Glossary · PLC and control programming
Modular PLC
Also known as: Rack-based PLC, Modular controller
German: Modulare SPS
In industrial automation, a modular PLC is a programmable logic controller built from separate modules, such as a CPU, power supply, digital and analog I/O, communication and technology modules, mounted on a rail or backplane and combined as the application requires.
- PLC programming
In one sentence
A modular PLC is assembled from separate CPU, I/O and communication modules, so it can scale to larger machines and plants.
Example
A bottling line uses a modular PLC with a CPU, two communication modules, eight digital I/O modules and a high-speed counter module in one rack.
How it applies
- Engineering: Modular PLCs scale by adding modules and distributed I/O stations. The hardware configuration in the engineering tool must match the physical module order and types; mismatches produce diagnostic errors at startup.
- Maintenance: Many modular systems allow individual I/O modules to be replaced quickly, sometimes during operation. Whether hot swapping is supported depends on the product and must be checked.
- Change management: Module types, firmware versions and the hardware configuration are part of the Configuration baseline of the machine.
- Documentation: Provide a rack or station layout with slot numbers, module order numbers and firmware versions, plus the replacement procedure. Service staff need to know whether a replaced module needs parameters downloaded.
Modular PLC vs. compact PLC
A Compact PLC has built-in I/O and limited expansion. A modular PLC is assembled from modules and scales further. Programming is the same in principle.