FAT, SIT and SAT — acceptance testing of automation systems
What factory and site acceptance tests cover, how they relate to integration tests and loop checks (IEC 62381/62382), and a practical checklist with documentation tips.
Acceptance tests show that the automation system meets its specification before it controls the real process. IEC 62381 describes four test stages and their checklists.
The stages
| Test | Where | Purpose |
|---|---|---|
| FAT — factory acceptance test | Supplier's workshop | Hardware and software against the specification, usually with simulation |
| FIT — factory integration test | Workshop | Interfaces between several subsystems (DCS ↔ PLC packages, SIS) |
| SAT — site acceptance test | Site, after installation | System works with the real installation and infrastructure |
| SIT — site integration test | Site | Integration of all subsystems on site |
Loop checks (IEC 62382) follow on site: each field loop from instrument to operator screen.
What a FAT typically checks
- Hardware: cabinet build, labelling, power distribution, earthing, redundancy switchover.
- I/O: every channel against the I/O list (often by simulation or with a test box).
- Control functions: control modules, interlocks, sequences step by step, failure reactions.
- HMI: graphics, navigation, faceplates, alarms, trends, user rights, language.
- Communication: fieldbus and network diagnostics, link loss behaviour, time synchronisation.
- Performance: CPU load, scan times, network load, archive capacity.
Making tests useful
- Write test procedures in advance, derived from the functional specification; each step has an expected result.
- Record deviations in a punch list with category (A = must fix before shipment, B = before SAT, C = later).
- Freeze the software version tested; ship exactly that version (checksum or version ID).
- Get signatures from both sides for each completed section.
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Updated 2026-10-04