Picture this: it’s your first week on the factory floor, and a senior engineer hands you a printed ladder diagram the size of a wall poster. “You need to understand this by Monday,” he says, walking away. That was my introduction to PLC programming — and honestly, it felt like being handed a map written in a language I’d never seen before.
Fast forward to today, and IEC 61131-3 has become the universal language of industrial automation. Whether you’re commissioning a Siemens SIMATIC S7 in a German automotive plant, programming an Allen-Bradley ControlLogix at a food processing facility in Ohio, or configuring a Mitsubishi MELSEC line in a Japanese semiconductor fab — the same standard governs the logic underneath. Let’s think through this together, because once you truly grasp IEC 61131-3, the entire world of PLC programming opens up.
What Exactly Is IEC 61131-3 — And Why Should You Care?
IEC 61131-3 is the third part of the IEC 61131 international standard, published by the International Electrotechnical Commission. It defines five programming languages for Programmable Logic Controllers (PLCs), creating vendor-neutral portability and reducing training overhead across different industrial platforms.
Before this standard, every PLC manufacturer had its own proprietary programming environment. Migrating from one brand to another meant retraining entire engineering teams from scratch. The IEC 61131-3 standard, first released in 1993 and significantly updated in its current 3rd edition (2013, with 2026 implementation guidance now widely adopted), changed all of that.
The Five Programming Languages: A Deep Dive
Here’s where it gets genuinely fascinating — and this is the part most beginners skip over too quickly. Each language isn’t just a stylistic choice; it’s a cognitive tool shaped for different types of automation logic.
- Ladder Diagram (LD): The most widely used language globally, LD mimics the relay logic diagrams electricians already understood in the 1960s. Contacts and coils are arranged on “rungs” between two vertical power rails. If you’re working in North America or maintaining legacy systems, you’ll encounter LD constantly. Think of it as the Excel of PLC languages — not always the most elegant, but universally understood.
- Function Block Diagram (FBD): A graphical language where pre-built functional blocks (like PID controllers, timers, counters) are connected via signal flow lines. FBD is enormously popular in process industries — oil & gas, water treatment, chemical plants — because it visually mirrors how process engineers think about signal flow. Siemens TIA Portal and CODESYS both leverage FBD heavily.
- Structured Text (ST): This is the high-level text language of IEC 61131-3, syntactically similar to Pascal or Ada. ST is where PLC programming truly meets software engineering. It supports loops, conditional statements, user-defined data types, and object-oriented features introduced in the 3rd edition. In 2026, ST is experiencing explosive growth as software-defined automation (SDA) becomes mainstream.
- Instruction List (IL): An assembly-like low-level text language. Historically used when memory was scarce, IL has been officially deprecated in the 3rd edition of the standard. You’ll still find it in older systems, but no new projects should be built on it.
- Sequential Function Chart (SFC): Based on Grafcet methodology, SFC is designed for sequential processes — think: step 1, then step 2, with transitions and divergences. Bottling plants, CNC machine tool sequences, and automated assembly lines are natural fits. SFC is arguably the most readable language for describing complex multi-step processes to non-engineers.
Real-World Applications: From Stuttgart to Singapore
Let’s ground this in actual industrial reality, because theory without context doesn’t stick.
Volkswagen’s Zwickau EV Plant (Germany): One of Europe’s most automated vehicle assembly facilities relies heavily on FBD and SFC in its KUKA robot coordination systems. The visual clarity of FBD allows cross-functional teams — mechanical, electrical, and controls engineers — to communicate around the same programming artifacts without language barriers.
Procter & Gamble’s Manufacturing Network (USA): P&G has been a documented advocate of CODESYS-based ST programming for standardizing logic across global facilities. A controller program written in ST in Cincinnati can be reviewed, modified, and validated by an engineer in Warsaw or Manila — the language is the common ground.
Samsung SDI Battery Gigafactory (South Korea): With the battery manufacturing boom of 2024–2026, facilities like Samsung SDI’s Hungarian and Korean plants use SFC extensively for managing the precise sequential steps in electrode coating and cell assembly processes, where a single missed transition can mean scrapping an entire batch.
Yokogawa DCS Integration (Japan/Global): Yokogawa’s CENTUM VP distributed control system supports IEC 61131-3 FBD natively for process control applications, allowing oil refinery engineers to design and simulate PID loops before deployment — dramatically reducing commissioning time.
Structured Text in 2026: The Language Taking Over
If you only have bandwidth to master one IEC 61131-3 language for your career trajectory in 2026, make it Structured Text. Here’s the reasoning:
- The rise of IIoT (Industrial Internet of Things) and edge computing demands more complex data processing logic than LD or FBD can elegantly handle.
- Object-Oriented Programming (OOP) features in ST (classes, inheritance, interfaces) — part of the Edition 3 specification — are now natively supported in CODESYS 3.5, Siemens TIA Portal V18+, and Beckhoff TwinCAT 3, enabling software architecture practices from IT to migrate into OT (Operational Technology).
- Version control with Git is infinitely more practical with text-based ST code than with graphical LD or FBD files.
- The growing overlap between PLC engineers and software engineers makes ST the bridge language for multidisciplinary teams.
Choosing the Right Language: A Decision Framework
Rather than prescribing one-size-fits-all advice, let’s think through your specific situation:
- If you’re an electrician transitioning to automation: Start with LD. The conceptual bridge from relay logic is natural, and you’ll be productive quickly.
- If you’re in process control (chemical, oil & gas, water): FBD is your primary tool, with SFC for batch processes (aligned with ISA-88 batch standard).
- If you’re building reusable function libraries or complex motion control: ST is non-negotiable. Invest the time.
- If you’re documenting or communicating sequences to operations teams: SFC provides the clearest visual narrative of any of the five languages.
- If you encounter IL in legacy code: Learn to read it for maintenance purposes, but plan a migration path to ST or LD in your next project cycle.
Tools & Development Environments Worth Knowing in 2026
The standard is hardware-agnostic, but the tooling matters enormously for productivity:
- CODESYS V3.5 SP20+: The de facto open runtime used by hundreds of OEM hardware vendors (Wago, Schneider, IFM, and more). Free IDE, excellent ST support, and a growing library ecosystem.
- Siemens TIA Portal V19 (2026): The industry benchmark for large-scale manufacturing. All five IEC languages supported, with SCL (Structured Control Language) as Siemens’ ST dialect.
- Beckhoff TwinCAT 3: Built on Visual Studio, offering full .NET integration with ST. The preferred choice for high-precision motion control and robotics in 2026.
- Rockwell Studio 5000 Logix Designer: Dominant in North American discrete manufacturing. LD is primary, but ST support has been strengthened in recent releases.
- ABB Automation Builder / Mendix low-code integration: Emerging trend in 2026 where low-code platforms sit above IEC 61131-3 runtimes, enabling non-engineers to configure parameters while ST handles the underlying logic.
Realistic Learning Path: From Zero to Productive
Here’s an honest, time-bound roadmap rather than an idealized curriculum:
- Weeks 1–3: Install CODESYS (free). Complete the official Getting Started tutorials. Write your first LD program: a simple motor start/stop with interlocks.
- Weeks 4–8: Build the same program in FBD and then ST. Understand the conceptual translation. Add a timer and counter to each.
- Months 3–4: Tackle SFC. Model a 5-step sequential process (conveyor → sensor detect → actuate → verify → reset). This is where real-world thinking kicks in.
- Months 5–6: Introduce OOP in ST. Build a reusable Function Block for a pump controller with methods and properties. This alone puts you ahead of 80% of practicing PLC engineers.
- Ongoing: Study real programs from open-source repositories on GitHub (search: CODESYS IEC 61131-3 examples). Real code teaches what tutorials cannot.
One realistic alternative worth considering: if you’re coming from a software engineering background and find the graphical languages cognitively cumbersome, it’s entirely valid to focus exclusively on ST first and learn the graphical languages reactively when job requirements demand it. The standard doesn’t mandate a learning sequence — your career context should.
Conversely, if you’re an experienced electrician who finds ST intimidating, that’s completely fine in 2026. Excellent careers are built on LD mastery alone — especially in maintenance, commissioning, and field service roles where LD remains the dominant diagnostic language on the shop floor.
Editor’s Comment : IEC 61131-3 is one of those rare industrial standards that genuinely rewards the time you invest in understanding it deeply. The five languages aren’t competitors — they’re a toolkit, and the best automation engineers I’ve met don’t debate which language is “best.” They ask, “Which language makes this problem most readable, maintainable, and safe?” That question will serve you better than any certification ever will. Start with one language, build something real, break it deliberately, fix it — and then move to the next. The standard has been the backbone of industrial automation for over three decades, and with software-defined manufacturing accelerating in 2026, its relevance has never been greater.
태그: [‘IEC 61131-3’, ‘PLC programming languages’, ‘Structured Text PLC’, ‘industrial automation 2026’, ‘CODESYS tutorial’, ‘ladder diagram basics’, ‘PLC programming guide’]
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