How to fountain soda dispensers work? (The ones that automatically know when to stop.)?

Question

How to fountain soda dispensers work? (The ones that automatically know when to stop no matter how big or small the cup is)

Answer 1

Normally they only have certain size cups that are used even if there are more than one. You hit the correct size and the machine just measures the amount of liquid that comes out and shuts off then. Kind of like how a gas pump measure the liquid coming out and can even be programmed to shut off at a certain dollar amount.

Answer 2

they don't know when to stop...

you choose the cup size...each cup can hold a certain amount of liquid which is already programmed in soda dispenser...that amount comes out with a little left out to allow fizz to go down so wont overflow...after a few seconds lets the rest out