An introduction programmable logic controllers (PLCs). It avoids detailed programming instructions and presents the subject in a way that is not device-specific. The book aims to enable the reader to: identify the main design characteristics and internal architecture of PLCs; describe and identify the characteristics of commonly-used input and output devices; explain the processing of inputs and outputs by PLCs; describe communication links involved with control systems; develop ladder programs for the logic functions AND, OR, NOR, NAND, NOT and XOR; develop ladder programs involving internal relays, timers, counters, shift registers, sequencers and data handling; and identify methods used for testing and debugging. The second edition includes expanded sections on internal architecture, input-output devices, networks, and programming languages with microprocessor systems.