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FAT vs SAT in Automation Projects: Key Differences and Best Practices
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Why FAT and SAT Matter
Testing is a critical step in every automation project. To illustrate, Factory Acceptance Tests (FAT) and Site Acceptance Tests (SAT) verify that equipment meets performance, safety, and integration requirements before full-scale production begins. Although often mentioned together, the two stages serve very different purposes. As a result, understanding their distinctions helps ensure smoother commissioning and prevents costly project failures.
What is FAT (Factory Acceptance Test)?
FAT takes place at the supplier’s facility, before equipment is shipped to the customer. Its main purpose is to confirm that machines meet the specifications defined in the URS and FDS. For instance, a packaging line may be tested to demonstrate throughput of 60 units per minute, compliance with ISO safety standards, and proper rejection of defective products. Ultimately, identifying issues during FAT reduces risks during installation and accelerates project delivery.
What is SAT (Site Acceptance Test)?
SAT occurs at the customer’s site after installation. Here, the objective is to validate that the system performs correctly in the real production environment, with all upstream and downstream connections. For example, SAT may confirm that the filler exchanges batch data with the MES in real time, integrates with ERP, and consistently maintains OEE targets. In contrast to FAT, which is supplier-led, SAT requires strong customer involvement to ensure long-term success.
Key Differences Between FAT and SAT
Although both are acceptance tests, their roles differ significantly:
Location: FAT is conducted at the vendor’s facility, while SAT is performed at the customer’s site.
Focus: FAT validates individual equipment against specifications, whereas SAT checks complete system integration.
Timing: FAT occurs before shipment, while SAT follows installation.
Ownership: FAT is largely supplier-driven, but SAT is led by the customer.
Why Both FAT and SAT Are Essential
Some companies try to skip either FAT or SAT to save time, but this often backfires. Consequently, issues overlooked at the supplier’s site may only surface during installation, leading to rework, delays, and cost overruns. Therefore, a well-defined URS should always include acceptance criteria for both stages. By combining FAT and SAT, manufacturers gain confidence in compliance, smooth integration, and predictable ROI.
Best Practices for FAT and SAT
Effective testing depends on strong planning and documentation. First, acceptance criteria for both FAT and SAT should be written directly into the URS. Next, teams must prepare detailed test cases and measurable thresholds. Moreover, cross-functional involvement—from QA to IT to production—is critical for realistic validation. Finally, use the same KPIs across FAT and SAT to ensure consistency in reporting and decision-making.
Sample FAT/SAT Checklist
☐ Functional test cases defined and approved
☐ Compliance standards referenced (OSHA, ISO, CE)
☐ Integration tests included (MES, ERP, conveyors)
☐ Data logging and reporting verified
☐ Operator training observed and documented
Conclusion
FAT and SAT are complementary pillars of automation validation. FAT ensures equipment works as intended before shipment, while SAT confirms integration and performance in the production environment. Together, they minimize risks, reduce costs, and build confidence in automation investments.
FAQ
Q1: Can FAT replace SAT?
No. FAT validates equipment at the vendor site, but only SAT can confirm integration with real factory systems.
Q2: Who is responsible for FAT and SAT?
FAT is supplier-driven with customer oversight, while SAT is customer-driven with supplier support.
Q3: What documents are needed for SAT?
SAT requires the URS, FAT report, integration protocols, and site-specific safety and compliance documentation.
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