Glossary · PLC and control programming
Compact PLC
Also known as: Fixed PLC, Micro PLC
German: Kompakt-SPS
In industrial automation, a compact PLC is a programmable logic controller that combines the CPU, power supply and a fixed set of inputs and outputs in one housing, often with limited room for expansion modules.
- PLC programming
In one sentence
A compact PLC combines CPU, power supply and a fixed set of I/O in one housing and suits small machines with few signals.
Example
A small conveyor with two motors, four sensors and a stack light is controlled by a compact PLC with 14 digital inputs and 10 digital outputs on board.
How it applies
- Engineering: Compact PLCs are chosen for small machines and standalone functions where the number of signals is known and stable. Designers check early whether the onboard I/O, memory and communication ports are enough, because the expansion options are limited.
- Operation: The fixed design makes spare-part handling simple: one device replaces the controller, power supply and I/O at once.
- Maintenance: When a compact PLC fails, the program and configuration must be restored on the replacement unit. A memory card or a documented backup procedure shortens downtime.
- Documentation: The operating and maintenance manuals should name the exact controller type, firmware version and the location of the program backup, and show the terminal assignment of the onboard I/O.
Compact PLC vs. modular PLC
A compact PLC has a fixed housing with built-in I/O. A Modular PLC is assembled from a CPU and separate I/O, communication and function modules on a rail or backplane, so it scales to larger machines and plants. Both run the same kind of cyclic control program; the difference is hardware architecture and scalability, not programming concept.