There are several ways to achieve reliable filament diameter, and I named quite a few.
If you are looking for a way to set your machine and walk away (not always recommended) and come back to a perfect spool, I outlined several points.
Your last sentence sounds like you are having problems. Give us more information, and we can help walk you through your current setup. If you are just experiencing diameter inconsistencies, again, I asked a few question to help diagnose.
Are you looking for an automated design that pulls the filament as it drops to maintain a consistent diameter? Or just something that checks it with an autostop?
Printit Mason and Printit Horizon printers
Multiple SD2s- Bulldog XL, E3D v5/v6/Lite6, Volcano, Hobb Goblin, Titan, .9 motor, Lawsy carriages, direct Y drive, fishing line...the list goes on
Filawinder and Filastruder #1870.....worth every penny!