Who this is for: businesses purchasing or upgrading control and automation systems.
FAT and SAT are verification stages to define within an automation project. A Factory Acceptance Test normally takes place at the supplier’s premises or in a prepared environment before delivery. A Site Acceptance Test checks the installed system in the customer’s environment. Their actual scope depends on the contract, process and tests that can be performed.
A demonstration in which the cycle works once is not an acceptance plan. Deciding whether a delivery is ready requires each requirement to be connected to a test, an expected result and a person able to assess it. This preparation starts before the software and control cabinet are finished.
Separate pre-delivery and on-site verification
FAT can check logic, sequences, interfaces and simulated exchanges, with simulation clearly identified. SAT checks the agreed requirements on the installed system using the real interfaces specified for the test. Passing a simulated test does not automatically cover every condition at the installation site.
Prepare two connected lists: tests possible before delivery and checks deferred until installation. Record the reason for each deferral and the resources required. This prevents a requirement from disappearing simply because it could not be verified in the first session.
For the process industries, ISA distinguishes the FAT/SAT scope from loop checks, commissioning and MES testing. Identify any such activities separately, with prerequisites and responsible people. SAT should not become a catch-all label for every task that needs to take place on site.
References: Siemens — Commissioning and virtual simulation · ISA — ISA-105: acceptance testing and commissioning scope
Write a repeatable test record
A test record identifies a recognisable starting configuration, the actions to perform and the expected result. If an order can be submitted twice, for example, verify that duplicate handling matches the specification. Recording only ‘test completed’ does not explain what was actually observed.
Scroll horizontally to see every column.
| Field | Information to agree |
|---|---|
| Requirement | Identifier and expected behaviour from the specification |
| Prerequisites | Software version, configuration, data and tools |
| Procedure | Actions, sequence and verification conditions |
| Outcome | Observed result, supporting evidence and deviations |
| Responsibility | Tester, assessor and next action |
Include interrupted operation and invalid data
A system needs defined behaviour when information is missing, a connection fails or a sequence cannot continue. Agree which conditions to represent and how to do so safely. Do not improvise failures on a production line to complete a checklist.
Tests may cover communication loss and recovery, permissions, invalid recipes and restart after an interruption. Functional safety verification requires specific competence and procedures: a routine software FAT does not replace that work or amount to certification.
- State the expected response before introducing a fault condition.
- Record the version and configuration used for the test.
- Keep evidence of recovery, not only the error message.
Manage defects, retests and handover
Give each defect a description, impact, owner and closure condition. Agree which problems prevent acceptance and which may remain open with an agreed action and deadline. This classification should be agreed in advance, rather than imposed at the end of the test session.
Following a correction, repeat the affected test and assess related functions that may have changed. Handover includes the records, final versions, usable recovery copies, instructions and outstanding actions. Acceptance should refer to this specific set of evidence.
Acceptance preparation checklist
- Approved specification with requirements linked to tests.
- Clear distinction between real signals, simulations and site checks.
- Agreed versions, personnel, tools and starting conditions.
- Pass criteria and defect classifications defined before the session.
- List of final documents and responsibility for closing open actions.
Common questions
Does every project need both FAT and SAT?
The route depends on the project and contractual arrangements. The distinction remains useful for small interventions: separate what can be demonstrated before installation from what requires the actual plant.
Does an acceptance report replace conformity documentation?
No. It records agreed checks and their outcomes. Compliance obligations and specialist verification have their own scope and need to be identified separately for the system concerned.
Sources and further reading
Apply this to your project.
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