Factory and Site Acceptance Test, FAT and SAT
A factory acceptance test, FAT is the structured test of equipment or a control system at the vendor's premises before shipment. A site acceptance test, SAT repeats and extends that verification after installation at the plant. Both prove the system against the specification, the I/O list, and the functional design before it is accepted.
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Acceptance testing happens twice for a reason. At the factory acceptance test the system is exercised at the vendor's works with its inputs and outputs simulated or forced, so the control logic, the operator graphics, the alarms, and the sequences can be proven against the functional design and the I/O list before anything ships. Faults found here are cheap to fix because the engineers and the equipment are in one place. The site acceptance test then repeats the checks once the system is installed, but now against real field signals. Loops are checked end to end from the field device to the control system, integration with neighbouring systems is proven, and site conditions are accounted for. Punch items raised at the factory test are carried forward and closed at or before the site test. The I/O list and the cause-and-effect matrix are the documents both tests are run against, and IEC 62381 is the public standard that defines the factory, site, and site-integration tests for process-industry automation systems.
What a factory acceptance test verifies.
At the vendor's works the system runs with simulated or forced I/O so the control logic, operator graphics, alarms, interlocks, and sequences can be proven against the functional design and the I/O list. Because the people and the hardware are together, faults found at the FAT are the cheapest to correct.
What a site acceptance test verifies.
After installation the site acceptance test checks the system against real field signals. Loops are verified end to end from the field device through marshalling to the controller, integration with adjacent systems is proven, and conditions that only exist on site are accounted for. The SAT confirms the installed system behaves as the FAT predicted.
The I/O list and cause-and-effect basis.
Both tests are run against the same controlled documents. The I/O list defines every channel and its signal type, and the cause-and-effect matrix defines the interlock and trip logic. A test is only as complete as the register it is run against, so the I/O list has to match the installed scope.
Punch items, acceptance, and the standard.
Items raised at the factory test are logged and carried to the site test, where they are closed alongside any new site findings before acceptance. IEC 62381 defines the factory acceptance test, site acceptance test, and site integration test for automation systems in the process industry, giving both parties a common basis for what each test covers.
FAT versus SAT at a glance.
| Aspect | Factory Acceptance Test, FAT | Site Acceptance Test, SAT |
|---|---|---|
| Location | Vendor or integrator works, before shipment | Installed at the plant, after construction |
| Inputs and outputs | Simulated or forced | Real field signals, loop by loop |
| Main focus | Control logic, graphics, alarms, sequences | Loop checks, field integration, site conditions |
| Run against | Functional design and I/O list | Same, plus the as-installed plant |
| Timing | Before the system ships | After installation, before handover |
Frequently asked.
What is the difference between FAT and SAT.
A factory acceptance test is run at the vendor's works before shipment with simulated I/O, focused on logic, graphics, and sequences. A site acceptance test is run after installation against real field signals, focused on loop checks and integration. The FAT proves the build. The SAT proves the installation.
What documents are a FAT and SAT run against.
Primarily the I/O list, which defines every channel and signal type, and the cause-and-effect matrix, which defines the interlock and trip logic, alongside the functional design specification. The site test also checks against the as-installed plant.
Does a FAT replace a SAT.
No. A factory test cannot exercise real field wiring, field devices, or site integration, so a site acceptance test is still required after installation. The two are complementary stages, not alternatives.
What standard covers FAT and SAT.
IEC 62381 defines the factory acceptance test, site acceptance test, and site integration test for automation systems in the process industry. It gives vendor and owner a common basis for the scope and conduct of each test.
What is a loop check at SAT.
A loop check verifies a single instrument loop end to end, from the field device through marshalling and the I/O card to the control system display and any final element, confirming the signal reads correctly and the right channel is wired. It is a core part of the site acceptance test.