Hi,
Colloquially speaking, just check the DCS against your own specifications in FAT and its suitability to your process. Allow the supplier to make amendments and check for them in SAT !
To list a few things, you may check following during FAT
- overall system performance
- system integration
- architecture
- redundancy
- I/O functionality
- Panel Wiring
- Screens
- Diagnosis
- Open/ Close Loop performances
- and so on
You may also ask your supplier as to what they are going to offer in FAT ! (If you don't know, ask them what they can offer without telling them that you don't know it!)
This a function of your control system engineering organization within your company and has to so with a set of standrds and procedures practiced in your company. It has to be developed also jointly with your automation vendor and project engineering group.