emphasis on program design. This text stresses an organized approach to developing PLC programs - Given a set of operational specifications, how does one develop the PLC program? This book develops the design process: the tasks involved, breaking the program into manageable pieces, standard code for the various parts, and handling the sequential parts of the problem. Throughout, the book contains example problems demonstrating good design practice and culminates in two full-length case studies. Due to its popularity, ladder logic is employed in the majority of the text. However, the text also comprehensively covers the other four IEC 61131-3 languages: function block diagram, structured text, instruction list, and sequential function chart. These languages are covered for five PLCs: Allen-Bradley ControlLogix, Allen-Bradley PLC-5/SLC-500, Modicon Unity, Siemens S7, and GE. The main topics of this text are: 1. PLC programming languages (with emphasis on IEC 61131-3) 2. Structured approach to sequential problems 3. Good program design practice 4. Troubleshooting techniques 5. PID control 6. Sensors and actuators 7. Factory communication networks 8. Human-machine interface (HMI) Most chapters include student problems. The accompanying CD contains 59 additional problems with solutions for chapters 2, 3, 5, 6, 7, 9, 10, 13. Changes for the Second Edition The second edition primarily updates the Modicon, Siemens, and GE controllers to the current processors, but there are other changes throughout. The major changes are: 1. The Modicon sections focus on the Modicon Unity processors. 2. The Allen-Bradley material has been updated to focus on the ControlLogix processor, though the PLC-5/SLC-500/MicroLogix processors are also covered. Coverage of the ControlLogix add-on instruction (AOI) has been added. 3. The Siemens S7-1200 has been added to the Siemens sections and the material on the S5-compatible timers and counters has been removed. 4. The GE PACSystems processor has been added and the material focuses on this processor with references to the earlier processors as appropriate. 5. The accompanying CD contains the PLC projects for each text example problem and has an additional set of problems with solutions. 6. The examples in sections 9.2, 11.7 and 21.4 now utilize user-defined data types and user-defined function blocks. 7. In Chapter 17, the device-level Ethernet ring topology is introduced, peer-to-peer communications for the S7-300/400 emphasizes the use of Ethernet and the AG_SEND/AG_RECV blocks, and communication heartbeats are covered.

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