MOISTURE-INDEPENDENT CAPACITIVE SENSOR FOR ARBITRARY SWITCHING PROCESSES

• Main Author: Reime, Gerd
• Format: Patent
• Language: English; French; German
• Published: 02.06.2021
• Subjects: BASIC ELECTRONIC CIRCUITRY; ELECTRICITY; PULSE TECHNIQUE

A capacitive proximity sensor comprises a sensor assembly having a resonant circuit which has an inductor (1.3) and a capacitor (1.6), the capacitor (1.6) being formed relative to a ground potential (1.2). The resonant circuit is excited via an exciter circuit (1.1). An output signal (1.8) that can be tapped on the resonant circuit is analysed by means of an analysis circuit (1.9) in order to determine the proximity of an object. A sensor electrode (1.4) is incorporated as resonance capacitor in the resonant circuit. The resonant circuit is excited in a starting state by the exciter circuit (1.1) with a frequency below a resonance frequency of the resonant circuit. A medium (1.7) with a resistive component arrangeable between the sensor electrode (1.4) and the basic potential (1.2) leads to a detuning of the resonant circuit with an output signal (1.8) having an amplitude that is the same or practically the same as in the starting state, whereas the possibility of a further capacitor approaching the sensor electrode (1.4) leads to a detuning of the resonant circuit with an output signal (1.8) having an amplitude that is altered in relation to the starting state, even in the presence of the medium (1.7) having a resistive component. The analysis circuit (1.9) identifies the approach of the further capacitor on the basis of the change to the amplitude of the output signal (1.8). Since the exciter circuit (1.1; 11.6) can be operated such that the resonant circuit is excited periodically with N exciter vibrations, wherein N is a number less than 10, wherein the analysis circuit (1.9) is intended and suitable for analysing, on the resonant circuit, the amplitude of the output signal (1.8; 11.4) during and/or shortly after the N exciter vibrations, a capacitive proximity sensor and a method for determining the proximity of an object to the sensor assembly are provided which do not respond to moderately conductive coverings, such as a closed water film, moist contaminations, a covering of snow or ice, even if these coverings are connected to the electric ground potential and cover the sensor electrode fully or partially. The approach of a hand through these grounded coverings can thus be recognised perfectly.