Roadmap › Industrial Automation — PLC, SCADA, Modbus and OPC UA › Module: Field Devices and Signals
Lessons in this course (10)
2. PLC hardware and how a PLC differs from a PC
Basic★ Must knowLesson 2 of 10
A PLC (Programmable Logic Controller) is a rugged industrial computer: CPU, power supply, digital/analog I/O modules, communication modules, often in a rack or as a compact unit.
| PLC | PC | |
|---|---|---|
| Environment | Heat, vibration, electrical noise, 24/7 for decades | Office conditions |
| Timing | Deterministic scan cycle (real-time) | Non-deterministic OS scheduling |
| I/O | Built for direct sensor/actuator wiring | Needs extra hardware |
| Programming | IEC 61131-3 languages | Any language |
| Reliability | Very high, hot-swap modules, redundancy options | Lower |
Related controllers: DCS (Distributed Control System — plant-wide continuous processes such as refineries, tightly integrated with its own HMI, e.g. Emerson DeltaV, ABB 800xA, Honeywell Experion); PAC (programmable automation controller — PLC + PC features); RTU (remote terminal unit for remote sites like pipelines); safety PLC (SIL-rated, e.g. Siemens F-CPU, GuardLogix); soft/virtual PLC running on industrial PCs.