Glossary Updates12 new terms added to the glossaries · October 2, 2026, 22:44 CEST
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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.

By knowledge.aitechdoc.world · Published September 26, 2026 · Last reviewed

Source: AI TechDoc Knowledge editorial definition, based on common PLC hardware practice and IEC 61131-1

Definitions follow the cited standards and specifications. Where a source is a copyrighted publication, such as an ISO, IEC or EN standard, the definition is a close paraphrase, not a verbatim quotation, so as not to infringe copyright. We recommend reading the original publication. The sections “How it applies” are editorial commentary by AI TechDoc Knowledge and are not part of any standard.

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