Intrusion detection system

#This application claims the benefit of U.S. provisional application Ser. No. 60/063,552, filed Oct. 28, 1997, titled INTRUSION DETECTION SYSTEM.

#This invention relates to intrusion detection systems of the type which use taut wires to form a physical barrier, and which use tension sensors coupled to the taut wires to detect attempts to defeat the physical barrier.

#A variety of intrusion detection systems are known, ranging from those protecting private residences to those protecting large-scale, relatively high security, facilities such as airports and military installations. A number of the systems of the second kind, those protecting large-scale facilities, typically provide a combination of a physical barrier and an electronic detection capability. A taut wire intrusion detection system provides such a combination. Such a system is available, for example, from Safeguards Technology of Hackensack, N.J. The present invention provides a solution to a weakness in existing taut wire intrusion detection systems.

#FIG. 1 illustrates one configuration of a typical taut wire intrusion detection system;

#FIG. 2 is a cut-away perspective view that illustrates the details of the connection of the taut wires to a tension-sensing element of FIG. 1;

#FIG. 3 is a block illustration of the components relating to a single wire in one configuration of a taut wire intrusion detection system as illustrated in FIG. 1;

#Some of the past attempts to solve the weakness described above concentrated on improving the tension sensitivity of the systems. These solutions concentrated on the tension sensors and remedying the weakness at its core. Systems were configured such that the sensors will be able to detect a manipulation of the tension and cutting of the wires at a higher degree of sensitivity. One drawback of this approach is the large increase in cost of operation for such systems due to a very high false alarm rate. Another approach provided that the taut wires at the anchor posts be attached to the post not by a permanent fixture, which can be used to clamp a device to and isolate the taut wire from the sensor, but connected to another wire parallel to it as is shown in FIG. 1.

#Referring now to FIG. 1, which illustrates one section of a prior art system, two anchor posts 101 are mounted at opposite ends of the section. A sensor post 103 is mounted at the center of the section between the two anchor posts 101. The sensor post is designed to contain the tension sensors 201 (FIG. 2) that are used to monitor the tensions of the taut wires 104. Such sensor posts and anchor posts are available from Safeguards Technology of Hackensack, N.J. Taut wires 104 are tensioned between the two anchor posts 101. The taut wires 104 are connected to tension sensors 201 (FIG. 2) in the sensor post 103. Slider posts 102, positioned between an anchor post 101 and the sensor post 103, are placed adjacent to the taut wires 104 to provide additional vertical support as to prevent a bowing of the taut wires 104. The slider posts 102 also serve as a mechanism to convert vertical force exerted on the taut wires into horizontal movement. The taut wires 104 are secured to the anchor post 101 by link rods 106. Adjacent taut wires 104 are joined together by link rods 106 that are positioned along the anchor posts 101. Referring to the bottom-most pair 105, for example, the lower taut wire 104 is attached to the bottom end of the lower most link rod 106 on the left-hand anchor post 101A, and the higher taut wire 104 of the pair 105 is attached to the upper end of the same link rod 106. At the opposite, right-hand, anchor post 101B, the higher taut wire 104 of the bottom-most wire pair 105 is paired with the taut wire 104 immediately above it by connecting these wires to the lower and upper portions of a link rod 106, respectively. In this manner, a series of such connections will form a zigzag configuration of taut wire 104 segments and link rods 106 from the bottom to the top of the section. The link rods 106 are not secured to the anchor post, but rather are held in place by the tension the pair of taut wires 105 exert on tabs (not shown) extending from the anchor posts 101. An attempt to cut a single taut wire 104 while maintaining the tension on its sensor post end will cause the link rod 106 to release from the tab and the adjoining taut wire will become slack. The change in tension of the adjoining taut wire 104 will be detected by the sensor attached to it.

#FIG. 2 illustrates the connection of the taut wires to the sensors 201 on the sensor post 103 in the prior art fence section of FIG. 1. The sensor post 103 presented is made of an extruded aluminum rigid channel. The sensors 201 are mounted inside the sensor post 103. Tensioned taut wires 105 are connected to the sensors 201. In the present example a pair of taut wires 105 is attached to each sensor 201 at its top and bottom by a bracket mounted on a metal bolt extending from the sensor 201. The sensors 201 presented are deflection sensors, detecting changes in tension by a deflection of the lower or upper portion of the sensor 201. A deflection of the sensor 201 exceeding a threshold level will cause the sensor 201 to generate an alarm signal. Sensors of this type are available from Safeguards Technology of Hackensack, N.J. Different numbers of taut wires 104 can be attached to each sensor 201 when other kinds of sensors 201 are used. For example, U.S. Pat. No. 4,367,459 (Amir) discloses a sensor that can be attached to more than two taut wires. The present solution (described below) is effective regardless of the number of taut wires attached to each sensor.