Patent ID: 7487677

Claim:
A system for determining filter usage comprising: a filtered water container; a hopper fitted to the filtered water container; a filter fitted to the hopper so that water is filtered by draining through the filter into a lower portion of the filtered water container; a sensor positioned so that it is capable of contacting water in the hopper or container, the sensor comprising a first electrode pair and a second electrode pair, each electrode pair comprising a first electrode and a second electrode spaced sufficiently apart from each other so that an electrical property associated with the first and second electrodes can be detected; a detection circuit connected to the first and second electrode pairs in the sensor and capable of generating signals based on the respective electrical property associated with the first and second electrodes in the electrode pairs; and a control unit connected to the detection circuit and capable of receiving signals from the detection circuit, wherein the control unit determines a rate of water level change between the first electrode pair and the second electrode pair and determines, based on the rate of water level change, whether the system is in a functional state in which filter usage is determined or a non-functional state in which filter usage is not determined.