PLC Programming for Custom Machine Construction: Best Practices and Tips

PLC programming (Programmable Logic Controller) is the heart of every modern custom machine. Especially in custom machine construction, where no system is the same as another, flexible, clean, and future-proof programming is crucial for functionality, efficiency, and maintainability. In this blog post, we provide you with practical tips and proven methods to take your control programs to the next level.

1. Structured Program Design

A well-structured PLC program not only facilitates commissioning but also troubleshooting and later expansions. Therefore, use:

• Clearly named program blocks (FCs, FBs, OBs)
• Modular programming: e.g., separate blocks for axes, sensors, HMI, etc.
• Global constants and symbol tables to manage values centrally

2. Commenting and Documentation

• Documentation is often underestimated but saves time and nerves in the long run:
• Comments directly in the code: brief but clear
• Function description for each block

Overview of interfaces (inputs and outputs, variables)

This is especially essential for custom machines that are to be maintained or expanded later.

3. Use of Libraries and Standards

Use your own or manufacturer-provided libraries, e.g., for:

• Drive technology (Siemens DriveLib, SEW function blocks)
• Safety functions
• Communication (e.g., OPC UA, Modbus)

This saves time, increases quality, and ensures reusability.

4. Simulation and Testing on Site Avoid Errors

Use simulation functions (e.g., PLCSIM with Siemens) to test programs before loading them onto real hardware. This saves time during commissioning and helps eliminate major errors in advance.

5. Flexible Error Handling and Diagnostics

Implement clean error management from the start:

• Collective fault messages
• Acknowledgment logics
• Error history (FIFO memory, ring buffer)
• Plain text error messages for the HMI

This makes everyday work easier for operators and service technicians!

6. Practical Tip: Plan HMI and PLC Hand in Hand

Many programmers treat the HMI (user interface) separately from PLC programming. However, both sides benefit from:

• Common symbol names and structures
  
• Central text lists for error messages
• Status overviews for machine modes, cycles, etc.

An integrated approach leads to a coherent user experience.

Conclusion

PLC programming in custom machine construction is demanding but manageable with the right approach. Structure, reusability, simulation, and clean error handling are the keys to a maintenance-friendly and robust control program.

If you want to implement your PLC projects professionally or need support in control cabinet construction, feel free to contact us!