Patent ID: 7575085

Claim:
A capacitance-based sensor that is arranged in a seat of a vehicle and senses presence of an occupant in the seat, the capacitance-based sensor comprising: an occupant sensing electrode that is embedded in the seat; an empty seat capacitance reducing electrode that is placed between the occupant sensing electrode and a seat frame of the seat, which is connected to a vehicle ground, wherein the occupant sensing electrode is connected to the vehicle ground, and the empty seat capacitance reducing electrode is connected to an intersecting point which connects between the occupant sensing electrode and the vehicle ground; an electric current sensing device that measures an electric current and is inserted in one of a first location, which connects between the occupant sensing electrode and the intersecting point, and a second location, which connects between the vehicle ground and the intersecting point; and a drive device that generates a drive voltage and is inserted in the other one of the first location and the second location, wherein the empty seat capacitance reducing electrode is connected to the intersecting point to reduce a capacitance that is measured with the electrical current sensing device in an empty state of the seat where the occupant is not present on the seat; wherein in an occupant sensing operational mode of the capacitance-based sensor for sensing the occupant on the seat, the drive device applies a voltage between the occupant sensing electrode and the vehicle ground, and the electric current sensing device measures an electric current between the occupant sensing electrode and the vehicle ground; in a malfunction sensing operational mode of the capacitance-based sensor for sensing a malfunction of the capacitance-based sensor, the drive device applies a voltage between the occupant sensing electrode and the empty seat capacitance reducing electrode, and the electric current sensing device measures an electric current between the occupant sensing electrode and the empty seat capacitance reducing electrode; in the occupant sensing operational mode of the capacitance-based sensor, the drive device and the electric current sensing device are connected in series between the occupant sensing electrode and the vehicle ground in this order, and the empty seat capacitance reducing electrode has the same electric potential as that of the vehicle ground; and in the malfunction sensing operational mode of the capacitance-based sensor, the drive device and the electric current sensing device are connected in series between the occupant sensing electrode and the empty seat capacitance reducing electrode in this order.