Abstract: A capacitance intrusion detection system for use with a metal object or objects insulated from ground comprises a circuit for cyclically charging and discharging the object at a relatively low frequency, for example, less than 500 Hz, and simultaneously integrating the charge on the object to develop a DC voltage proportional to the capacitance of the object. The integrating network is AC coupled to a bandpass filter which passes signals having frequencies corresponding to changes in capacitance of the object caused by an intruder and these signals are applied to a threshold circuit for activating an alarm when an intrusion occurs. Tamper alarm circuits are provided to detect unauthorized disconnection of any portion of the protected object (decrease capacitance) or the addition of capacitance in an attempt to defeat the system.

Abstract: An improved low-cost line transducer comprises a pair of electret covered conductors twisted about each other to form longitudinal helices and mechanically coupled to a medium that transmits mechanical forces transversely of the conductors. A change in the conductor-electret spacing caused by the mechanical disturbance generates an electrical signal between the conductors which is detected and processed by appropriate circuitry for indicating the occurrence of the disturbance. This simplified line transducer has improved sensitivity to the low frequency disturbances because of the non-symmetrical relation of the two conductors throughout their length. Undesired hum and noise picked up by the unshielded line is reduced or eliminated by appropriate circuits in the signal processor.

Abstract: An adaptive gain control for a signal processor of an intrusion detection system comprises a circuit which utilizes the weighted summation of selected characteristics of sensed signals for producing optimum control of the gain of the circuit for discriminating between target and non-target signals more effectively. The parameters of signal envelope, envelope amplitude variance and signal frequency obtained from a processor such as that described in U.S. Pat. No. 3,696,369 are fed to a summing amplifier through resistors having weighted values calculated from previously recorded seismic signals obtained from several previously identified sites which, taken as a group, are representative of the type or types of sites in which the detection system is to be installed.

Abstract: This fence protection system comprises an elongated electret cable for sensing vibrations on a fence and an electronic processing circuit connected to the cable for discriminating against spurious signals such as those caused by raindrops on the fence and nuisance signals produced by stick dragging on the fence. This circuit comprises a charge amplifier connected directly to the cable transducer and series connected burst width and interburst discriminators in conjunction with parallel connected pulse counter and integrator means feeding an alarm mechanism through an OR gate; signals produced by an intruder climbing or cutting the fence are distinguished from spurious raindrop and stick dragging signals and produce and alarm.