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What Is a PLC? Basic Architecture

The basic structure of a Programmable Logic Controller (PLC): CPU, I/O modules, power supply and communication.

5 min readUpdated: 2026-07-05

A PLC (Programmable Logic Controller) is a rugged industrial computer that controls processes in real time. It reads data from sensors, decides according to program logic, and drives outputs (motors, valves, relays).

Core components

CPU
Program execution + memory
Input (I)
Sensor/button signals
Output (O)
Driving motors/valves/relays
Communication
PROFINET, Modbus, EtherCAT…
Modern PLCs can be compact (integrated I/O) or modular (rack-based); modular designs give flexibility in large plants.

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