A PLC system consists of a CPU, input/output (I/O) modules, and programming software. For motor control, specific I/O modules are used, such as digital outputs for controlling contactors or variable frequency drives (VFDs).
Webb begins with the "hard-wired" past. He explains how old relay control panels worked—using electromagnetic coils and contacts. Then, he demonstrates how the PLC replaces these physical components with memory locations and logic instructions. This historical context is crucial; you cannot debug a PLC program without understanding the ladder logic that mimics relay circuits. A PLC system consists of a CPU, input/output