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 as the potential benefits of

their use.

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

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 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.

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 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.

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.

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