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Programmable Logic Controllers and Ladder Logic

Programmable Logic Controllers and Ladder Logic -...

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PROGRAMMABLE LOGIC CONTROLLERS AND LADDER LOGIC Submitted to Dr. Alfred R. Boysen Department of Humanities South Dakota School of Mines and Technology Technical Communications I By Greg P. Zimmerman April 2008 1
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13361 Gideon’s Trail Keystone, SD 57751 April 10, 2008 Dr. Alfred R. Boysen Department of Humanities South Dakota School of Mines and Technology Rapid City, South Dakota 57701 Dear Dr. Boysen: I am submitting the following report, “Programmable Logic Controllers and Ladder Logic,” for English 279 – Technical Communications I. This report discusses: 1) PLC and controls history, 2) PLC components, 3) ladder logic, and 4) ladder logic programming. I would like to take this time to thank you Dr. Boysen, for making this class the first English class I have enjoyed. Your teaching techniques are one of the main reasons in my continued interest in English and the liberal arts. Your flexibility with me and my own techniques has helped me to learn more about myself as well. This is the first paper that I have enjoyed writing in quite a long time, and this is because I was allowed to write it about what I wanted to write about. When I enter the workforce, I will remember what you have taught me so that I may be better able to communicate my ideas to my coworkers, investors, or whoever else it may be. In this report I hope to further the reader’s understanding of logic controllers and ladder logic. Sincerely, Greg P. Zimmerman Electrical Engineering Undergraduate 2
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TABLE OF CONTENTS List of Figures .................................................................................................... ........................... 4 Abstract ..................................................................................................................... .................... 5 Introduction ................................................................................................................................... 6 Subject ............................................................................................................ ................... 6 Purpose ....................................................................................................... ....................... 7 Plan of Development ........................................................................................................ .. 8 PLC History ........................................................................................................... ....................... 9 PLC History ......................................................................................................... .............. 9 Hard-Wired Relay Comparison .............................................................................. .......... 10 PLC Components .............................................................................................................. .......... 13 Definition ............................................................................................................... .......... 13 Components ................................................................................................... .................. 13 PLC Operation ................................................................................................ ................. 16 Ladder Logic ............................................................................................................. .................. 19 Definition ............................................................................................................... .......... 19 Comparison to Relay Logic .................................................................. ........................... 20 Ladder Logic Programming ................................................................................................... .... 25 Introduction .................................................................................................................... .. 25 Basic AND & OR Gates ................................................................................................ ... 27 Basic Timers and Counters .............................................................................................. . 28 Building a PLC/Ladder Logic Program ................................................ ........................... 29 Conclusion ................................................................................................................... ................ 33 Summary .................................................................................................................... ...... 33 Closing Summary ............................................................................................................ . 33 3
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LIST OF FIGURES Figure 1: Typical Small Scale Control Panel ..................................................................... 11 Figure 2: Typical PLC Control Panel ................................................................................. 12 Figure 3: PLC Components Diagram ................................................................................ 15 Figure 4: PLC Scan Diagram ............................................................................................. 17 Figure 5: Basic Ladder Logic Program .............................................................................. 19 Figure 6: Electromechanical Relay .................................................................................... 20 Figure 7: Basic Relay Logic Circuit .................................................................................. 21 Figure 8: Relay Logic Circuit with Jog function added ..................................................... 22 Figure 9: Relay Logic Circuit with Jog function and Status Indicators ............................. 22 Figure 10: Complex Ladder Diagram ................................................................................ 23 Figure 11: Simplified Logic Circuit ................................................................................... 25 Figure 12: Simplified AND gate ........................................................................................ 27 Figure 13: Simplified OR gate ........................................................................................... 27 Figure 14: On-Delay Timer (RTO) .................................................................................... 28 Figure 15: Up Counter ....................................................................................................... 29 Figure 16: Ladder Diagram in Relay Logic ....................................................................... 29 Figure 17: Relay Diagram with overload removed ............................................................ 30 Figure 18: Relay Circuit with Addition of Jog Function ................................................... 30 Figure 19: Relay Circuit with Addition of Status Indicators ............................................. 31 Figure 20: Relay Logic Diagram Converted to PLC Ladder Logic ................................... 32 4
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ABSTRACT This report answers basic questions that may be posed by anyone in the Electrical Engineering field, including electrical engineering technicians and electricians. The reader does not need to have any background in controls or ladder logic; only an interest in how PLCs work and a basic understanding of digital logic. The questions that will be
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