Capacitive device for detecting physical value, has C/V converter that produces output voltage in accordance with change in capacitive element which is defined between movable electrode with integral spring and fixed electrode

摘要

A spring section (22) deforms on influence of a physical value in a certain direction. A movable electrode (24) is formed integral with the spring section and is deformable with the spring section in the deformation direction of the spring section. A fixed electrode (32,42) is arranged opposite to the movable electrode. Periodically changing signals, including a physical value detection signal and a self-diagnosis signal, are selectively sent by a signal feeding unit between the movable and fixed electrodes. A C/V converter produces an output voltage in accordance with a change in a capacitive element which is defined between the movable and fixed electrodes. The capacitance of the capacitive element during sending of the detection signal is changed to allow detection of the physical value. The spring section deforms during sending of the self-diagnosis signal to allow production of a virtual physical value at the movable electrode. The ratio of the frequency of the self-diagnosis signal to the resonance frequency of the spring section is set so that the resonance amplification of the spring section is same or larger than simple on sending of the self-diagnosis signal.