A method and apparatus are provided for monitoring the length of a liquid column such as the filling level of a beverage bottle. A predetermined high frequency signal is applied to a parallel circuit wherein, in one branch, a liquid column is connected by means of electrodes coupled to the ends...http://www.google.com/patents/US4423628?utm_source=gb-gplus-sharePatent US4423628 - Method and apparatus for monitoring the length of a liquid column
