In today’s high-stakes industrial automation environment—where downtime is expensive, skilled labor is scarce, and global standardization is critical—your PLC software architecture matters more than ever. The latest Siemens TIA Portal V21 release (November 2025) provides a powerful platform for structured, modular, and scalable programming rooted in IEC 61131-3 principles. Although not a pure object-oriented environment like C++ or Java, TIA Portal’s Structured Control Language (SCL) and its advanced Function Block (FB) architecture enable engineers to apply the most valuable OOP concepts directly to PLC development.
For plant managers, project managers, and engineering leaders, applying these principles means lower engineering effort, faster commissioning, fewer errors, and a globally standardized automation strategy—whether you’re deploying a wastewater plant across continents or modernizing a packaging line with 200+ devices.
This guide focuses on what truly works in real-world industrial PLC development: Encapsulation, and Abstraction as essential tools; Inheritance and Polymorphism as optional techniques used sparingly and strategically.
Why OOP Principles Matter in Industrial Automation
Industrial automation systems are becoming larger, more integrated, and more software-driven. Traditional monolithic ladder logic simply cannot support the scale and long-term maintainability required for modern S7-1500 and S7-1200 applications. OOP principles, applied appropriately, deliver:
- Modularity – breaking complex plants into reusable building blocks
- Scalability – rapidly deploying standardized logic across multiple units, lines, or facilities
- Maintainability – easier troubleshooting and safer upgrades
- Team collaboration – enabling global engineering teams to work in parallel
- Reduced commissioning time – through standardized interfaces and repeatable control modules
TIA Portal V21 strengthens these capabilities with SCL improvements, better OT/IT connectivity, optimized access, and streamlined engineering workflows—without altering the core OOP-inspired programming model built since V14/V15.
The Tools: IEC 61131-3 Constructs That Enable OOP-Style Design
TIA Portal implements OOP-like behavior through the following standard elements:
- Function Blocks (FBs) — the closest equivalent to classes
- Instance Data Blocks (IDBs) — persistent memory: each “object” has its own state
- User-Defined Data Types (UDTs) — standardized data structures
- SCL Methods, Static Variables, and Structured Interfaces — behavior + data packaged together
- Optimized Access — ensuring proper encapsulation and symbolic access
Newer Siemens technologies such as SIMATIC AX even support true OOP (classes, EXTENDS, interfaces), with libraries imported into TIA Portal as standard FBs.
OOP Principle #1 — Encapsulation (Essential)
The foundation of all modern Siemens PLC programming
Encapsulation bundles data and logic into a single, self-contained module. In TIA Portal, this is implemented natively through Function Blocks (FBs) and their Instance Data Blocks (IDBs).
How Encapsulation Works in TIA Portal
- Each device—motor, valve, pump, PID loop—is implemented as an FB.
- Each instance in your project creates its own IDB with unique parameters, timers, states, and faults.
- Inputs/Outputs define the contract; internal logic and static variables remain hidden.
- With Optimized Block Access, external code cannot modify IDB memory directly, enhancing reliability and safety.
Industrial Benefits
- Plug-and-play scalability: Build a Motor FB once, reuse it for 200 motors.
- Faster troubleshooting: A technician can inspect the IDB for “Pump_101” and see all relevant data at a glance.
- Clear division of work: Multiple engineers can develop and test separate FB libraries without conflicts.
- Improved safety and uptime: Encapsulated logic prevents accidental cross-interactions between devices.
If your PLC software isn’t using encapsulation systematically, it isn’t modern, maintainable, or scalable.
OOP Principle #2 — Abstraction (Essential)
Simplify complexity, standardize interfaces, and future-proof your system
Abstraction hides complex internal logic behind a clean, predictable interface.
How Abstraction Works
- UDTs group commands, statuses, and configuration data for each device type.
- FB Interfaces (IN/OUT/IN_OUT) expose only what operators or higher-level logic need.
- Layered architecture:
- Device Control (motors, valves, drives)
- Unit/Area Control (mixing tanks, conveyors, skids)
- Supervisory Control (recipes, sequencing, line control)
An operator or upper-level block interacts with a simple interface like:
Start
Stop
SpeedSetpoint
FaultStatus
—not the dozens of internal calculations, filtering, safety bits, or PROFIdrive telegrams behind it.
Industrial Benefits
- Hardware flexibility – swap a drive vendor by updating one FB.
- Cleaner HMI and SCADA integration – consistent UDTs mean consistent data mapping.
- Easier global standardization – one unified interface for every asset across every plant.
Abstraction reduces cognitive load, speeds commissioning, and creates durable automation architectures.
OOP Principle #3 — Inheritance (Use Rarely)
Supported in SIMATIC AX, simulated in TIA Portal—generally avoided in industrial practice
Inheritance enables a derived block to reuse or override logic from a base block.
In TIA Portal STEP 7:
- True inheritance is not natively supported.
- It can be emulated via composition, or implemented via SIMATIC AX externally.
Why It’s Rarely Used in Industry
- Fragile hierarchies—changing a base block can break dozens of derived blocks.
- Harder for maintenance teams—most technicians don’t think in terms of inheritance trees.
- Composition is safer and clearer.
When It Is Useful
- Large OEM libraries with well-controlled development teams
- Architectures generated automatically using TIA Openness
- Advanced software built in SIMATIC AX with true EXTENDS, then imported into TIA Portal
Unless you have a strong software engineering team and a need for true inheritance, avoid it.
OOP Principle #4 — Polymorphism (Specialized Use Only)
Possible through interfaces in SIMATIC AX or CASE statements in SCL — but rarely needed
Polymorphism allows different objects to respond to the same command differently.
In TIA Portal
Polymorphism is typically emulated using:
- A Type ID inside a UDT
- A centralized CASE statement switching behavior based on the device type
- Or by passing different IDBs into the same generic FB (“data-driven polymorphism”)
Industrial Reality
- Works, but centralizes too much logic in one place
- Changes require extreme care and strict version control
- Often replaced by simpler, more maintainable design patterns
Use polymorphism only when absolutely necessary.
Practical Summary for Industrial PLC Development
| OOP Principle | Industrial Viability | Recommendation |
|---|---|---|
| Encapsulation | ESSENTIAL | Use everywhere. Every device = an FB. |
| Abstraction | ESSENTIAL | Design simple, clean interfaces; hide complexity. |
| Inheritance | AVOID (except AX) | Prefer composition; use AX or Openness if required. |
| Polymorphism | AVOID (niche use) | Use only when no simpler structure works. |
A good test:
“Will a technician understand and fix this quickly at 3 AM?”
Encapsulation, Abstraction, and Composition pass.
Inheritance and Polymorphism usually don’t.
Real-World Example: Global Pump Library
Imagine deploying wastewater treatment plants worldwide. Using OOP principles:
- Encapsulation: A Pump FB stores its own runtime, alarms, start/stop logic.
- Abstraction: Its interface stays the same everywhere.
- Composition: A Tank FB includes multiple Pump FBs, Valve FBs, and PID FBs.
- Optional polymorphism: Different pump technologies selected via device type in a shared Pump FB.
Result:
Fast rollout, consistent quality, easy troubleshooting, and scalable automation across continents.
Conclusion: Build Future-Proof, Modular, Maintainable PLC Software
Transitioning from monolithic ladder logic to structured SCL-based, modular design in TIA Portal V21 is a strategic advantage for any large-scale industrial project. With the right architecture:
- Engineering becomes faster.
- Maintenance becomes safer.
- Global standardization becomes achievable.
- Commissioning time drops dramatically.
Whether you’re modernizing a plant or deploying a global automation framework, leveraging encapsulation, abstraction, and composition delivers measurable ROI.
We Build World-Class Modular PLC Architectures
As global PLC program structuring specialists, we help engineering teams and industrial companies:
- Develop modular FB/UDT-based control libraries
- Standardize automation across multiple sites
- Implement SCL-based architectures that scale
- Integrate SIMATIC AX for advanced OOP when needed
- Generate large repetitive systems using TIA Openness
- Modernize legacy programs with maintainable structures
Ready to transform your automation with professional OOP-based PLC programming?
Contact us today for a consultation.
