_Ebook__Prentice_Hall_-_Plc_Programming_Methods_And_Applications.pdf

Programmable Logic Controllers:

Programming Methods

and Applications

John R. Hackworth

and

Frederick D. Hackworth, Jr.

Table of Contents

Chapter 1 - Ladder Diagram Fundamentals

Chapter 2 - The Programmable Logic Controller

Chapter 3 - Fundamental PLC Programming

Chapter 4 - Advanced Programming Techniques

Chapter 5 - Mnemonic Programming Code

Chapter 6 - Wiring Techniques

Chapter 7 - Analog I/O

Chapter 8 - Discrete Position Sensors

Chapter 9 - Encoders, Transducers, and Advanced Sensors

Chapter 10 - Closed Loop and PID Control

Chapter 11 - Motor Controls

Chapter 12 - System Integrity and Safety

Preface

Most textbooks related to programmable controllers start with the basics of

ladder logic, Boolean algebra, contacts, coils and all the other aspects of learning to

program PLCs. However, once they get more deeply into the subject, they generally

narrow the field of view to one particular manufacturer's unit (usually one of the more

popular brands and models), and concentrate on programming that device with it's

capabilities and peculiarities. This is worthwhile if the desire is to learn to program that

unit. However, after finishing the PLC course, the student will most likely be employed

in a position designing, programming, and maintaining systems using PLCs of another

brand or model, or even more likely, many machines with many different brands and

models of PLC. It seems to the authors that it would be more advantageous to

approach the study of PLCs using a general language that provides a thorough

knowledge of programming concepts that can be adapted to all controllers. This

language would be based on a collection of different manufacturer types with generally

the same programming technique and capability. Although it would be impossible to

teach one programming language and technique that would be applicable to each and

every programmable controller on the market, the student can be given a thorough

insight into programming methods with this general approach which will allow him or her

to easily adapt to any PLC encountered.

Therefore, the goal of this text is to help the student develop a good general

working knowledge of programmable controllers with concentration on relay ladder logic

techniques and how the PLC is connected to external components in an operating

control system. In the course of this work, the student will be presented with real world

programming problems that can be solved on any available programmable controller or

PLC simulator. Later chapters in this text relate to more advanced subjects that are

more suitable for an advanced course in machine controls. The authors desire that

this text not only be used to learn programmable logic controllers, but also that this text

will become part of the student’s personal technical reference library.

Readers of this text should have a thorough understanding of fundamental ac

and dc circuits, electronic devices (including thyristors), a knowledge of basic logic

gates, flip flops, and Boolean algebra, and college algebra and trigonometry. Although

a knowledge of calculus will enhance the understanding of PID controls, it is not

required in order to learn how to properly tune a PID.

Chapter 1 - Ladder Diagram Fundamentals

1-1. Objectives

Upon completion of this chapter, you will be able to

” identify the parts of an electrical machine control diagram including rungs,

branches, rails, contacts, and loads.

” correctly design and draw a simple electrical machine control diagram.

” recognize the difference between an electronic diagram and an electrical machine

diagram.

” recognize the diagramming symbols for common components such as switches,

control transformers, relays, fuses, and time delay relays.

” understand the more common machine control terminology.

1-2. Introduction

Machine control design is a unique area of engineering that requires the knowledge

of certain specific and unique diagramming techniques called ladder diagramming.

Although there are similarities between control diagrams and electronic diagrams, many

of the component symbols and layout formats are different. This chapter provides a study

of the fundamentals of developing, drawing and understanding ladder diagrams. We will

begin with a description of some of the fundamental components used in ladder diagrams.

The basic symbols will then be used in a study of boolean logic as applied to relay

diagrams. More complicated circuits will then be discussed.

1-3. Basic Components and Their Symbols

We shall begin with a study of the fundamental components used in electrical

machine controls and their ladder diagram symbols. It is important to understand that the

material covered in this chapter is by no means a comprehensive coverage of all types of

machine control components. Instead, we will discuss only the most commonly used ones.

Some of the more exotic components will be covered in later chapters.

Control Transformers

For safety reasons, machine controls are low voltage components. Because the

switches, lights and other components must be touched by operators and maintenance

personnel, it is contrary to electrical code in the United States to apply a voltage higher than

1-1

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