| 摘要 |
<p>An intrusion warning system for protecting a wall or fence (1), in particular a chain-link fence (1), against intrusion by cutting through and/or climbing over same. A small- diameter shielded electrical cable (2), e.g. a coaxial cable or a shielded twisted pair is mounted on the fence (1) and the vibrations of the fence detected by sensing the small electrical field generated when the dielectric material between the conductors of the cable (2) is stressed by the minute flexing of the cable (2) causer by such vibrations. The sensed electric field signal is AM derected, shaped and then processed as to duration and persistence. An alarm indicating an attempted cut-through type of intrusion is activated if a preselected number of signals of very short duration, indicating abrupt disturbances of the fence, are detected. A separate alarm indicating an attempted climb-over intrusion is activated only if the detected signal persists for a period of time longer than that of the signals used for the cut-through indication and is present for a predetermined portion of a preset time period.</p> |
