Proximity detector between a metallic mass and an element to which is applied an electric voltage

Claim 1

In a proximity detector for detecting the proximity of a metallic mass to a live element including an electric circuit for feeding a safety device such as the control coil of a circuit breaker, the power supply switch of a motor controlling displacement of the mass, an alarm, an emergency ground and the like, the improvement wherein said circuit includes (a) a DC power supply source (6); (b) first sensing means (5) for producing a first electrostatic potential upon direct contact of the mass with the live element; (c) second sensing means (2) for producing a second electrostatic potential when the mass is in close proximity to the live element; (d) field effect transistor means (8, 8') for detecting the first and second electrostatic potentials, said field effect transistor means including plural gate means each connected with a terminal of said first and second sensing means respectively and with a pole of said DC power supply source, said field effect transistor means also including a sourcedrain circuit polarized by said DC power supply source; (e) a resistive element (7) connected between said pole and said terminal of said first sensing means; and (f) a capacitive element (18) connected between said pole and said terminal of said second sensing means, whereby when at least one of said first and second potentials is altered, the conductibility of said field effect transistor means is modified to produce an output to the safety device.