Chapter 4 of 12: show all chapters
Chapter 4 of 12Part 2: Inside a control system · 4 min
What is a PLC? The box that decides
In a factory, the deciding is done by a PLC. It is a tough little computer that lives in a metal cabinet near the machine.
PLC stands for programmable logic controller
That is a mouthful, so everyone says PLC. Here is what each word means.
- Programmable: you can give it new rules whenever you like.
- Logic: it follows rules like “if this, then that”.
- Controller: it controls machines.
Why not use a normal computer?
A factory floor is hot, dusty and damp. Big motors fill the air with electrical noise. A normal computer would soon crash. A PLC is built to survive all that and keep going for years.
A PLC also does one job only. It never stops to install updates or open emails. It just keeps checking and deciding.
Where it lives
The PLC sits in a grey metal cabinet with the power switches and wiring. Wires run out of the cabinet to the sensors and motors on the machine.
One PLC can look after one small machine or a whole area of a factory.
Writing the rules for PLCs is most of an automation engineer's job, so they are often called PLC programmers.
Try it
Open the cabinet door and click each part to see what it does.
What is inside?
Seven parts work together in here, with the PLC in the middle. Open the door, then click each part to see what it does.
New words
- PLC
- Programmable logic controller. The tough computer that decides what a machine does.
- Control cabinet
- The metal box that holds the PLC and its wiring.
- Programme
- The full set of rules a PLC follows. Also spelt program.
Quick check
Why do factories use a PLC instead of a normal laptop?