relays. The name is based on the
observation that programs in this language resemble ladders, with two vertical "rails"
and a series of horizontal "rungs" between them.

CONTENTS
Sr. No Headings
1. About the Company
2. Software Used
3. Automation
4. Automation Impacts
5. Introduction to Programmable Logic Circuits (PLC)
6. History of PLCs
7. What is inside a PLC?
8. Input Module
9. Output Module
10. Operation of PLC
11. Programming Languages used for PLC
12. Programming for Start/Stop of Motor by PLC
13. Project
14. Conclusion
15. References

About The Company
IEC stands for Insulators and Electricals Company. It is the policy of IEC to
manufacture & supply Electro Porcelain H.T. Insulators meeting the intended function
and specifications of the customers at a reasonable cost, ensuring their timely delivery.
The company ensures compliance and continual improvement of effectiveness of the
quality management system through involvement of employees at all levels.
IEC has the unique and sophisticated computer controlled Isojet kilns & Photo
copying lathes, six station automatic lathes in addition to the other manufacturing
facilities. This ensures proper firing and most accurate dimensions of insulators.
IEC manufactures high quality Insulators up to 525 kVA that are accepted by buyers
and industries worldwide. We are an ISO-9001-2000 certified company and have also
been approved by LRQA, an U.K. based accrediting company.
IEC has HINDUSTHAN URBAN as the parent company. Established in 1959,
Hindusthan Urban Infratsructure Limited is a leading manufacturer of overhead
conductors & electro – porcelain high tension insulators. We are an ultra – modern,
highly quality – conscious, professionally managed company with sophisticated
European, American & Indian manufacturing & testing machinery. We are reputed
for our impeccable Timely Quality Product Delivery & Performance conforming to
National & International standards. We provide solutions to a diverse set of clients
across India & the Globe with their requirements of Conductors & Insulators.

SOFTWARE USED
All Control Logix and Compact Logix processors use LogixPro 500 software to
program the PLCs. Admittedly, the software is a bit pricey, but in my opinion, it is
worth it.
Getting The LogixPro 500 Software
If you don’t have access to a PLC, it would be well worth the effort to download the
demo version of LogixPro 500. The demo runs for 90 days, and has some
limitations, but you will be gaining experience with the real thing. Currently, the
software is here:
http://www.rockwellautomation.com/rockwellsoftware/design/logixpro500/demo.html
There are 7 sections to download, totaling slightly over 480MB. Yes, it’s a big job to
download and install it, but it is essential.

Automation
Automation or industrial automation is the use of control systems such as computers,
controllers to control industrial machinery and processes, to optimize productivity in
the production of goods and delivery of services. Automation is a step beyond
mechanization. Whereas mechanization provides human operators with machinery to
assist them with the muscular requirements of work, automation greatly decreases the
need for human sensory and mental requirements.
Figure 1

Automation Impacts
It increases productivity and reduce cost. It gives emphasis on flexibility and
convertibility of manufacturing process. Hence gives manufacturers the ability to
easily switch from manufacturing Product A to manufacturing product B without
completely rebuilt the existing system/product lines. Automation is now often applied
primarily to increase quality in the manufacturing process, where automation can
increase quality substantially.
Increased consistency of output.
Replacing humans in tasks done in dangerous environments.

Introduction to Programmable Logic Controller
(PLC)
A PROGRAMMABLE LOGIC CONTROLLER (PLC) is an industrial computer
control system that continuously monitors the state of input devices and make
decisions based upon a custom program to control the state of output devices.
It is designed for multiple inputs and output arrangements, extended temperature
ranges, immunity to electrical noise, and resistance to vibration and impact.
Almost any production process can greatly enhance using this type of control system,
the biggest benefit in using a PLC is the ability to change and replicate the operation
or process while collecting and communicating vital information.
Another advantage of a PLC is that it is modular. i.e. you can mix and match the types
of input and output devices to best suit your application.

History of PLC’s
The first Programmable Logic Controllers were designed and developed by Modicon
as a relay replacer for GM and Landis.
The
primary reason for designing such a device was eliminating the large cost involved in
replacing the complicated relay based machine control systems for major U.S. car
manufacturers.
These controllers
eliminated the need of rewiring and adding additional hardware for every new
configuration of logic. The first PLC, model 084, was invented by Dick Morley in
1969.
The first commercial
successful PLC, the 184, was introduced in 1973 and was designed by Michel
Greenberg. Communications abilities began to appear in approximately 1973. The
first such system was Modicon's Modbus. The PLC could now talk to other PLCs and
they could be far away from the actual machine they were controlling.

What is inside a PLC?
The PLC, being a microprocessor based device, has a similar internal structure to
manyembedded controllers and computers.
They consist of the CPU, Memory an I/O device. These components are integral to
the PLC controller. Additionally, the PLC has a connection for the programming and
Monitoring Unit or to connect PLC’s in other field.
The CPU is the brain of a PLC system. It consists of the microprocessor, memory
integrated circuits, and circuits necessary to store and retrieve information from
memory.
PLC’s or programming terminals. The job of the processor is to monitor status or state
of input devices, scan and solve the logic of a user program, and control on or off state
of output devices.
RAM or Random Access Memory is a volatile memory that would loose its
information if power were removed, hence some processor units are provided with
battery backup. Normally CMOS (Complementary Metal Oxide Semiconductor) type
RAM is used.

ROM is a nonvolatile type of memory. This means it stores it’s data even if no power
is available. This type of memory information can only be read, it is placed there for
the internal use and operation of processor units.
EEPROME or Electrically Erasable Programmable Read Only Memory is usually an
add on memory module that is used to back up the main program in CMOS RAM of
the processor. In many cases, the processor can be programmed to load the
EEPROM’S program to RAM, if RAM is lost or corrupted.
Block Diagram of PLC

INPUT MODULE
Input Module • Input modules interface directly to devices such as switches and
temperature sensors. Input modules convert many different types of electrical signals
such as 120VAC, 24VDC, or 4-20mA, to signals which the controller can understand.
Since all electrical systems are inherently noisy, electrical isolation is provided
between input and processor. The component most often used for this purpose is opt
coupler. Input signal from the field devices are usually 4 to 20 ma or 0-10 V.

OUTPUT MODULE
Output module interface directly to devices such as motor starters and lights Output
modules take digital signals from the PLC and convert them to electrical signals such
as 24VDC and 4 mA that field devices can understand. D to A conversion is carried
out in their modules. Usually Silicon Controlled Rectifier(SCR), trial, or dry contact
relays are used for this purpose. Normally the output signal is 0-10 V or 4-20 ma.

Operation of PLC
PLC operates by continually scanning the program and acting upon the instructions,
one at a time, to switch on or off the various outputs. In order to do this PLC first
scans all, the inputs and stores their states in memory. Then it carries out program
scan and decides which outputs should be high according to the program logic.
Then finally it updates these values to the output table, making the required outputs
go high. At his point PLC checks its own operating system and if everything is ok, it
goes back to scanning inputs all over again.
PLC SCAN CYCLE
Whenever a program is executed in a PLC, before changing any output state, the
processor scans the input table and the entire program, which gives rise to states of the
output devices according to the program logic. These values are then updated to the
output table making the device.
SCAN
TIME
Time taken by plc to execute these three steps (Checking Input status, Executing
Program, Updating Output Status) is denoted by its scan time.

Programming Languages used to Program a PLC
While Ladder Logic is the most commonly used PLC programming language, but it
is not the only one. Following table lists some of the Languages that are used to
program a PLC.
Ladder Diagram (LD).
Functional block Diagram (FBD)
Structured Text (ST)
Instruction List (IL)
Sequential Functional Chart (SFC)
LADDER DIAGRAM
It is a graphical programming language, initially programmed with simple contacts
that simulates the opening and closing of relays. Ladder Logic programming has been
expanded to include functions such as Counters, Timers, shift Registers and math
operations.

A program in ladder logic, also called a ladder diagram, is similar to a schematic for
a set of relay circuits. An argument that aided the initial adoption of ladder logic was
that a wide variety of engineers and technicians would be able to understand and use
it without much additional training, because of the resemblance to familiar hardware
systems.
(This argument has become less relevant given that most ladder logic programmers
have a software background in more conventional programming languages, and in
practice implementations of ladder logic have characteristics — such as sequential
execution and support for control flow features — that make the analogy to hardware
somewhat imprecise.)
Ladder logic is widely used to program PLCs, where sequential control of a process
or manufacturing operation is required. Ladder logic is useful for simple but critical
control systems, or for reworking old hardwired relay circuits. As programmable
logic controllers became more sophisticated it has also been used in very complex
automation systems.
Ladder logic can be thought of as a rule-based language, rather than a procedural
language. A "rung" in the ladder represents a rule. When implemented with relays
and other electromechanical devices, the various rules "execute" simultaneously and
immediately. When implemented in a programmable logic controller, the rules are
typically executed sequentially by software, in a loop.
By executing the loop fast enough, typically many times per second, the effect of
simultaneous and immediate execution is obtained. In this way it is similar to other
rule-based languages, like spreadsheets or SQL. However, proper use of
programmable controllers requires understanding the limitations of the execution
order of rungs.

Example of a simple ladder logic program
The language itself can be seen as a set of connections between logical checkers
(relay contacts) and actuators (coils). If a path can be traced between the left side of
the rung and the output, through asserted (true or "closed") contacts, the rung is true
and the output coil storage bit is asserted (1) or true. If no path can be traced, then
the output is false (0) and the "coil" by analogy to electromechanical relays is
considered "de-energized". The analogy between logical propositions and relay
contact status is due to Claude Shannon.
Ladder logic has "contacts" that "make" or "break" "circuits" to control "coils." Each
coil or contact corresponds to the status of a single bit in the programmable
controller's memory. Unlike electromechanical relays, a ladder program can refer any
number of times to the status of a single bit, equivalent to a relay with an indefinitely
large number of contacts.
So-called "contacts" may refer to inputs to the programmable controller from
physical devices such as pushbuttons and limit switches, or may represent the status
of internal storage bits which may be generated elsewhere in the program.
Each rung of ladder language typically has one coil at the far right. Some
manufacturers may allow more than one output coil on a rung.
--( )-- a regular coil, true when its rung is true
--()-- a "not" coil, false when its rung is true
--[ ]-- A regular contact, true when its coil is true (normally false)
--[]-- A "not" contact, false when its coil is true (normally true)
The "coil" (output of a rung) may represent a physical output which operates some
device connected to the programmable controller, or may represent an internal
storage bit for use elsewhere in the program.

Generally Used Instructions & symbol for PLC Programming
Input Instruction
--[ ]-- This Instruction is Called IXC or Examine If Closed.
If a NO switch is actuated, then only this instruction will be true. If a NC switch is
actuated, then this instruction will not be true and hence output will not be generated.
--[]--
This Instruction is Called IXO or Examine If Open.
If a
NC switch is actuated, then only this instruction will be true. If a NC switch is
actuated, then this instruction will not be true and hence output will not be generated.
Output Instruction
--( )--This Instruction Shows the States of Output.
i.e.; If any instruction either XIO or XIC is true then output will be high. Due to high
output a 24-volt signal is generated from PLC processor.
Rung
Rung is a simple line on which instruction are placed and logics are created
E.g.: ---------------------------------------------

TIMER
A timer is a programmable instruction that lets you turn on or turn off bits after a
preset time.
The two primary types of timers are TON for “timer on delay” and TOF for “timer off
delay”.
Timers in RSLogix 5000 use tag names for identification.
COUNTER
A counter is a programmable instruction that lets you turn on or turn off bits after a
preset count has been reached.
There are different types of counters available in the RSLogix, but the CTU (counter
up) instruction covers everything we will talk about here.
Counters in RSLogix 5000 use tag names for identification.
BIT
An address within the PLC. It can be an input, output or internal coil, among others.

This system allows very complex logic designs to be broken down and evaluated.
Practical Examples
Example-1
------[ ]--------------[ ]----------------O---
Key Switch 1 Key Switch 2 Door Motor
This circuit shows two key switches that security guards might use to activate an
electric motor on a bank vault door. When the normally open contacts of both
switches close, electricity is able to flow to the motor which opens the door. This is
a logical AND.
Example-2
Often we have a little green "start" button to turn on a motor, and we want to
turn it off with a big red "Stop" button.
--+----[ ]--+----[]----( )---
| start | stop run
| |
+----[ ]--+
run
-------[ ]--------------( )---
run motor
Example With PLC

Consider the following circuit and PLC program:
-------[ ]--------------( )---
run motor

When the pushbutton switch is unactuated (unpressed), no power is sent to the X1
input of the PLC. Following the program, which shows a normally-open X1 contact
in series with a Y1 coil, no "power" will be sent to the Y1 coil. Thus, the PLC's Y1
output remains de-energized, and the indicator lamp connected to it remains dark.
If the pushbutton switch is pressed, however, power will be sent to the PLC's X1
input. Any and all X1 contacts appearing in the program will assume t h e actuated
(non-normal) state, as though they were relay contacts actuated by the energizing of
a relay coil named "X1". In this case, energizing the X1 input will cause the normally-
open X1 contact will "close," sending "power" to the Y1 coil. When the Y1coilof the
program "energizes," the real Y1 output will become energized, lighting up the lamp
connected to it:
Lamp Glows when at Input Switch is Actuated
It must be understood that the X1 contact, Y1 coil, connecting wires, and "power"
appearing in the personal computer's display are all virtual. They do not exist as real
electrical components. They exist as commands in a computer program -- a piece of
software only -- that just happens to resemble a real relay schematic diagram.

Equally important to understand is that the personal computer used to display and
edit the PLC's program is not necessary for the PLC's continued operation. Once a
program has been loaded to the PLC from the personal computer, the personal
computer may be unplugged from the PLC, and the PLC will continue to follow the
programmed commands.
It includes the personal computer display in these illustrations for your sake only, in
aiding to understand the relationship between real-life conditions (switch closure and
lamp status) and the program's status ("power" through virtual contacts and virtual
coils).
The true power and versatility of a PLC is revealed when we want to alter the
behavior of a control system. Since the PLC is a programmable device, we can alter
its behavior by changing the commands we give it, without having to reconfigure the
electrical components connected to it. For example, suppose we wanted to make this
switch-and-lamp circuit function in an inverted fashion: push the button to make the
lamp turn off, and release it to make it turn on.
The "hardware" solution would require that a normally-closed pushbutton switch be
substituted for the normally-open switch currently in place. The "software" solution
is much easier: just alter the program so that contact X1 is normally-closed rather
than normally-open.

Programming for Start/Stop of Motor by PLC
Often we have a little green "start" button to turn on a motor, and we want to turn
it off with a big red "Stop" button.
--+----[ ]--+----[]----( )---
| start | stop run
| |
+----[ ]--+
run

The pushbutton switch connected to input X1 serves as the "Start" switch, while the
switch connected to input X2 serves as the "Stop." Another contact in the program,
named Y1, uses the output coil status as a seal-in contact, directly, so that the
motor contactor will continue to be energized after the "Start" pushbutton switch is
released. You can see the normally-closed contact X2 appear in a colored block,
showing that it is in a closed ("electrically conducting") state.
Starting of Motor
If we were to press the "Start" button, input X1 would energize, thus "closing" the
X1 contact in the program, sending "power" to the Y1 "coil," energizing the Y1
output and applying 120-volt AC power to the real motor contactor coil. The
parallel Y1 contact will also "close," thus latching the "circuit" in an energized
state:

Logic for Continuous Running of motor When Start Button is Released
Now, if we release the "Start" pushbutton, the normally-open X1 "contact" will
return to its "open" state, but the motor will continue to run because the Y1 seal-in
"contact" continues to provide "continuity" to "power" coil Y1, thus keeping the Y1
output energized:

To Stop the Motor
To stop the motor, we must momentarily press the "Stop" pushbutton, which will
energize the X2 input and "open" the normally- closed "contact," breaking
continuity to the Y1 "coil:
When the "Stop" pushbutton is released, input X2 will de-energize, returning
"contact" X2 to its normal, "closed" state. The motor, however, will not start again
until the "Start" pushbutton is actuated, because the "seal-in" of Y1 has been lost.

PROJECT: Traffic Light Logic on PLC Using Ladder Logic.
Equipment Required:
Logix Pro Software
Personal Computer
PLC Lab Manual
Theory:
PLC operates by continually scanning the program and acting upon the instructions,
one at a time, to switch on or off the various outputs. In order to do this PLC first
scans all, the inputs and stores their states in memory. Then it carries out program
scan and decides which outputs should be high according to the program logic.
Ladder Logic is a graphical programming language, initially programmed with simple
contacts that simulates the opening and closing of relays. Ladder Logic programming
has been expanded to include functions such as Counters, Timers, shift Registers and
math operations.

Procedure:
1) Make a Ladder Logic of working of Traffic Light.
2) Save the program on Logix Pro Software.
3) Simulate the program and check for errors.
4) Run the program using run option.
5) Program is complete.

Output:
Result: The Ladder logic simulated and Run successfully. The Taffic light worked
perfecly with the PLC program.

Conclusion
Programmable Logic Circuits like an Arduino that is mainly used for industrial
automation. However the main difference between a PLC and an Arduino is their
price, as the PLC usually has 100 times the price of an Αrduino. The PLC has a better
processor power & memory, can handle more current in the I/O ports, the ports are
optocoupled, it is more robust, it is closed architecture, it comes with industrial
certificates, safety features etc.
The Logic made in this project is mainly used for controlling the traffic; and can be
implemented in the industrial sector for controlling the flow of the products and the
production process as it can used for the complex assembly line structure.
At IEC, the main work was to develop solutions based on the same, and hence the
project was selected and the simulation was done.

References
The following is the reference list for any further information:
 http://www.insulatorsindia.com/
 http://www.hindusthanurban.com/
 http://www.amci.com/tutorials/tutorials-what-is-programmable-logic-
controller.asp
 https://en.wikipedia.org/wiki/Programmable_logic_controller
 http://www.allaboutcircuits.com/textbook/digital/chpt-6/programmable-logic-
controllers-plc/
 http://www.plcdev.com/how_plcs_work

Summer Internship Report For PLC Programming of Traffic light through Ladder Logic

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Summer Internship Report For PLC Programming of Traffic light through Ladder Logic