Key Criteria for Selecting Industrial PLC Programming Languages

By LamXutai
3 min read
PLC Programming

In the evolving world of industrial automation, selecting the right PLC programming language is more than a technical preference—it is a strategic engineering decision that impacts scalability, efficiency, and long-term system performance. This article provides a practical, engineering-oriented guide for automation professionals seeking to align language choice with real-world industrial demands.

1. Performance Efficiency: Code Execution and Cycle Times When dealing with time-sensitive processes such as high-speed manufacturing or motion control, cycle time efficiency is critical. Languages like Structured Text (ST) often outperform graphical formats like Ladder Logic (LD) in executing complex math or conditional logic. For instance, in benchmarking tests, ST-based routines executed up to 30% faster in real-time processing scenarios.

2. Hardware Compatibility and Vendor Ecosystem Different PLC vendors support different language sets and execution models. For example, Siemens TIA Portal natively supports SCL (a variant of ST), while Allen-Bradley ControlLogix favors Ladder and Function Block Diagrams (FBD). Matching the programming language to the target hardware ensures better optimization, toolchain integration, and vendor support.

3. Team Expertise and Readability Engineering teams vary in their language fluency. Maintenance teams often prefer Ladder Logic for its visual clarity and alignment with traditional relay logic, while advanced developers may favor ST for algorithm-heavy applications. The chosen language should balance developer productivity and ease of maintenance.

4. Modularity and Code Reuse Languages that support modular design (e.g., ST and Function Blocks) allow reusable components, improving maintainability and reducing development cycles. In applications requiring version control and collaborative development, modular support is a must. Tools like Rockwell’s AOI and Siemens’ reusable blocks offer strong ecosystem-level modularity.

5. Standards Compliance and Interoperability Compliance with IEC 61131-3 ensures long-term viability across platforms. Moreover, as IIoT and Industry 4.0 systems demand interoperability, choosing languages that integrate well with OPC UA, MQTT, and RESTful APIs is essential. ST and FBD often provide better support for such integrations.

A Systematic Approach to PLC Language Comparison Rather than relying on ad hoc selection, engineers should follow a structured comparison approach:

  • Define system constraints (real-time speed, memory limits)
  • Assess team skills and long-term maintainability
  • Evaluate vendor roadmap and tool ecosystem
  • Score languages across use-case-specific benchmarks

Benchmarking for Real-World Deployment Engineers can establish baseline performance through practical metrics: average cycle time, memory footprint, debugging efficiency, and error traceability. For example, in a recent IIoT deployment, ST reduced program size by 40% compared to LD, enhancing performance on edge devices with limited RAM.

Use Case Spotlight: IIoT and Industry 4.0 Systems With distributed sensors and smart edge controllers becoming the norm, languages like ST or FBD shine in integrating with digital communication protocols and logic-heavy configurations. Ladder Logic may be limited in representing asynchronous workflows or protocol stacks, making it less ideal for Industry 4.0 deployments.

Mission-Critical Applications: From LD to ST In high-stakes sectors such as pharmaceuticals or aerospace manufacturing, code maintainability and deterministic behavior are paramount. Transitioning from LD to ST in these settings enables better abstraction, testability, and system diagnostics.

Future-Proofing Language Decisions Beyond syntax familiarity, engineers must consider long-term maintenance. Factors like backward compatibility, ecosystem health, community support, and training resources determine the future sustainability of a PLC language. Overlooking this can lead to the "maintenance trap"—where systems become fragile and difficult to evolve.

Conclusion Choosing the right PLC programming language requires more than comparing syntax and structure—it demands a holistic evaluation of performance, maintainability, interoperability, and real-world deployment needs. By adopting a systematic and future-facing approach, engineers can avoid costly rewrites and ensure that their automation systems remain robust, scalable, and aligned with Industry 4.0 evolution.