Page 20 - Programmable Logic Controllers, Fifth Edition Mobile 2

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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.

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