What is an SAT (Site Acceptance Test)?
An SAT (Site Acceptance Test) is a structured, documented test at the final location in which the customer verifies, after transport and installation, that a machine, installation or control system works as agreed with the real field devices, cabling and interfaces. The SAT follows the FAT (Factory Acceptance Test) at the supplier’s premises. Where the FAT demonstrates with simulated signals that the system meets its specification, the SAT shows that it also works in practice after transport, mounting and connection. A successful SAT is usually the contractual condition for handing the system over to the customer, and often for a payment instalment as well.
🧠 What is tested during an SAT?
The SAT does not repeat the entire FAT. It focuses on everything that could not be tested at the supplier’s factory, or that may have changed during transport and installation:
- Installation check - physical inspection of cabinets, components, labels and power supplies, and verification of earthing, shielding and EMC measures
- Loop check - every signal is traced from the sensor or actuator in the field through the Remote IO and the PLC to the HMI screen, including scaling, units and motor direction of rotation
- Communication - network connections and protocols such as OPC UA, Modbus and ProfiNET, and the behaviour when a connection is lost
- Functional test - start-up, normal operation, shutdown and fault scenarios with the real installation, first without product and then under process conditions
- Safety functions - emergency stop, interlocks, safety PLC and safety relays in their actual wiring
- Integration - interfaces with SCADA, the historian, MES and other higher-level systems
- Performance and redundancy - cycle times, controller and network load, and switchover of redundant components in the final set-up
🔄 How does the SAT relate to the FAT and SIT?
The international standard IEC 62381 describes the test and acceptance phases for automation systems in the process industry. Edition 3.0 was published in July 2024 and added an optional Factory Integration Test (FIT). The standard uses checklists with which the owner, purchaser and supplier agree the test scope and responsibilities in advance.
| Aspect | FAT | SAT | SIT |
|---|---|---|---|
| Location | Supplier’s factory | Customer’s site | Customer’s site |
| Field devices | Simulated | Connected | Connected, under process conditions |
| What is demonstrated | System meets its specification | System works after transport and installation | Interaction with the rest of the plant |
| Test type | Module- and function-oriented | System-oriented, including field wiring | Integration across systems and suppliers |
| Risk to the process | None | Limited, process often not yet running | Real, often during start-up |
In smaller projects the SAT and SIT are often combined. In many projects the SAT is followed by a trial run or performance test, in which the system must run under normal production for an agreed period. The SAT is therefore an important milestone, but not always the very last step before final acceptance.
🔧 How does an SAT work, step by step?
- Write the SAT protocol - the supplier writes test cases that are traceable to the requirements, the functional specification, the I/O list and the drawings. The customer approves the protocol before testing starts.
- Carry over open FAT items - items deferred from the FAT to the SAT are included as separate test cases in the protocol.
- Check the configuration - installed software and firmware versions must match the versions recorded in the FAT report. Every change since the FAT goes through change management.
- Installation and loop checks - mechanical and electrical completion, followed by loop checks per signal. On an operating site this often requires a work permit and agreements with operations.
- Functional and integration tests - run the test cases, record the results and have both parties sign them off.
- Punch list and retest - deviations go onto a punch list, categorised as blocking handover, to be resolved within an agreed period, or administrative.
- SAT report and handover - after approval come the SAT report, the final as-built documentation and the formal handover to the operations organisation.
| Test item | Typical evidence in the SAT report |
|---|---|
| Installation | Signed inspection checklist, earthing and insulation measurement report |
| Loop checks | List per signal with date, tester and result |
| Functional test | Signed test cases referencing the specification |
| Safety functions | Test record per safety function, including response times |
| Cybersecurity | Checklist for access, hardening, backup and restore |
| Configuration | Software and firmware versions, checksums or project version |
🏭 Where is an SAT used?
An SAT is part of almost every project in which a control system is delivered on site:
- New installations and lines - from OEM machines and turnkey projects to complete process plants with a DCS
- Upgrades and migrations - replacement of controllers, drives or SCADA systems in a running plant
- Network integration - commissioning of OT networks with firewalls, routers and switches
- Sectors - water treatment, food and beverage, chemicals, pharma, power plants and discrete manufacturing
In the pharmaceutical industry, EU GMP Annex 15 (in force since October 2015) describes the FAT and SAT as part of qualification. Tests from the FAT need not be repeated on site if it can be shown that transport and installation do not affect the functionality. The SAT often ties in with installation qualification (IQ) and operational qualification (OQ). GAMP 5 Second Edition from 2022 encourages the reuse of well-documented supplier tests.
For safety-related systems, IEC 61511 requires on-site validation of the SIS, in which every safety function is tested with the real sensors and final elements. In practice this validation is often a separate part of, or runs alongside, the SAT. For machinery, CE marking remains a separate obligation of the manufacturer: under the Machinery Directive and, from 20 January 2027, under the Machinery Regulation.
🔐 How do you test cybersecurity during the SAT?
The SAT is the moment the system sits in your real network for the first time. Cybersecurity therefore belongs in the SAT protocol rather than in a separate review afterwards:
- Access - verification of user access control, password policy and RBAC, and removal of default and test accounts used during commissioning
- Network - Firewall rules and network segmentation as designed, and temporary connections such as modems or supplier VPN access disabled
- Encryption - secure communication, for example via TLS for OPC UA or management interfaces
- Hardening - unused ports, services and USB access disabled according to the hardening plan
- Logging - logging functions and an audit trail that record login attempts and changes
- Recovery - a current backup of controllers and servers, a tested restore and documented recovery procedures
- Documentation - an updated asset inventory with firmware and software versions
Ask the supplier to demonstrate how it meets IEC 62443-2-4, the standard with requirements for service providers that integrate and maintain systems. For organisations covered by NIS2, which the Netherlands implemented through the Cyberbeveiligingswet in force since 15 August 2026, a documented security SAT helps demonstrate supply chain security. This is how Security by Design principles are tested before go-live.
❓ Frequently asked questions
Is an SAT mandatory?
An SAT is usually not a legal obligation but a contractual agreement between customer and supplier. In regulated sectors such as pharma, acceptance on site is in practice a standard part of qualification. For safety instrumented systems under IEC 61511, on-site validation is required.
Who carries out the SAT?
The supplier or system integrator carries out the SAT and provides the test procedures and the people. The customer attends as a witness and signs off the results, often together with operations, maintenance and the person responsible for OT security.
How long does an SAT take?
The duration of an SAT depends on its scope: a single machine is often tested in one to a few days, while a large process plant with thousands of signals can take weeks. The number of loop checks and the availability of the process usually determine the lead time.
Can the SAT be skipped after a good FAT?
An SAT can be shortened after a good FAT, but rarely skipped altogether. Field wiring, earthing, transport damage and real process conditions are only covered on site. Tests that are demonstrably unaffected by transport and installation can, however, be reused from the FAT.
What happens if the SAT fails?
When an SAT fails, the findings go onto a punch list and the supplier resolves them. Blocking items are retested before handover takes place. Minor items can be accepted with an agreed deadline for resolution.
What is the difference between an SAT and an SIT?
The SAT demonstrates that one system works as specified after installation on site. The SIT (Site Integration Test) demonstrates that this system works together with the rest of the plant and with systems from other suppliers.
📌 In summary
An SAT confirms at the final location that a machine or control system works with the real field devices and interfaces after transport and installation. Installation, loop checks, functions, safety functions, integration and cybersecurity are tested against a protocol approved in advance. IEC 62381 provides the structure for FAT, SAT and SIT, and a strict punch list and version control make the difference.
The SAT is the final piece of engineering, installation and security: the formal moment to ensure that the system does what was agreed in the real production environment, before handover to operations.