Devices for detecting the rupture of an electrical circuit element

Claim 1

Device for detecting the rupture of an electrical circuit element of low resistance, said device comprising means for forming a DC voltage U of which the amplitude varies in the same direction as that developed at each moment at the terminals of the element to be monitored and means for exploiting for signaling purposes or the like the overshoot of a given threshold U o by this voltage U, comprising two electrodes forming a capacitor, of which one is movable with respect to the other between a monitoring position and a warning position, an electret arranged between these two electrodes, whose charge produces a field exerting on said electrodes and electrostatic force H tending to bring them mutually together toward the monitoring position, means for applying between the two electrodes the voltage U in a direction such that the field which results therefrom is opposed to that due to the electret and hence tends to reduce the force H, and means with scarcely reversible action for urging constantly the movable electrode in reverse direction to the force H, the force of these latter means and the charge of the electret being selected so that the overshoots of the threshold U o by the voltage U cause swings of the movable electrode from its monitoring position to its warning position, and the exploiting means being arranged so as to be sensitive to said swings.