Why Acceptance Tests Get Skipped (And Why That Is Always a Mistake)
Acceptance testing is one of the most commonly abbreviated steps in automation projects. Schedule pressure, budget overruns, and overconfidence in the vendor combine to produce the most expensive phrase in manufacturing: "We will sort it out on-site."
We have seen equipment arrive at customer sites with documentation in the wrong language, safety circuits that had never been tested, and HMI screens still showing the previous customer's product names. All of these would have been caught in a proper FAT.
This guide covers what to actually test, who needs to be in the room, and what happens when something fails.
FAT: Factory Acceptance Test
The FAT happens at the equipment builder's facility, before the machine is shipped. This is your last low-cost opportunity to identify and resolve issues.
Who Should Attend
- Your project engineer or automation lead (mandatory)
- A process engineer who understands the product being manufactured (mandatory)
- Your maintenance lead or electrician (strongly recommended)
- Quality engineering representative (if quality systems are integrated)
Do not send only managers to a FAT. The people who will operate and maintain the equipment need to witness it working — and not working — in a controlled environment.
What to Test at FAT
1. Mechanical build verification
- Compare physical build against approved drawings (mechanical, electrical, pneumatic)
- Check cable routing, connector labeling, and service access
- Verify all safety guarding is in place and interlocked
2. Control system verification
- All I/O points tested (force tested in the PLC, physically verified at the field device)
- Safety circuit testing — E-stops, light curtains, door interlocks, safety relays
- HMI screen navigation, alarm display, and recipe management
3. Cycle demonstration
- Run at target cycle time with production-representative parts
- Demonstrate all product variants if applicable
- Run for a minimum "golden run" duration agreed in the URS (typically 4-8 hours at 95%+ uptime)
4. Documentation review
- As-built electrical and mechanical drawings
- PLC source code backup and version control
- Operations manual and maintenance schedule
- Spare parts list with part numbers
FAT Sign-Off
FAT should result in a signed FAT report with one of three outcomes:
- Pass — equipment ships as-is
- Conditional pass — ships with minor open items tracked on a punch list with committed close dates
- Fail — equipment does not ship until critical items are resolved and re-tested
SAT: Site Acceptance Test
The SAT happens after installation at your facility. By this point, your team has installed the equipment, run utilities (power, pneumatics, network), and completed installation verification.
What Changes at SAT vs FAT
Site conditions introduce variables that the vendor's floor cannot replicate: your actual compressed air quality, your network infrastructure, your ambient temperature, and your material handling interfaces. SAT tests that the system works in your environment.
SAT Test Protocol
1. Installation verification
- All mechanical anchor points, levelness, and alignment
- Electrical installation to your facility panels
- Network and communication to your SCADA/MES
2. Functional re-test
- Repeat critical FAT tests in the production environment
- Verify any items from FAT punch list are closed
3. Interface testing
- Material feeding from upstream (manual or automated)
- Product transfer to downstream
- Data handshake with your MES/ERP if applicable
4. Operator training verification
- Operators demonstrate ability to start/stop, change recipes, acknowledge alarms, and perform daily checks
5. Production run
- Typically 8-72 hours of unattended (or lightly attended) production at full rate and target OEE
Handling Failures at SAT
SAT failures fall into two categories:
- Vendor-scope failures — equipment does not meet the URS specification. The vendor is responsible for resolution at their cost.
- Interface/site failures — your facility did not deliver what was specified (air quality, network bandwidth, feed rate). Responsibility and cost are shared or site-owned.
This is why the User Requirements Specification (URS) and the Interface Control Document need to clearly define what each party is responsible for delivering.
Practical Tips
- Require a FAT plan in the purchase order, not just permission to attend. The vendor should submit a FAT procedure for your approval before the test.
- Bring your own parts to FAT if possible. Vendor-supplied "representative" parts are sometimes not representative.
- Video record the FAT golden run. If an issue appears later, footage is invaluable.
- Do not accept a virtual FAT as a substitute unless there is a genuine force majeure reason. Video calls miss too much.
- Build SAT time into your project schedule. The most common cause of delayed production ramp-up is under-scoped SAT time.
Yudashkin Engineering writes FAT/SAT procedures and attends acceptance tests on behalf of manufacturers globally. Reach out if you need support on your next project.