Page 20 - Programmable Logic Controllers, Fifth Edition - Mobile version
P. 20

1





                                   Programmable Logic


                                   Controllers (PLCs)


                                   An Overview



































                                                                         Image Courtesy of Rockwell Automation, Inc.
                   Chapter Objectives                                    This chapter gives a brief history of the evolution

                                                                         of the programmable logic controller, or PLC.
                   After completing this chapter, you will be able to:   The reasons for changing from relay control sys-
                      •  Define what a programmable logic controller (PLC) is   tems to PLCs are discussed. You will learn the
                       and list its advantages over relay systems        basic parts of a PLC, how a PLC is used to con-
                      •  Identify the main parts of a PLC and describe their   trol a process, and the different kinds of PLCs
                       functions                                         and their applications. The ladder logic language,
                      •  Outline the basic sequence of operation for a PLC  which was developed to simplify the task of pro-
                      •  Identify the general classifications of PLCs    gramming PLCs, is introduced.















                                                                                                                          1







          pet73842_ch01_001-016.indd   1                                                                                03/11/15   7:08 PM
   15   16   17   18   19   20   21   22   23   24   25