Underground mining equipment is expensive, difficult to access, and dangerous to commission in the field. A stoppable pump, fan starter, or auxiliary equipment unit that fails after going underground can take hours to recover, longer if the failure occurs during a production shift. The Factory Acceptance Test exists to catch these failures in the workshop, where they cost time instead of production.
FAT is standard practice across Queensland’s underground coal mines. What varies significantly is the thoroughness with which it is conducted. This article describes what a genuine FAT for underground mining equipment involves, and what is often missed.
What FAT is and what it is not
A Factory Acceptance Test is a structured, documented verification that equipment meets its specified requirements before leaving the manufacturer’s or integrator’s workshop. For PLC and HMI-based underground mining equipment, this means verifying that:
- The PLC program is the correct version, loaded correctly, and the processor is in the correct configuration for the specific equipment unit
- All I/O (digital inputs, digital outputs, analogue inputs, analogue outputs) are correctly wired and respond correctly to test signals
- HMI displays accurately reflect the PLC data they are connected to
- Operational sequences (start, stop, interlock, emergency stop) operate correctly
- Communications (between PLC and HMI, between PLC and network) operate correctly
- Equipment numbering, where the same program template is used for multiple similar units, has been correctly modified for the specific unit
FAT is not a rubber stamp. It is not signing a document that says the equipment looks correct. It is physically testing each I/O point, watching the HMI respond, stepping through operational sequences, and documenting the result of each test: pass, fail, or observation.
I/O testing methodology
I/O testing is the foundation of the FAT. For each input and output in the PLC, the test engineer:
- Identifies the I/O point from the I/O list and electrical schematics
- For digital inputs: applies a 24VDC signal to the input terminal (by bridging from a 24V supply or using a test tool), and verifies that the corresponding PLC tag changes state, both in the PLC program monitoring view and on the HMI if the tag is displayed
- For digital outputs: forces the output ON in program mode (or via a test function in the program), and verifies that the corresponding relay energises or indicator illuminates at the field terminal
- For analogue inputs: applies a simulated 4-20mA signal at the input terminal and verifies that the PLC tag reads the correct engineering value
- For analogue outputs: forces an analogue output value and verifies the correct mA signal at the output terminal
Each test result is recorded in the I/O function test sheet, typically a spreadsheet with one row per I/O point, columns for the test signal applied, the expected result, the actual result, and a pass/fail mark. This document is a formal project record.
An I/O test sheet that only records ‘PASS’ for every point without recording the specific test conditions and results is not a useful test record. If a failure occurs on site and the FAT test sheet is reviewed, ‘PASS’ with no supporting detail is meaningless. Record the test method, the expected value, and the actual value for each point.
HMI and sequence testing
After I/O testing is complete, HMI and sequence testing verifies the operational logic:
- Navigate each HMI screen and verify that all displays, indicators, and control elements are present and correctly labelled
- Verify that analogue values displayed on the HMI match the values in the PLC, particularly for safety-critical measurements such as gas levels, temperatures, and pressures
- Step through each operational sequence (start, run, stop) and verify that the sequence progresses correctly through each step
- Test each interlock: verify that when an interlock condition is simulated, the correct response occurs (trip, inhibit, alarm, or other)
- Test emergency stop: verify that the E-stop circuit de-energises the correct outputs and that the SCADA or HMI reflects the E-stop state correctly
Equipment numbering
At mines like Anglo American’s Moranbah North, where the same equipment type (auxiliary fan starters, pod pumps) goes through regular overhauls, the same PLC program template is used for each unit. The equipment number in the program, the identifier that links the unit to the site SCADA and tracking systems, must be correctly updated for each unit before the FAT.
A fan starter programmed as AF001 that is actually AF011 will load and pass a FAT without anyone noticing, until it is underground and the SCADA operator cannot find it because the asset tag doesn’t match the SCADA display. This is a common error that FAT should catch, and it is only caught if the equipment number is explicitly checked against the site’s equipment register as part of the FAT scope.
Documentation deliverables
The standard FAT deliverables for underground mining equipment:
- Completed I/O function test sheet, signed and dated by the test engineer
- FAT report: a summary of the test conducted, the equipment tested, the date, and any non-conformances raised and resolved
- Program backup: the exact program version that passed the FAT, retained as the baseline for site installation
- Any calibration records for analogue I/O that was calibrated during the FAT
About the author
Dennis Murphy RPEQ has conducted Factory Acceptance Tests for underground mining equipment across Anglo American’s Moranbah North and Aquila mines, Oracle Industries’ Carborough Downs programme, and other Bowen Basin mine sites. Contact: [email protected]