Tilt sensor

A tilt sensor comprising:

• a printed circuit board disposed in a direction normal to a reference plane for measuring a tilt angle;
• a pair of differential electrodes mounted on the printed circuit board, said differential electrodes are electrically independent of each other;
• a common electrode plate opposed to the pair of differential electrodes with a predetermined gap therebetween;
• a common electrode fixed to the printed circuit board by a terminal formed from the common electrode plate;
• an oil case for storing the pair of differential electrodes and the common electrode plate in a closed space formed by said oil case and the printed circuit board;
• a dielectric liquid filled into the closed space in a state where a dielectric liquid surface level varies according to the tilt angle of the reference plane;
• and
• a signal processing circuit section which is formed on the printed circuit board and is capable of producing the output signal of the level corresponding to the difference in capacity between two capacitors, each of said two capacitors includes the common electrode and an electrode from the pair of the differential electrodes, as a tilt detection output,
• wherein the pair of differential electrodes are mounted electrically independently of each other in the regions which are divided by a first intersection where a plane parallel to the reference plane intersects the printed circuit board, and are formed in a shape symmetric with respect to the first intersection and each of the pair of differential electrodes is formed in a shape symmetric with respect to a second intersection where a plane normal to the reference plane intersects the printed circuit board;
• wherein the dielectric liquid is filled into the closed space to the level of the first intersection;
• and
• wherein the signal processing circuit section comprises:
• a buffer circuit for receiving a signal of a predetermined frequency from the outside and supplying it to the common electrode;
• a first capacity-voltage conversion circuit for rectifying a signal taken out of a first capacitor constituted by the common electrode and one electrode of the pair of differential electrodes and converting it into voltage;
• a second capacity-voltage conversion circuit for rectifying a signal taken out of a second capacitor constituted by the common electrode and the other electrode of the pair of differential electrodes and converting it into voltage;
• and
• a differential amplifier circuit for producing a difference voltage output between the output voltage of the first capacity-voltage conversion circuit and that of the second capacity-voltage conversion circuit.