Answer

PLC

A Programmable Logic Controller (PLC) is a rugged industrial digital controller used to monitor inputs, execute a stored control program, and operate outputs for controlling machines and manufacturing processes.

Working of PLC

The basic operation is a continuous scan cycle:

1. Input scan: The PLC reads the status of sensors, switches and other input devices and stores their states in memory.
2. Program execution: The CPU executes the user program, typically written in ladder logic or another IEC 61131-3 language, using the stored input states.
3. Output update: Based on the program result, the PLC updates output devices such as motors, solenoid valves, relays and actuators.
4. Communication/diagnostics: The PLC performs communication and diagnostic tasks as configured.
5. The cycle repeats continuously, allowing the controller to respond to changes in the process.

Block flow: Input devices → Input module → CPU + Program/Memory → Output module → Actuators/process.

Advantages

PLCs are reliable, fast, programmable, easy to modify, suitable for harsh industrial environments, and require less wiring than conventional relay control systems.