OT: High Frequency Capacitance for level measurement

Hi - off topic but hopefully someone has some experience.
I am looking to install a level detection unit for monitoring fill levels in bottles. The catch is that I need to monitor at a 30mm fill height with a 60mm metal screw cap on the bottle (so the fill height is covered by the screw cap).
We currently use Xray units that detect the level using density. I am needing to repair a unit and have been advised that it is possible to use High Frequency Capacitance to do this. I am having a hard time getting my head around the concept of it working with the metal screw cap covering the product.

Has anyone had experience with this? The unit that I am being offered is made a LogiLevel by Logics & Controls.

Cheers
Peter

Capacitance is a charge between 2 plates. The top plate is floating above the bottle. The bottom plate is the ground plane below the bottle. Think of it as a measurement of the total air volume between the 2 plates. The liquid will take up part of this space. The cap isn't connected to one of the plates, so it will be ignored.

It's more complex than that, especially if the liquid is conductive, but this is an easy way to think of it.

Edit: The liquid must be conductive for this to work. Humidity and temperature are factors, but it looks like they deal with this.

Hi!

Wouldn't weighing be simpler? Or are there speed issues or something?

Thanks Keith- makes sense now.

Boneless - the issue with using weight is speed (450 bph) combined with the variability in glass weight.

Cheers
Peter