IEC 61131-1:2003

Overview

IEC 61131-1:2003 - Programmable controllers: Part 1, General information - is the International Electrotechnical Commission (IEC) standard that establishes the vocabulary, scope and principal functional characteristics of programmable logic controllers (PLCs) and their associated peripherals (for example, programming and debugging tools (PADTs), human‑machine interfaces (HMIs), remote I/O stations, field devices). This second edition (2003) supersedes the 1992 edition and provides the foundational definitions and architectural descriptions used across the IEC 61131 series.

Key topics and technical requirements

• Definitions and terminology: standardized terms for PLC components and concepts (e.g., application programme, PADT, remote I/O station (RIOS), ladder diagram).
• Functional architecture: basic functional structure of a PLC system, including CPU functions, memory/storage, I/O interfaces, communication modules and power supply units.
• Interface/port models: typical interface diagrams and port descriptions for digital/analog inputs and outputs, communication ports, power and earthing connections.
• Module characteristics: principal characteristics of CPU, sensor/actuator interfaces, communication functions, HMI functions, programming/debugging/testing and documentation capabilities, and power‑supply behavior.
• Reliability and availability: high‑level guidance on availability, reliability and diagnostic features (self‑test, parity checking), while noting that system‑level functional safety is outside Part 1’s scope.
• Applicability: covers products that implement PLC functionality on dedicated hardware or on general‑purpose computers configured for industrial use.
• Normative links: references to other parts of the series - notably IEC 61131‑2 (equipment requirements and tests) and IEC 61131‑3 (programming languages).

Applications and users

IEC 61131‑1 is intended for professionals involved in industrial automation and control system design:

• Control engineers and system integrators selecting or specifying PLC systems
• PLC and peripheral manufacturers defining functional characteristics and marketing documentation
• HMI, PADT and field‑device designers ensuring interoperability with PLC architectures
• Test laboratories and procurement teams assessing compliance and compatibility
• Automation project managers and maintenance teams seeking consistent terminology and system models

By standardizing definitions and functional models, IEC 61131‑1 helps improve interoperability, procurement clarity and system documentation across manufacturing, process control and industrial automation projects.

Related standards

• IEC 61131‑2: Equipment requirements and tests (hardware tests, environmental and safety requirements)
• IEC 61131‑3: Programming languages (syntax, semantics, language mappings)
• Other IEC and national standards for electrical installation and safety (e.g., IEC 60364) for installation and safety practices

Keywords: IEC 61131‑1, PLC standard, programmable controllers, industrial automation, HMI, PADT, remote I/O, PLC architecture, programming languages.