PLC hardware and architecture
PLCs mainly are built around the central processing unit, a real-time and deterministic processor. It is interfaced with memory units that store programs and data. Most PLCs run on 24 or 48 V DC supply. PLCs are also built modularly by having pluggable cards that can be expanded and customized based on the application scenario. The Input/Output (I/O) cards or modules are usually expandable and can be configured. These cards typically deal with analog and digital signals.
High-speed Pulse-Width Modulation (PWM) sampling circuits are also built in, making the PLCs capable of processing fast signals in real time. The communication modules are, last but not least, key here too. There are communication ports for programming the PLC, obtaining diagnostic information, and interfacing with peer PLCs, networks, and sensors. They help transmit the information upon which the external data logic can be built. Figure 7.1 shows the hardware architecture of a generic...
