具体描述
The programmable logic controller (PLC) is now the control computer of choice in virtually all new industrial control design projects. It has replaced relay logic in almost every control system in current use by being retrofitted into older automation equipment. This complete takeover of the controls market is based on the PLC's ease of programming, reliability, and ability to provide real-time operating data. The computing power of PLCs has steadily increased to the point where the top-of-the-line controllers now have as much, or more, computing power than the standard desktop PC. Programmable controllers can be used to control a variety of industrial machines and processes. These include control applications for automation machinery, process control systems, and HVAC control and monitoring in large buildings. Because PLC systems are now so widely used in industry, everyone from electrical engineers to maintenance technicians needs to have a basic understanding of PLC interfacing and programming. Due to many years of corporate downsizing, most manufacturing engineering groups and maintenance groups are now staffed at minimum levels. This means that engineering and maintenance employees must now cover a much broader range of technology in their organizations. The days of being a mechanical or computer specialist are gone, and employees working in these manufacturing disciplines are expected to be able to handle any problem that arises. Because of this broadening of responsibility, it is now almost mandatory that all engineering and maintenance employees have some background in PLC systems and control systems in general. ORGANIZATION This book presents a comprehensive study of the use of PLC systems in the design of automation equipment. The book begins with a chapter on binary mathematics because understanding binary math is essential to understanding memory addressing, math functions, and I/O address allocations used in PLC systems. Chapters 2 and 3 cover the typical input and output devices and 4odules used in control systems. Examples are provided that demonstrate how sensing devices are interfaced to the PLC control system. Chapters 4 and 5 cover the basic concepts of ladder logic, state diagrams, and flow charts, and how these elements are used to develop ladder programs to control a machine or process. Also covered in detail are the PLC's internal memory layout and I/O scan process. Chapter 6 covers the equipment design process from a project management point of view. This design process has evolved to a team-based design approach that is now used by most companies. Chapter 7 covers the software used in programming the PLC. This includes addressing formats, ladder instruction formats, and their proper uses. Also included are directions for setting up a project from scratch and defining the system's I/O configuration. A sample real-world design problem is presented and a control program is generated to solve the design problem. Chapter 8 covers the basic mechanical building blocks of machine control. The control and interface of air cylinders and air valves are explained along with both rotary and linear indexer devices. Chapters 9 through 11 cover timer and counter instructions with example programs for a variety of real-world control problems. Math instructions, compare instructions, and data handling instructions are also covered in this section. Chapter 12 is devoted to understanding the design problems encountered in controlling manually activated machines. A sample program for a machine of this type is developed and written. Chapter 13 deals with the design problems encountered in controlling continuously running machines. A sample program for a machine of this type is developed and written. Assembly line data tracking and word shift registers are also included in this chapter. Chapters 14 and 15 cover ways to manipulate and track assembly line data. The use of sequencer-driven programs is also covered in detail. Chapter 16 introduces the design of diagnostic programs for monitoring the performance of automation systems. Chapter 17 covers HMI displays and their layout, programming, and interface to the control PLC. CHANGES TO THE SECOND EDITION In response to student requests, a chapter was added to cover the different input devices and sensor devices commonly used in most control system designs today. Because input devices and sensor devices account for more than 75% of the I/O used in most control designs, it was felt that a chapter covering the interfacing and proper use of these devices was required. Each chapter now begins with a list of learning objectives. These objectives will help the student determine if he or she has mastered the concepts presented in each chapter. Hands-on lab projects have been included at the end of each chapter beginning with Chapter 7. The lab projects are designed to reinforce the material introduced in each chapter. Working through the lab project allows the student to experiment and become comfortable with the new information and concepts presented in each chapter. Chapter 13 has a new section that explains how to set up the proper timing sequences for continuously running machines. A sample program was added to demonstrate the basic concepts of cycle timers and methods for stopping the auto cycle only at the end of each assembly operation. Chapter 15, which covers sequences programming, now contains a sample program for demonstrating how to set up and load an SQO/SQC sequences pair function. The book now comes with a student CD that contains copies of all the sample programs covered in the book. As the student is working through the chapter material he or she can download the sample program and examine how it functions on the lab kit. The sample program can then be modified to gain a greater understanding of the concepts covered in the chapter. An Instructor's Manual containing PowerPoint slides of figures, completed lab projects, and all the sample programs found in the book is available online. STUDENT INFORMATION The reader needs to have a basic understanding of electrical systems and machine concepts. Each chapter starts with a list of learning objectives that will be covered in the chapter. Most chapters end with a series of review questions that will test the reader's level of understanding. These review questions should help readers evaluate their level of comprehension of the material presented in the chapter. In addition, beginning with Chapter 7, all chapters end with lab projects that will provide the student with practical hands-on experience on the material covered in the chapter.
