Tech & Project Insights

Beetle Engineering & Automation recently completed Factory Acceptance Testing (FAT) of a shotcrete machine at P.I. Technical Services.

The project initially involved a PLC hardware and firmware upgrade, with only minor code changes expected to suit updated wiring. However, once we moved into FAT, it became clear the job would demand more detailed investigation.

My role focused on the PLC and HMI implementation, along with I/O validation and functional testing during FAT.

FAT Testing in Action

FAT is where systems are proven before they ever reach site. It is also where hidden issues tend to surface.

During testing, we encountered a persistent fault on a Schneider Magelis HMI:

“The PLC equipment has returned error code 02H”

At first glance, it appeared to be a standard communications issue.

We worked through the usual checks:

• Network cabling
• IP configuration
• Modbus driver setup
• Device mapping

Everything looked correct, yet the fault remained.

Root Cause Identified

The issue was not physical or configuration-related. It was tied to a behavioural change in the Allen Bradley Micro800 series following the upgrade.

The newer Micro800 controllers require contiguous Modbus addressing. If gaps exist in the mapped register space, the PLC can return invalid responses.

That is exactly what was happening here.

The Fix

Once identified, the fix was straightforward:

• Fill unused Modbus register gaps with dummy tags
• Ensure the Modbus address range is fully continuous

After implementing this, communications stabilised and the HMI fault cleared during FAT.

Why This Matters

FAT plays a critical role in catching these types of issues early. Resolving them in a controlled workshop environment avoids delays and risk during site commissioning.

This project reinforced an important lesson:

“Same code” does not always mean “same behaviour,” especially after firmware or controller upgrades.

Final Stages

With the Modbus issue resolved, the system moved into final proving and tidy-up. This stage ensures the machine is ready for reliable operation in underground mining conditions.

Acknowledgements

This was a strong team effort on the floor at P.I. Technical Services. Thanks to:

• Brooke, Graham, and Scotty for their electrical expertise
• Rockwell Automation and Schneider Electric support teams
• Remtron for technical assistance
• Reinach van Nieuwenhuizen for ModbusForge, which helped isolate the issue
• Scott Single and Riaan Swanepoel for providing Micro820 hardware for testing

Need Help With FAT or PLC Upgrades?

Beetle Engineering & Automation supports FAT, commissioning, and troubleshooting across PLC, HMI, and industrial communication systems.

If you are experiencing Modbus issues after a Micro800 upgrade, reach out. Happy to share what we learned.