Method and device for capacitive detection of objects

G - Physics – 01 – V

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G01V 3/08 (2006.01) A61B 5/00 (2006.01) G08B 13/26 (2006.01)

Patent

CA 2693626

Proximity of a person (BOD1) causes a change in the capacitance value of a sensor capacitor (CX) having a pair of capacitive plates (10a, 10b). Said change is detected by: - charging said sensor capacitor (CX) by coupling it to a voltage supply (40), wherein said voltage supply (40) is disconnected from a tank capacitor (C2) during said charging, - transferring charge from said sensor capacitor (CX) to a tank capacitor (C2), wherein said voltage supply (40) is disconnected from said tank capacitor (C2) during said charge transfer, - repeating said charging and charge transfer several times, - monitoring the voltage (VX) of said tank capacitor (C2), and -- determining at least one value which depends on the rate of change of the voltage (VX) of said tank capacitor (C2). The capacitance of the capacitive sensor is typically low, typically in the order of 100 pF to 1 nF. The capacitance of the tank capacitor (C2) may be several orders of magnitude higher than the capacitance of the sensor capacitor (CX). The large tank capacitor (C2) acts as a part of a low-pass filter which effectively filters out signal noise.

La proximité d'une personne (BOD1) provoque un changement de la valeur de capacité d'un condensateur de détecteur (CX) ayant une paire de plaques capacitives (10a, 10b). Ledit changement est détecté par : - la charge dudit condensateur de détecteur (CX) par son couplage à une source de tension (40), ladite source de tension (40) étant déconnectée d'un condensateur réservoir (C2) pendant ladite charge, - le transfert de la charge dudit condensateur de détecteur (CX) à un condensateur réservoir (C2), ladite source de tension (40) étant déconnectée dudit condensateur réservoir (C2) pendant ledit transfert de charge, - la répétition plusieurs fois de ladite charge et dudit transfert de charge, - la surveillance de la tension (VX) dudit condensateur réservoir (C2), et - la détermination d'au moins une valeur qui dépend de la vitesse de changement de la tension (VX) dudit condensateur réservoir (C2). La capacité du détecteur capacitive est typiquement faible, typiquement de l'ordre de 10 pF à 1 nF. La capacité du condensateur réservoir (C2) peut être de plusieurs ordres de grandeur supérieure à la capacité du condensateur de détecteur (CX). Le grand condensateur réservoir (C2) sert de partie d'un filtre passe-bas qui filtre efficacement un bruit de signal.

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