Capacitative proximity sensing system

• Main Authors: WECKENMANN; ALBERT, BRAUTIGAM; ROLF, HAAS; LOTHAR
• Format: Patent
• Language: English
• Published: 05.04.1977
• Subjects: BASIC ELECTRONIC CIRCUITRY; ELECTRICITY; PULSE TECHNIQUE

A leakage field capacitor has two adjacently located surface electrodes placed on an essentially plane support surface. A signal source is connected to one of the electrodes, so that this electrode, which may then be termed the transmitting electrode, will provide an electrical field which is sensed by the other, receiving electrode, which is connected to an evaluation circuit which evaluates disturbance of the field generated by the transmitting electrode. A metallic shield which is electrically floating i.e., is galvanically isolated with respect to the electrodes is connected to the signal source as well as to the evaluation circuit in such a manner as to draw off a portion of the field generated by the transmitting electrode when a mass connected to a terminal of the electrodes - for example ground of chassis - approaches the shield to cause an increase in leakage field being drawn off by the shield and thereby provide a positive signal indication; the grounded mass may, for example, be the finger of a user operating a switch.