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UNIVERSIDAD AUTONOMA DE TAMAULIPAS

PINTOR CASTILLO SALVADOR

MARCELO MARTINEZ RAUL

FAZ TORRES HILARIO

PEREZ MUÑOZ JOSÉ

JORGE GUSTAVO SILVA DE LA CRUZ

INGENIERO.


INTRODUCTION

THROUGHOUT THE HISTORY OF THE HUMAN BEING, MAN HAS

BEEN CREATING TOOLS AND DEVICES THAT HELP HIM PERFORM

TASKS THAT MAY BE COMPLICATED AND / OR DANGEROUS FOR

HIM; AND THUS, GREAT INVENTIONS OF MACHINES WERE

REACHED THAT HAVE SEVERAL ADVANTAGES AMONG THEM:

MAXIMIZING COSTS, REDUCING RISKS FOR WORKERS,

REDUCING OPERATING TIMES, SERIAL PRODUCTION, ETC.



What is

a PLC?

A PROGRAMMABLE LOGIC CONTROLLER

(PLC) is an industrial computer control

system that continuously monitors the state

of input devices and makes decisions based

upon a custom program to control the state

of output devices.

Almost any production line, machine

function, or process can be greatly enhanced

using this type of control system. However,

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 system is that it

is modular. That is, you can mix and match

the types of Input and Output devices to

best suit your application.

HISTORY OF PLCS

The first Programmable Logic Controllers

were designed and developed by Modicon

as a relay re-placer for GM and Landis.

These controllers eliminated the need

for rewiring and adding additional

hardware for each new configuration of

logic.

The new system drastically increased the

functionality of the controls while

reducing the cabinet space that housed

the 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 Michael Greenberg.

WHAT IS INSIDE A PLC?

The Central Processing Unit, the

CPU, contains an internal program

that tells the PLC how to perform

the following functions:

Execute the Control Instructions

contained in the User's Programs.

This program is stored in

"nonvolatile" memory, meaning

that the program will not be lost

if power is removed

Communicate with other devices,

which can include I/O Devices,

Programming Devices, Networks,

and even other PLCs.

Perform Housekeeping activities

such as Communications, Internal

Diagnostics, etc.

HOW DOES A PLC OPERATE?

There are four basic steps in the

operation of all PLCs; Input Scan,

Program Scan, Output Scan, and

Housekeeping. These steps

continually take place in a repeating

loop.

Four Steps In The PLC Operations

WHAT PROGRAMMING LANGUAGE IS USED TO PROGRAM A PLC?

While Ladder Logic is the most commonly used PLC programming language, it is not

the only one. The following table lists of some of languages that are used to program

a PLC.

Ladder Diagram (LD) Traditional ladder logic is graphical programming language.

Initially programmed with simple contacts that simulated the opening and closing of

relays, Ladder Logic programming has been expanded to include such functions as

counters, timers, shift registers, and math operation.

1.) Input Scan

Detects the state of all input

devices that are connected to

the PLC

2.) Program Scan

Executes the user created

program logic

3.) Output Scan

Energizes or de-energize all

output devices that are

connected to the PLC.

4.) Housekeeping

This step includes

communications with

programming terminals,

internal diagnostics, etc...

Pintor Castillo Salvador Page 03


DICIEMBRE DE 2016

Architecture of PLC

ARCHITECTURE OF PLC

CPU (Central Processing Unit):

PLC system contains of the following parts

Power supply

CPU

Input modules

Output modules

Programming Device

Power Supply :

This module supplies power to the CPU,

input and output modules. It can be built

into the PLC or be an external unit.

Common voltage levels required by the PLC

(with and without the power supply) are

24Vdc, 110Vac, 220Vac.

This module is considered as the brain of

the PLC system and where

ladder logic is stored and processed.

•The memory contains the data and the

ladder program.

It contains an “Executive” program that tells

the PLC how to:

• Execute the control Instructions

• User’s Program

• Communicate with other devices

• Other PLCs, Programming devices, I/O

devices, etc.

• Perform Housekeeping activities

• Diagnostics, etc

This program is stored in “nonvolatile”

memory

• Meaning that the program will not be lost

if power is removed.

I/O MODULES:

Ø The I/O interface section of a PLC

connects it to external field devices.

Ø The main purpose of the I/O

interface is to condition the various

signals received from or sent to the

external input and output devices

Ø Inputs to, and outputs from, a PLC

are necessary to monitor and control a

process. Both inputs and outputs can

be categorized into two basic types:

logical or continuous.

Perez Muñoz Jose Page 04


PLC PROGRAMMING BASICS

The User Program

CPU of the PLC executes two different

programs:

1. The Operating System

2. The User Program

The Operating System

The operating system organizes all the

functions, operations and sequences of the

CPU that are not associated with a control

task. The OS tasks include

Handling a hot restart and warm restart

Updating and outputting the process

image tables of input and outputs

Executing the user program

Detecting and calling the interrupts

Managing the memory areas

Establishing communication with

programmable devices

It is a combination of various functions

which are required to process an

automated task. This must be created by

the users and need to be downloaded to

the CPU of the PLC. Some of the tasks of

the user program include:

Initiating all the conditions for starting the

specified task

Reading and evaluating all binary and

analog input signals

Specifying output signals to all binary and

analog output signals

Executing interrupts and handling errors

1.Textual language

Instructions List (IL)

Structured Text (ST)

2. Graphical language

Ladder Diagrams (LD)

Function Block Diagram (FBD)

Sequential Function Chart (SFC)

PLC Programming Devices

Various types of programming devices are

used to enter, modify and troubleshoot a

PLC program. These programming terminal

devices include handheld and PC based

devices. In the handheld programming

device method, a proprietary device is

connected to PLC through a connecting

cable. This device consists of a set of keys

that allows to enter, edit and dump the

code into the PLC. These handheld devices

consist of small display to make the

instruction that has been programmed

visible. These are compact and easy to use

devices, but these handheld devices have

limited capabilities.

Most popularly a Personal Computer (PC) is used for programming the PLC in conjunction with the software given by the

manufacturer. By using this PC we can run the program in either online or offline mode, and can also edit, monitor,

diagnose and troubleshoot the program of the PLC. The way of transferring the program to the PLC is shown in the

above figure wherein the PC consists of program code corresponding to control application which is transferred to the

PLC CPU via programming cable.

Marcelo Martinez Raul Page 05


LADDER LOGIC PLC PROGRAMMING

Step-By-Step Procedure for Programming

Among several programming languages

ladder logic diagram is the most basic and

simplest form of programming the PLC.

Before going to program the PLC with this

language, one should know some basic

information about it. The below figure

shows the hardwired-ladder diagram

wherein the same lamp load is controlled

by two push button switches, In case if any

one of the switches gets closed, the lamp

glows. Here two horizontal lines are called

rungs which are connected between two

vertical lines called rails. Each rung

establishes the electrical continuity

between positive (L) and negative rails (N)

so that the current flows from the input to

output devices. Some of the symbols used

in ladder logic programming are shown in

the figure.

PLC Using Ladder Logic

The procedure for programming a PLC for a

certain application depends on the type of

standard manufacturer software tool and

the type of control application. But in order

to give a basic guidance to the students,

this atrticle provides a simple approach of

designing control application in PLC

programming software, as given below But

this way of programming doesn’t exactly fit

into all the types of programming tools and

control applications.

The primary step to program the PLC is to

get the idea for which you are going to

develop an application-based program. If

you are driving a line follower robot by the

use of DC motor when the push button is

pressed. This status must be displayed by

the LED light when the motor gets turn on.

The motor is also attached with a sensor

(Here it is considered as another switch)

that detects obstacles, so when this turned

on, the motor should be turned off. And

correspondingly, if the motor switched off,

the buzzer should be turned on.

Faz Torres Hilario Page 06


UNIT

2






GENERAL SPECIFICATIONS

(1) Use this Conductor

Category information for

planning conductor

routing. Refer to

Indistrial Autimation

Wiring and Grounding

Guidelines, publication

1770-4.1

6

Specifications for imputs

Page 11

HILARIO FAZ TORRES

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