Preface Technological advances in recent years have resulted in the development of the programmable logic controller (PLC) and a consequential revolution of control engineering. This book, an introduction to PLCs, aims to ease the tasks of practicing engineers coming into contact with PLCs for the first time. It also provides a basic course for students in curricula such as the English technicians' courses for Nationals and Higher Nationals in Engineering, giving full syllabus coverage of the National and Higher National in Engineering units, company training programs, and serving as an introduction for first-year undergraduate courses in engineering. The book addresses the problem of various programmable control manufacturers using different nomenclature and program forms by describing the principles involved and illustrating them with examples from a range of manufacturers. The text includes: · The basic architecture of PLCs and the characteristics of commonly used input and outputs to such systems A discussion of the number systems: denary, binary, octal, hexadecimal, and BCD ·