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Industrial Training on PLC programmable logic controlle

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    A SUMMER INTERNSHIP PROJECT REPORT

    ON

    PLC PROGRAMMING THROUGH LADDER LOGIC

    SUBMITTED TO:

    AMITY SCHOOL OF ENGINEERING & TECHNOLOGY

    AMITY UNIVERSITY, MADHYA PRADESH, GWALIOR

    SUBMITTED BY:

    AMAN GUPTA

    Bachelor of Technology

    Electronics and Communication Engineering

    Enrolment no: A602051120132012- 16

    UNDER THE SUPERVISION OF

    Mr. ABHAYNATH MALVIYASenior Industrialist Electronics Engineer

    Insulator and Electrical pvt. Ltd.

    Bhopal (MP)

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    CERTIFICATE

    I hereby certify that the work which is being presented in the B.tech. SummerInternship Project Report entitled PLC Programming through Ladder Logic,

    in partial fulfilment of the requirements for the award of the Bachelor of Technology

    in Electronics and Communication Engineeringand submitted to the Department

    of Electronics and Communication Engineering ,Amity School of Engineering and

    Technology is an authentic record of my own work carried out during a period from

    May 2015 to July 2015 under the supervision of Mr. Abhaynath Malviya, Senior

    Industrialist Electronics Engineer, Insulator and Electrical pvt. Ltd., Bhopal (MP)

    The matter presented in this thesis has not been submitted by us for the award of anyother degree elsewhere.

    Date: 27/8/15 Aman Gupta

    A60205112013

    B.tech ECE 7thSem

    ECE ASET AUMP

    Mr. Abhaynath Malviya

    Senior Industrialist Electronics Engineer

    Insulator and Electrical pvt. Ltd. Bhopal (MP)

    Mrs. RINKOO BHATIA

    HEAD OF DEPARTMENT

    Department of Electronics and Communication EngineeringAmity School of Engineering & Technology, AUMP.

    Dr. ANSHUL GANGELE

    HEAD OF INSTITUTEAmity School of Engineering & Technology, AUMP.

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    DECLARATION

    I hereby declare that this summer internship report on PLC Programming Through

    Ladder Logicis my own work and that, to the best of our knowledge and belief, it

    contains no material previously published or written by another person nor material

    which to a substantial extent has been accepted for the award of any other degree or

    diploma of the university or other institute of higher learning, except where due

    acknowledgment has been made in the text.

    Aman Gupta Place: GwaliorA60205112013 Date: 28/8/2015B.tech (7thSem)Electronics and Communication EngineeringASET, AUMP

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    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 tothe sincere efforts made by Mr. Abhaynath Malviya, Senior IndustrialistElectronics Engineer, Insulator and Electrical pvt. Ltd., Bhopal (MP) without whomthis project would be abstract. I am very much thankful to our Honble Vicechancellor Lt.Gen.V. K. SharmaRetd. (AVSM) for allowing me to carry out mysummer internship. I extend my sincere thanks to Prof. (Dr.) Rajesh Singh Tomar,Dean (Academics).

    I would like to thank Mrs Shally GoyalAsst. Prof. ECE ASET and Mrs RinkooBhatiaHOD ECE ASET. I also thank the staff of Amity School of Engineering andTechnology who took out their precious time and made various arrangements forconduction of the classes.

    I would also mention the outstanding support given by my parents who paved theway for me to complete this project report.

    Aman Gupta

    A60205112013B.tech (7th sem.)Electronics and Communication EngineeringASET, AUMP

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    LIST of ABBREVATIONS

    PLC: programmable logic controllerOSR: one shot rising

    KVA: kilo volt ampere

    SCADA: supervisory control and data acquisition

    LL: ladder logic

    DRAM: Dynamic random-access memory

    CPU: central processing unit

    Ladder Diagram

    FBD: Functional block Diagram

    ST: Structured Text

    IL: Instruction List

    SFC: Sequential Functional Chart

    EN: enable

    DN: Disable

    TON: timer on

    TOF: timer off

    I/O: input and output

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    TABLE of CONTENTS

    Cover PageCertification

    Declaration

    Acknowledgement

    List of Abbreviations

    Abstract.. 1

    Introduction.2

    Review of Literature.......3

    About The Company4-7

    Software Used....8-10

    What is inside a PLC?................................................................................11-20

    Operation on PLC.....21-30

    Project...........31-33

    Conclusion.34

    References..35

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    ABSTRACT

    The purpose of this Programmable Logic Controller (PLC) is to command 16

    relays in different sequences programmed by user. This device is applicable for

    controlling and monitoring industrial processes and may be implemented in multiple

    domains, from auto industry and home control applications to industrial instruments

    remote sensors and security devices. Its also ideal for battery powered devices

    because its low power consumption. EEPROM memory make easier the

    implementation of the microcontroller on devices where permanent memory is

    needed to store different parameters (codes for transmitters, motor speed, receiver

    frequencies). The controller can be used in small industry in controlling andmonitoring industrial processes. Depending of the programmed software, the device

    can

    i) command a packing line

    ii) count the products from an industrial process line and display the result on

    any kind of display, and

    iii) communicate with dedicated PLCs using digital level shifters.

    Key words: Programmable Logic Controller, EEPROM.

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    INTRODUCTION

    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 interfaceto the process hardware, the functionality and the application development facilitiesthey provide. Some attention is also paid to the industrial standards to which theyabide their planned evolution as well as the potential benefits of their use.

    Ladder Logic is a graphical programming language, initially programmed withsimple 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 graphicallanguage very popular for programming Programmable Logic Controllers (PLCs). Itwas originally invented to describe logic made from relays. The name is based on theobservation that programs in this language resemble ladders, with two vertical "rails"and a series of horizontal "rungs" between them.

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    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 deliveryThe 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 alsobeen 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 & electroporcelain high tension insulators. We are an ultramodern

    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.

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    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 isworth it.

    Getting The LogixPro 500 Software

    If you dont 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 somelimitations, 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, its a big job to

    download and install it, but it is essential.

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    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 toassist them with the muscular requirements of work, automation greatly decreases the

    need for human sensory and mental requirements.

    Figure 1

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    AUTOMATION IMPACTS

    It increases productivity and reduce cost. It gives emphasis on flexibility andconvertibility 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 dangerousenvironments.

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    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.

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    HISTORY of PLCs

    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.

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    WHAT is INSIDE a PLC?

    The PLC, being a microprocessor based device, has a similar internal structure to

    many embedded 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 PLCs 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.

    PLCsor programming terminals. The job of the processor is to monitor status or state

    of input devices, scan and solvethe 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.

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    ROM is a nonvolatile type of memory. This means it stores itsdata 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 ofthe processor. In many cases, the processor can be programmed to load the

    EEPROMSprogram to RAM, if RAM is lost or corrupted.

    Block Diagram of PLC

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    INPUT MODULE

    Input Module Input modules interface directly to devices such as switches andtemperature 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.

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    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 carriedout 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.

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    OPERATION of PLC

    PLCoperates 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 firstscans 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 theentire 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, ExecutingProgram, Updating Output Status) is denoted by its scan time.

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    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 toprogram 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.

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    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.

    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 programmershave a software background in more conventional programming languages, and in

    practice implementations of ladder logic have characteristicssuch as sequential

    execution and support for control flow featuresthat 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.

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    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, thenthe 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 indefinitelylarge 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.

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    GENERALLY USED INSTRUCTIONS and SYMBOL for PLC

    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 begenerated.

    Output Instruction

    --( )-- This Instruction Shows the States of Output.

    i.e.; If any instruction either XIO or XIC is true then outputwill be high. Due to high

    output a 24-volt signal isgenerated from PLC processor.

    Rung

    Rung is a simple line on which instruction are placed and logics are created

    E.g.: ---------------------------------------------

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    TIMER

    A timer is a programmable instruction that lets you turn on or turn off bits after a

    preset time.

    The twoprimary 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.

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    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 isa 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

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    Consider the following circuit and PLC program:

    -------[ ]--------------( )---run motor

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    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 lampconnected 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 rea

    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.

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    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 alterits 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 ratherthan normally-open.

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    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

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    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:

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    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:

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    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.

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    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.

    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.

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    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.

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    Output:

    Result: The Ladder logic simulated and Run successfully. The Taffic light worked

    perfecly with the PLC program.

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    CONCLUSION

    Programmable Logic Circuits

    like an Arduino that is mainly used for industrialautomation. However the main difference between a PLC and an Arduino is their

    price, as the PLC usually has 100 times the price of an rduino. 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 theproduction 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.

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    REFRENCES

    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

    http://www.insulatorsindia.com/http://www.insulatorsindia.com/http://www.hindusthanurban.com/http://www.hindusthanurban.com/http://www.amci.com/tutorials/tutorials-what-is-programmable-logic-controller.asphttp://www.amci.com/tutorials/tutorials-what-is-programmable-logic-controller.asphttp://www.amci.com/tutorials/tutorials-what-is-programmable-logic-controller.asphttp://www.amci.com/tutorials/tutorials-what-is-programmable-logic-controller.asphttp://www.amci.com/tutorials/tutorials-what-is-programmable-logic-controller.asphttps://en.wikipedia.org/wiki/Programmable_logic_controllerhttps://en.wikipedia.org/wiki/Programmable_logic_controllerhttp://www.allaboutcircuits.com/textbook/digital/chpt-6/programmable-logic-controllers-plc/http://www.allaboutcircuits.com/textbook/digital/chpt-6/programmable-logic-controllers-plc/http://www.allaboutcircuits.com/textbook/digital/chpt-6/programmable-logic-controllers-plc/http://www.allaboutcircuits.com/textbook/digital/chpt-6/programmable-logic-controllers-plc/http://www.allaboutcircuits.com/textbook/digital/chpt-6/programmable-logic-controllers-plc/http://www.plcdev.com/how_plcs_workhttp://www.plcdev.com/how_plcs_workhttp://www.plcdev.com/how_plcs_workhttp://www.allaboutcircuits.com/textbook/digital/chpt-6/programmable-logic-controllers-plc/http://www.allaboutcircuits.com/textbook/digital/chpt-6/programmable-logic-controllers-plc/https://en.wikipedia.org/wiki/Programmable_logic_controllerhttp://www.amci.com/tutorials/tutorials-what-is-programmable-logic-controller.asphttp://www.amci.com/tutorials/tutorials-what-is-programmable-logic-controller.asphttp://www.hindusthanurban.com/http://www.insulatorsindia.com/

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