FAT (Factory Acceptance Test)
A factory acceptance test (FAT) is a formal check that a machine, skid, cell, or control package meets the agreed specification before the buyer treats that package as ready for ship or site install. The test runs against a written procedure with expected results. Buyers and suppliers use the record as part of acceptance, punch-list closeout, and version control for the software and configuration that will travel with the asset.
Plant teams care because FAT is often where a capital program stamps controls and sequence work "done." That stamp can honestly close a digital twin prototype slice, including virtual commissioning finds. It does not by itself create an operational digital twin of the running hall after go-live.
Key Components
Agreed scope and procedure - Which sequences, interlocks, alarms, and variants are in the test, and what pass looks like.
Controller and HMI under test - The production-intended PLC program and HMI screens, not a throwaway demo.
Physical or virtual plant response - Real hardware on the supplier floor, or a modeled plant that answers I/O so sequences can run before the cell is assembled.
Punch list and version record - Open items, retests, and the software version that passed so site work starts from a known baseline.
Applications in Manufacturing and Logistics
Machine builders and integrators use FAT before shipment so handshake faults, interlock deadlocks, and HMI mistakes show up in the shop rather than during the install outage. Virtual FAT runs the same idea against a simulation model so software and sequence proof can start while mechanical build is still incomplete. Logistics and material-handling projects use the same gate for conveyor merge logic, routing rules, and emergency-stop recovery before the network is live on site.
After FAT, site acceptance and physical commissioning still prove wiring, device addressing, calibration, mechanical response, and safety timing the model or supplier floor could not cover. The twin handoff question is separate: keep the prototype sandbox if useful, and fund the live instance when shift visibility, the spatially oriented dataset, and pattern work are in scope.
Benefits and Challenges
The benefit is moving reachable software and sequence faults earlier, shortening the critical path of onsite debug, and leaving a clear acceptance record. Virtual FAT can start weeks before physical hardware is ready and still feed the same punch list into the physical pass.
The challenge is treating a green FAT as proof the plant already owns a synchronized twin of operations. FAT closes supplier or prototype acceptance. Live logistics reaction, stored place-and-time history, and correlation and causality analytics after start-up need a separate instance budget. Models also miss soft materials, wiring mistakes, and analog dynamics, so physical tests stay mandatory for those classes of risk.
Related Terms
Virtual commissioning is the broader practice of testing controls against a plant model. FAT is one formal acceptance gate inside or after that work. Digital twin prototype is the academy subtype that covers pre-physical design and sequence proof. System integration and site commissioning continue after the package leaves the supplier. An operational digital twin is the live hall layer that begins only once physical assets and plant signals exist to sync.
Frequently Asked Questions
Does a virtual FAT replace a physical FAT? No. Virtual FAT shortens and de-risks software and sequence proof. Physical FAT or site tests still cover hardware, wiring, calibration, and safety response the model cannot prove honestly.
Is FAT the same as virtual commissioning? Related, not identical. Virtual commissioning is the ongoing test method. FAT is a witnessed acceptance event against a procedure, which may be virtual, physical, or both.
Can the twin program close at FAT? The prototype slice can. Live shift monitoring, the spatially oriented dataset, and correlation work after go-live cannot close on that stamp alone unless the roadmap explicitly leaves them out of scope.
Who usually owns FAT? Supplier engineering and the buyer's controls or project team own the acceptance gate. Operations owns whether an operational twin is funded after install.