Factory Acceptance Testing: What Manufacturers Should Expect Before a Custom Machine Ships
Elsner Engineering Works | Hanover, PA — Purpose-Built Precision Since 1934
When a manufacturer commissions a custom automated machine, the riskiest moment is not the design or the build—it is the handoff. A machine that arrives on the plant floor and fails to perform stalls production, strands the capital tied up in it, and turns the integrator’s shop into a remote troubleshooting exercise while the line sits idle. Factory Acceptance Testing, or FAT, exists to move that risky moment to the one place where problems are cheap to fix: the builder’s floor, before the machine ever ships. For any company buying custom automation, understanding what a real FAT involves is the difference between a smooth startup and an expensive surprise.
The economic logic behind FAT is well established across engineered systems. A NASA study of error cost escalation through the project life cycle found that the cost to fix an error climbs steeply the later it is discovered, rising by orders of magnitude from early phases to late ones. A problem caught during testing at the builder’s facility is corrected with the machine open, the engineers present, and the production line untouched. The same problem discovered after installation is corrected under production pressure, often with travel, downtime, and lost output stacked on top. FAT is the gate that keeps defects on the cheap side of that curve.
What a Factory Acceptance Test Actually Covers
A FAT is a structured, witnessed test performed at the builder’s facility to verify that a machine meets the agreed specification before shipment. It is not a quick demo. A thorough FAT runs the machine through the full range of conditions it will face in production: every operating mode, every product variant, error states and recovery, and sustained running to confirm the machine holds performance over time rather than just on the first cycle. The buyer typically attends, which turns the FAT into hands-on operator training as well as a verification gate.
The test is measured against criteria defined before the build, not invented on the day. Cycle time, throughput, reject rates, dimensional accuracy, and the behavior of safety and control functions are all checked against the contract specification. Deficiencies are logged on a punch list, resolved, and re-verified. The discipline of testing against pre-agreed numbers is what separates a real acceptance test from a reassuring walkthrough—and it is why the acceptance criteria belong in the purchase agreement from the start.
Why Testing Before Shipment Protects the Project
Verifying a machine before it ships is increasingly treated as core measurement discipline, not a formality. NIST’s work on trustworthy smart-manufacturing systems emphasizes developing and deploying test methods that verify and validate equipment performance and reliability before deployment, precisely because catching reliability problems in a controlled setting prevents downtime once the machine is in production. A FAT is where that principle becomes concrete for a single custom machine.
FAT also protects the relationship between buyer and builder by making “done” objective. When both parties have watched the machine meet its numbers, the handoff is based on evidence rather than optimism. That clarity matters most when a machine has to integrate with existing equipment on arrival, which is its own discipline—covered in [PLACEHOLDER: Brownfield Integration — Making New Automation Talk to Legacy Equipment]. A clean FAT does not eliminate site testing, but it ensures the machine itself is sound before site variables enter the picture.
FAT, SAT, and the Limits of Each
FAT is the first of two acceptance gates. The Factory Acceptance Test proves the machine performs correctly at the builder’s facility; the Site Acceptance Test (SAT) later confirms it performs correctly in the buyer’s actual environment, with real utilities, upstream and downstream equipment, and site-specific conditions that cannot be fully replicated at the builder. Even a flawless FAT does not remove the need for an SAT, because installation quality, power, and integration with the surrounding line are only testable on site.
Understanding this two-gate structure helps manufacturers plan realistically. The FAT de-risks the machine; the SAT de-risks the installation. Both depend on safety functions behaving exactly as specified, which is why machine safeguarding and risk assessment—detailed in [PLACEHOLDER: Machine Safeguarding and Risk Assessment — Designing Automation to OSHA, ANSI/RIA, and ISO 13849]—are verified at FAT rather than discovered at startup. Sequencing testing this way is what lets a complex custom machine move from the builder’s floor to full production without the prolonged, costly shakedown that undermines so many automation projects.
How to Prepare for a Productive FAT
A Factory Acceptance Test returns far more value when the buyer prepares for it rather than treating it as a day to show up and watch. The single most useful preparation is supplying the builder with representative production materials well ahead of the test. A machine that runs the buyer’s actual parts, in the actual range of variation the line will see, is tested against reality; a machine demonstrated on idealized samples can pass a FAT and still struggle in production. Real material, including the difficult and out-of-spec examples, is what makes the test meaningful.
The buyer should also arrive with a clear list of who is verifying what. Operators watch for usability and changeover; maintenance staff probe access for service and the realism of the preventive-maintenance plan; a process engineer checks throughput and quality against the specification. Assigning these roles before the FAT means the limited time in front of the machine is spent deliberately rather than wandering. It also surfaces the practical questions—how a jam is cleared, how a recipe is changed, how an error is acknowledged—while the engineers who built the machine are standing right there to answer them.
Finally, documentation should be reviewed during the FAT, not after delivery. Electrical and mechanical drawings, the control system description, the spare-parts list, and the maintenance procedures are all easier to validate against the physical machine while it is in front of you. Confirming that the documentation matches the as-built machine at the FAT prevents the common frustration of discovering, months later, that a drawing reflects an earlier revision. A machine that arrives with accurate, verified documentation is a machine a maintenance team can actually support.
Elsner Engineering: Custom Automation Built and Tested in Hanover, PA
Elsner Engineering performs rigorous Factory Acceptance Testing on every custom machine before it leaves our 112,000-square-foot Hanover facility, running your production materials and verifying performance against specification—so problems are solved here, not on your floor.
Our Automation Capabilities Include:
- Custom Automation Machinery — Turnkey automated cells and full production lines, designed and built in-house
- Machine Retrofit & Upgrades — Modern controls, vision, and connectivity added to existing equipment
- Contract Engineering — Multi-disciplinary mechanical, electrical, and controls design for complex projects
Planning an automation project? Contact Elsner Engineering to discuss your application with an engineering team that has built machinery in Hanover, PA since 1934.
Frequently Asked Questions
What is the difference between FAT and SAT?
Factory Acceptance Testing (FAT) is performed at the builder’s facility before shipment to verify the machine meets its design specification in a controlled environment. Site Acceptance Testing (SAT) is performed at the buyer’s site after installation to confirm performance under real conditions—actual utilities, integration with surrounding equipment, and site-specific factors. Both gates matter; a successful FAT does not remove the need for an SAT.
Who should attend the Factory Acceptance Test?
The buyer should send the people who will own the machine day to day: a project coordinator, process experts, and ideally the operators and maintenance staff who will run and service it. Attending the FAT verifies performance firsthand and doubles as hands-on training, so the team arrives at startup already familiar with the machine’s operation, changeovers, and error recovery.
What happens if the machine fails part of the FAT?
Deficiencies found during a FAT are expected and are exactly why the test exists. They are logged on a punch list, corrected with the machine accessible and the engineering team present, and then re-verified against the acceptance criteria. Resolving issues at the builder’s facility is far faster and cheaper than discovering them after installation under production pressure.
How do we define FAT acceptance criteria?
The best time to define acceptance criteria is before the purchase contract is signed. The agreement should specify the test items, performance targets (cycle time, throughput, reject rates, accuracy), witness requirements, and responsibility for corrective action. Testing against numbers agreed up front—rather than judged on the day—is what makes a FAT objective and protects both buyer and builder.
Works Cited
Stecklein, Jonette M., et al. “Error Cost Escalation Through the Project Life Cycle.” NASA Technical Reports Server, National Aeronautics and Space Administration, ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100036670.pdf. Accessed 15 June 2026.
“Trustworthy Systems, Components, and Data for Smart Manufacturing Program.” National Institute of Standards and Technology, www.nist.gov/programs-projects/trustworthy-systems-components-and-data-smart-manufacturing-program. Accessed 15 June 2026.