Patent ID: 8040241

Claim:
A capacitance-based occupant detection system comprising: a power supply section for generating an AC voltage; a main electrode provided for a vehicle seat; a main wiring section for connecting the power supply section with the main electrode; a guard electrode provided between a seat frame electrically connected to a vehicle ground and the main electrode, the guard electrode apart from and opposite to the main electrode; an impedance calculation section for calculating a main-body impedance between the main electrode and a vehicle body in an occupant detection mode for ensuring an equal electric potential for the main electrode and the guard electrode and for generating an electric field between the main electrode and the vehicle body electrically connected to the vehicle ground; a Re/Im part calculation section for separating real and the imaginary parts of the main-body impedance based on the main-body impedance calculated by the impedance calculation section; a failure determination section for determining presence or absence of destruction of the main electrode or a short circuit between the main electrode and the guard electrode based on use of the separated imaginary part of the main-body impedance calculated by the Re/Im part calculation section; and an occupant determination section for determining the presence of an occupant on the seat in accordance with a determination result of the failure determination section in the occupant detection mode, wherein the failure determination section determines destruction of the main electrode or a short circuit between the main electrode and the guard electrode, when the separated imaginary part of the main-body impedance calculated by the Re/Im part calculation section in the occupant detection mode is smaller than a predetermined imaginary part threshold value.