CAPACITIES OF APPROACH TO THE EVALUATION OF SMALL CHANGES IN CAPACITY AND THEIR PROCEDURES

摘要

The invention relates to a capacitive proximity switch with an electric bridge circuit for detecting an approaching or remote electro-conductive surface (15) that is part of a capacitor (e.g. C1) of said bridge circuit. At least one capacitor (C1, C2, C3, C4) and optionally at least one resistor (R9, R10) are disposed in branches of the bridge circuit and an alternating voltage is applied to the bridge as a supply voltage (ubr). The proximity switch is comprised of a flat multi-layered plate (10) consisting of at least two electrically insulating layers (13, 14) between which an electro-conductive intermediate layer (11) is provided as the first surface of a capacitor. A flat electro-conductive coating is deposited as a probe (12) on one of the two layers (13, 14), forming the second surface of the capacitor. The electro-conductive surface (15) can move in relation to the probe (12) and forms a second flat, modifiable capacitor therewith, whereby the electro-conductive surface (15) and the probe (12) form one capacitance and the probe (12) and the electro-conductive intermediate layer (11) form another capacitance for one of the two halves of the bridge and the structure thereof represents one half of the bridge. Rectifiers are arranged in the diagonal voltage circuits (DSp1, DSp2) in order to rectify both voltages of the branches of the bridge (uc1, uc3) separately, according to the respective half of said bridge. The diagonal voltage (Ud) of the bridge is only evaluated as a modifying direct current in accordance with the modified capacitance of the modifiable capacitor after both voltages (DSp1, DSp2) of the branches of the bridge have been rectified.