Every wiring error or logic bug found in the vendor workshop costs a fraction of the same fault found during plant start up. A structured test before shipping catches those faults while engineers, simulators and spare parts are all in one room.
Control systems are assembled and configured in the supplier factory, then shipped to site. A formal test in the factory proves the hardware and software meet the specification before anything leaves the building.
What Is a Factory Acceptance Test?
A factory acceptance test, or FAT, is a formal test of a control system at the supplier facility, witnessed by the owner, to prove that hardware, software and documentation meet the agreed specification before shipment. It covers the full system, from I/O cards to engineering and operator stations.
Just Measure It explains that FAT is done at the manufacturer with the owner and often a third party, before the equipment ships. SAT follows at site once installation is complete.
IEC 62381, updated in 2024, defines FAT, SAT and site integration testing for automation systems in the process industry. Many contracts reference it directly.
For large DCS projects, FAT can last several weeks and include operators from the plant.
FAT vs SAT vs SIT
| Test | Where | Focus |
|---|---|---|
| FAT | Supplier factory | Hardware, software and logic against specification |
| SAT | Plant site | Installation, power, field wiring, communication |
| SIT | Plant site | Integration with third party systems and packages |
SAT is followed by loop checks, described in cold and hot loop testing. Together they complete the path to commissioning.
Faults found at site are costly because crews, cranes and schedules are waiting. That is why a thorough FAT pays back quickly.
8 Proven Factory Acceptance Test Steps
Redundancy tests should pull a controller, a network cable and a power supply while the process simulation runs. Watch for bumpless switchover, as explained in DCS controller redundancy.
Network failover is tested the same way for ring and dual networks. Record the switchover time for each test.
Punch List Categories
Must be fixed before shipment.
Fix before or during SAT.
Minor, fix when convenient.
Every item needs an owner, a due date and a retest record. The FAT certificate is signed only when category A items are closed.
Graphics are checked against the HMI philosophy, often based on ISA 101. Operator involvement at this stage catches usability issues early.
How the Test Is Organised
Simulation tools let the team run sequences without field devices. Tie back simulation is common for interlock and loop testing.
Duration Estimate
Example:
1200 I/O at 3 min each = 60 h
150 loops and sequences at 20 min each = 50 h
Graphics, alarms and redundancy = 40 h
Total 150 h, about 19 days at 8 hours per day
Add time for punch fixes and retests, often 20 percent. Plan the schedule with the client witness team early.
Duration Calculator
Parallel test teams can shorten the calendar time, as long as simulation stations are available.
- Finds faults before site.
- Trains client engineers.
- Reduces start up risk.
- Clear contractual milestone.
- Testing only a sample of I/O.
- No redundancy failure tests.
- Unapproved test procedure.
- Closing punch items without retest.
For safety systems, the same idea supports validation in the SIS safety lifecycle.
IEC 62381 FAT SAT SIT PDF
How to Conduct FAT Video
Factory Acceptance Test FAQ
Related Articles
- Distributed Control System
- DCS Controller Redundancy
- Cold Loop and Hot Loop Testing
- DCS Components ES, OS and AS
- DCS Migration and Obsolescence
External References
What We Learn Today
- A factory acceptance test proves the system before it ships.
- Test every I/O point, loop, graphic and redundancy path.
- Close category A punch items before signing the FAT certificate.