PLC's object-oriented programming - Database & Sql Blog Articles

Probe domestic switch needle KG-300K needle head diameter is 3.0mm normally open switch needle

Photocoupler

Object-oriented programming (OOP) represents a powerful paradigm in high-level computer programming, and its principles can be adapted into industrial control systems like PLCs. Although full object-oriented features such as "inheritance" are not directly supported in most PLC languages, the fundamental concept of OOP—using classes and objects—can still be applied effectively. In this context, a class can represent a specific control object, such as a motor or valve, while an object is an instance of that class, allowing for modular and reusable code.

Siemens' Step7 and Schneider's Unity are two widely used PLC programming environments that support object-oriented approaches. In Step7, function blocks (FBs) act as the equivalent of classes, encapsulating logic, data, and behavior. Each FB can have a background data block (DB), which serves as the instance (object) of that class. This structure enables multiple instances of the same control logic to be created, each with its own set of parameters and state variables. Similarly, in Unity, the DFB (Dynamic Function Block) provides a way to define reusable components with inputs, outputs, and internal variables, aligning closely with OOP concepts.

The distinction between structured programming (like FC blocks in Step7) and object-oriented programming lies in how logic is organized and reused. Structured programming focuses on functions and procedures, while OOP emphasizes encapsulation, abstraction, and modularity. This difference mirrors the contrast between C and C++ in computer programming, where C++ introduces classes and objects to enhance code organization and reusability.

Implementing object-oriented programming in PLCs requires careful planning of the system architecture. A well-designed electrical structure—such as layers for automation, engineering, and functional groups—can significantly enhance the effectiveness of OOP. Each control object, such as a motor or valve, should be modeled as a class, encapsulating all relevant inputs, outputs, and status information. This approach allows for standardized, maintainable, and scalable control systems.

One of the key advantages of OOP in PLC programming is standardization. By creating a library of reusable function blocks, developers can reduce redundancy and improve consistency across projects. Standardized libraries also enable junior programmers to focus on application design rather than low-level implementation, freeing experienced engineers to work on more complex tasks. This division of labor not only increases efficiency but also supports long-term career growth and knowledge retention within the industry.

Another benefit is improved reusability and manageability. Function blocks with independent data storage (like FBs in Step7) are easier to reuse across different projects without causing conflicts. This independence reduces the risk of errors and simplifies debugging. While some PLC platforms lack built-in support for OOP-like structures, alternative solutions such as FC + Shared DB can be used, though they sacrifice some level of modularity and flexibility.

Finally, object-oriented programming promotes a more intuitive and maintainable approach to PLC development. By organizing code around real-world control objects, it becomes easier to associate schematic diagrams with program logic. This clarity helps both developers and maintenance personnel understand and troubleshoot systems more efficiently. Whether using pre-built function blocks or custom designs, the goal remains to create clean, efficient, and reliable control programs that meet project requirements.

In conclusion, adopting object-oriented programming in PLC development offers significant benefits in terms of standardization, reusability, and maintainability. As the field of industrial automation continues to evolve, embracing these modern programming practices will help companies build more robust and scalable systems. It's time to move beyond traditional methods and embrace a more structured, efficient, and future-ready approach to PLC programming.