I have been asked by a client which is a beer producer to check if plastic boxes that are running on a conveyor belt have been filled with beer bottles. The bottles in the plastic box are approximately 25mm lower than the top of the box. One solution I have thought of is to use inductive proximity sensors installed above the box and sense the metal cap of the bottles which are four in a raw. I have seen some sensors which can sense up to 40mm but am not sure if these could be reliable for my application. I would like also to know if it’s a good idea to have proximity sensors installed so close to each other as the bottle caps are approximately 65mm apart (center to center of caps). Please take into consideration the small size of the cap and also that when moving on the conveyor belt bottles are shaking little so the target is not so stable or big!