Before the proliferation of the IEC 61131-3 standard and the rise of ladder logic in every automation suite, John W. Webb recognized a gap in engineering education. Most textbooks were either too theoretical (heavy on boolean algebra) or too vendor-specific (focusing only on Allen-Bradley or Siemens).
When the first edition was published in 1992, PLCs had only recently displaced relay logic panels in most industries. The 5th edition appeared just as Ethernet was beginning to replace serial communication on the factory floor. Webb and Reis witnessed and documented this transformation. Their book captures an important era in industrial automation history while still providing enduring educational value.
William Bolton's Programmable Logic Controllers (now in its 6th edition) is another strong contender.
: The size of the program and the required scan cycle speed to safely control fast-moving machinery. Before the proliferation of the IEC 61131-3 standard
Maintaining automated systems requires systematic debugging techniques.
Frank Petruzella's Programmable Logic Controllers (now in its 6th edition, McGraw Hill, 2023) is the other major player in the PLC textbook market.
The introduction of the PLC solved these issues by replacing physical wiring with software logic. If a process needs to change, an engineer simply updates the program code rather than rewiring hardware. Core Hardware Architecture of a PLC When the first edition was published in 1992,
: Some used copies of the 5th edition are available for under $20 on sites like AbeBooks. While technically not PDFs, you could legally scan a physical copy for personal use under fair use provisions (for research, teaching, or private study), though distributing scanned copies violates copyright.
Let’s break down what this "updated" edition offers and whether it’s worth the download.
+---------------------------------------+ | Power Supply | +---------------------------------------+ | v +------------------+ +-------------------+ +-------------------+ | Input Modules | --> | Central Processing| --> | Output Modules | | (Sensors/Switch) | | Unit (CPU) | | (Motors/Solenoids)| +------------------+ +-------------------+ +-------------------+ ^ ^ | | v v +--------------------+ +--------------------+ | Programming Device | |Comms Interface/HMI | +--------------------+ +--------------------+ 1. The Central Processing Unit (CPU) Their book captures an important era in industrial
I/O modules act as the senses and muscles of the PLC, bridging the gap between the processor and the physical world.
The CPU is the brain of the PLC. It contains the microprocessor, memory system, and support circuitry. The CPU executes the control program, performs arithmetic and logic operations, and manages communication between other system components. 2. Memory System PLC memory is divided into two primary zones:
Moreover, the installed base of PLCs is enormous, and many factories still run control systems designed decades ago. Understanding "old school" PLC programming (the kind Webb and Reis teach) is essential for maintaining and upgrading legacy equipment.