What is a PLC?
A PLC (Programmable Logic Controller) is an industrial electronic device designed to automatically control processes and machinery. Invented in the 1960s as a replacement for complex electromechanical relay systems, it is today the central component of any industrial automation system.
Unlike a conventional computer, a PLC is designed to operate in hostile industrial environments: it withstands extreme temperatures, vibrations, dust and electrical noise. It operates in real time with high reliability — essential in a production environment where a failure can mean costly downtime.
How does a PLC work?
The PLC works in a continuous cycle called the scan cycle:
- Input reading: the PLC reads the state of all sensors and input signals (buttons, detectors, encoders...)
- Program execution: processes the control logic programmed by the engineer
- Output writing: activates or deactivates the corresponding outputs (motors, valves, lights...)
This cycle repeats thousands of times per second, enabling near-instantaneous control of the process.
Main PLC manufacturers
- Siemens (Germany): with the S7 family (S7-1200, S7-1500) and TIA Portal programming environment — the European standard.
- Beckhoff (Germany): PC-based automation with TwinCAT, ideal for high-precision motion control.
- Rockwell Automation / Allen-Bradley (USA): industry reference in North America and energy sector. Studio 5000 with ControlLogix.
- Schneider Electric (France): Modicon family, widely used in infrastructure and continuous processes.
- Codesys: open runtime platform used by dozens of hardware manufacturers.
PLC types by size
- Micro/Nano PLC: for small machines with few I/O. E.g. Siemens S7-1200.
- Compact PLC: all integrated in one module. For medium applications.
- Modular PLC: expandable architecture with I/O modules. E.g. Siemens S7-1500, ControlLogix.
- Process PLC (DCS): for complex continuous processes like chemical or water treatment plants.
PLC applications in industry
- Power plants and energy installations
- Palletising and automated logistics
- Industrial robot control
- Feeding and dosing systems in food and pharma
- Furnace, press and moulding machine control
- Building management systems (BMS)
- Water treatment plants
How to choose the right PLC?
- Number of I/O: how many digital and analogue inputs/outputs you need
- Cycle speed: if the application requires motion control or very fast response times
- Communications: which protocols you need (Profinet, EtherNet/IP, Modbus, OPC-UA...)
- Client standard: many companies have an approved manufacturer
- Total cost: hardware + software + training + maintenance
At Bluemation we program PLCs from all major manufacturers: Siemens, Beckhoff, Rockwell, Schneider and Codesys. Contact us if you need advice on the best platform for your project.