The situation
PI Technical Services required PLC firmware upgrades, HMI updates, and full Factory Acceptance Testing for a shotcrete machine destined for underground coal mining operations. Shotcrete machines are used in underground coal mines to spray concrete onto tunnel walls and roofs for ground support. Reliability is critical given the environment they operate in. The controller was an Allen Bradley Micro800 series, the task was to bring the firmware current, update the HMI, and verify the complete system before site dispatch.
Our approach
- Reviewed electrical schematics and mapped I/O across digital input, digital output, and analogue modules.
- Upgraded the Micro800 PLC firmware and updated the Schneider Magelis HMI program to the current version.
- During FAT, encountered a persistent communication fault on the HMI: “The PLC equipment has returned error code 02H”. Standard checks, network cabling, IP configuration, Modbus driver setup, device mapping, all appeared correct.
- Diagnosed the root cause: the upgraded Micro800 firmware introduced a requirement for contiguous Modbus register addressing. Gaps in the mapped register space caused the PLC to return invalid responses, even though the underlying code was unchanged.
- Added dummy tags to fill unused register gaps and ensure a continuous Modbus address range.
- Communications stabilised immediately. Proceeded to complete full Factory Acceptance Testing: I/O verification, functional testing, HMI navigation and alarm verification, E-stop and interlock testing, PLC/HMI data accuracy cross-check.
- Delivered commissioning test sheets and program backups.
Outcome
The shotcrete machine was fully updated, the Modbus fault resolved, and the system factory acceptance tested before site dispatch. PI Technical Services received complete FAT commissioning test sheets and program backups, a verified baseline for underground coal mine site commissioning and ongoing maintenance.
The key lesson from this job: same code doesn’t always mean same behaviour after a firmware upgrade. The Micro800’s new contiguous addressing requirement wasn’t obvious from the error message, and would have caused a fault on site if it hadn’t been caught during FAT.