Patent ID: 7168320

Claim:
A method of sensing physical quantity using a capacitive sensor equipped with a first fixed electrode and a second fixed electrode disposed face to face and a movable electrode disposed between the first and second fixed electrodes so as to form variable first and second capacitors whose capacitances vary in response to the physical quantity sensed by the movable electrode, comprising: first adjusting a first bias voltage applied between the first fixed electrode and the movable electrode and a second voltage applied between the movable electrode and the second fixed electrode respectively to allow the movable electrode to be brought into contact with either of the first and second fixed electrodes; second adjusting the first and second bias voltages to allow the movable electrode to return to a non-contact original position thereof between the first and second fixed electrodes, the second bias voltage adjustment performed by the second adjusting means following the first bias voltage adjustment performed by the first adjusting means; and detecting, for self-diagnosis of the unit, an output signal corresponding to a relationship of capacitances between the first and second capacitors.