On-Site Commissioning: What Happens After the FAT
The Factory Acceptance Test (FAT) is complete. The system ran through its cycles in the workshop, the client witnessed it, the punch list was closed out. Now it needs to work in the real world, connected to real services, real networks, and real production demands.
On-site commissioning is where the engineering meets reality. It is also where most schedule overruns happen if the groundwork has not been done properly.
Arrival and Installation Support
Before any controls work begins, the mechanical and electrical installation must be complete and verified. In practice, the commissioning engineer often arrives to find cables still being pulled, pneumatic supplies not yet connected, or network infrastructure incomplete.
We always issue a site readiness checklist before mobilising. It covers power supplies (confirmed voltage, phase, and capacity), network infrastructure (switches, patch panels, IP addressing), pneumatic and hydraulic supplies, and mechanical installation sign-off. Starting commissioning before these items are confirmed wastes time and money for everyone.
Power-On and I/O Verification
The first commissioning task is a controlled power-on sequence. Each circuit is energised individually with loads disconnected where appropriate. Supply voltages are verified. Earth fault loop impedance is checked.
Once power is confirmed, every I/O point is verified. Every sensor, every actuator, every motor starter. The I/O list from the design phase becomes the commissioning checklist. Each point is forced or stimulated and confirmed against the PLC programme. This is methodical, often tedious, and absolutely essential. Faults found at I/O check are simple to fix. The same faults found during integrated testing are much harder to diagnose.
Site Acceptance Testing (SAT)
The SAT follows the same test protocol as the FAT, but on site with production-representative conditions. The system runs its sequences with actual parts (or representative samples), actual cycle times, and actual interface connections to upstream and downstream equipment.
SAT testing typically reveals integration issues that were not visible in the workshop. Network communication timing, interaction with existing plant systems, environmental factors (temperature, vibration, electrical noise), and operator workflow all affect system behaviour in ways that a workshop FAT cannot fully replicate.
We document every issue found during SAT, categorise it by severity, and work through the list systematically. Critical items that prevent safe operation are resolved before proceeding. Non-critical items are added to a punch list with agreed timescales for closure.
Fault-Finding and Optimisation
Even with thorough FAT and SAT testing, the first days of production running will expose issues. Sensor positions may need fine-tuning. Cycle times may need optimisation. Alarm thresholds may need adjustment based on actual process variation.
This is normal and expected. We allocate time in the commissioning programme for production support and optimisation. The goal is to hand over a system that runs reliably at the target OEE, not one that technically works but needs constant attention.
Documentation and Training
Commissioning does not end when the machine is running. The handover package must include updated as-built drawings (reflecting any changes made during commissioning), final PLC programme backups, HMI screen documentation, operating procedures, and maintenance schedules.
Operator and maintenance training is delivered on site during commissioning. We cover normal operation, fault diagnosis, routine maintenance, and recovery procedures. Training people on the actual equipment, in the actual environment, with the actual HMI screens is far more effective than sending a manual.
The Handover
A formal handover meeting documents that all SAT criteria have been met, all training has been delivered, all documentation has been provided, and any outstanding punch list items have agreed completion dates. Both parties sign off, and the system becomes the client's responsibility.
Clean handovers require clean commissioning. There are no shortcuts.