Capacitive physical quantity sensor and diagnosis method
First Claim
1. A capacitive sensor for detecting a physical quantity, the sensor comprising:
- a sensor element including a movable electrode displaceable in accordance with a physical quantity, and a fixed electrode faced to the movable electrode, wherein a periodic carrier wave voltage is applied to the fixed electrode; and
a detecting circuit includinga C-V conversion circuit for outputting a voltage signal corresponding to a capacitance between the movable and fixed electrodes, wherein the C-V conversion circuit includes a diagnostic switch,a differential amplification circuit for differentially amplifying the voltage signal from the C-V conversion circuit and outputting the amplified signal as a sensor output in a normal measuring mode, anda high-voltage generating circuit for applying a diagnostic voltage to an input side of the C-V conversion circuit in a diagnostic mode so as to diagnose a sticking of a foreign object between the movable electrode and the fixed electrode, whereinthe periodic carrier wave voltage in the diagnostic mode is larger than the periodic carrier wave voltage in the normal mode,the diagnostic switch is provided between the C-V conversion circuit and the differential amplification circuit, and closed in the normal mode so as to input the voltage signal from the C-V conversion circuit into the differential amplification circuit, andthe diagnostic switch is opened in the diagnostic mode so as to disconnect the C-V conversion circuit and the differential amplification circuit.
1 Assignment
0 Petitions
Accused Products
Abstract
A capacitive sensor for detecting a physical quantity includes a sensor element and a detecting circuit. The sensor element includes a movable electrode and a fixed electrode. A periodic voltage is applied to the fixed electrode. A high-voltage generating circuit applies a diagnostic voltage to an input side of a C-V conversion circuit so as to diagnose a sticking of a foreign object between the movable electrode and the fixed electrode. The C-V conversion circuit includes a diagnostic switch, which is opened in a diagnostic mode. The periodic voltage in the diagnostic mode is larger than the periodic voltage in a normal measuring mode.
-
Citations
8 Claims
-
1. A capacitive sensor for detecting a physical quantity, the sensor comprising:
-
a sensor element including a movable electrode displaceable in accordance with a physical quantity, and a fixed electrode faced to the movable electrode, wherein a periodic carrier wave voltage is applied to the fixed electrode; and a detecting circuit including a C-V conversion circuit for outputting a voltage signal corresponding to a capacitance between the movable and fixed electrodes, wherein the C-V conversion circuit includes a diagnostic switch, a differential amplification circuit for differentially amplifying the voltage signal from the C-V conversion circuit and outputting the amplified signal as a sensor output in a normal measuring mode, and a high-voltage generating circuit for applying a diagnostic voltage to an input side of the C-V conversion circuit in a diagnostic mode so as to diagnose a sticking of a foreign object between the movable electrode and the fixed electrode, wherein the periodic carrier wave voltage in the diagnostic mode is larger than the periodic carrier wave voltage in the normal mode, the diagnostic switch is provided between the C-V conversion circuit and the differential amplification circuit, and closed in the normal mode so as to input the voltage signal from the C-V conversion circuit into the differential amplification circuit, and the diagnostic switch is opened in the diagnostic mode so as to disconnect the C-V conversion circuit and the differential amplification circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7)
-
-
8. A method of diagnosing a physical quantity sensor including a movable electrode and a fixed electrode to which a carrier wave voltage is applied, a conversion circuit for outputting a voltage signal corresponding to a capacitance of the electrodes, and an amplifier circuit for producing a sensor output signal based on the voltage signal, the method comprising:
-
raising the carrier wave voltage at time of diagnosing the electrodes to be higher than that applied normally to detect physical quantity applied to the electrodes; applying a predetermined voltage between the movable electrode and the conversion circuit at time of diagnosing the electrodes; and stopping the voltage signal produced by the conversion circuit from being applied to the amplifier circuit at time of diagnosing the electrodes.
-
Specification