IE45206B1 - Fence - Google Patents

Abstract

The wire comprises a central conductor (1) jacketed by a thin insulating sheath (2) and surrounded by conductors (3). The conductor (1) and one of the conductors (3) are connected to a resistance bridge, the diagonal of which is connected to an amplifier controlling an acoustic alarm. Any pressure on the wire (wire-cutter, weight of a person trying to scale the fence, etc.) moves the wire (3) closer to the wire (1) and causes the contact resistance between these two wires or the capacitance to vary, which destroys the balance of the bridge and triggers the acoustic alarm.

Description

The invention relates to a fence, fence and wall panels and fencing mesh incorporating a plurality of elongate flexible electrically conductive members.

Tt is a known practice to make fences by means of 5 wires, particularly composite wires. However, such known fences are not entirely secures it is possible to break through or climb them without being detected, particularly as the fences are often set up around very extensive grounds so that permanent guard surveillance of the whole fence is nearly impracticable.

It is an object of the invention to provide such a fence, with improved reliability of detection.

According to one aspect of the present invention there is provided a fence including one or more elongate flexible elements each o£ which comprises a plurality of electrically conductive members at least some of which are twisted into a strand, a continuous envelope of insulating material surrounding at least one of the electrically conductive members, the envelope of insul’ 20 ating material being sufficiently thin that when the said members are moved laterally relative to one another a change occurs in the resistance and/or capacitance therebetween.

Any attempt to cross the fence will inevitably 25 go together with the exertion of pressure on the elongate flexible member(s) of the frame and will thus be detected. The application of the invention thus allows 40206 the making of fences of any desired type, which are considerably more secure than the known fences.

In another aspect the invention provides a prefabricated fence panel comprising an open frame across which extend one or more elongate flexible elements each comprising a plurality of electrically conductive members at least some of which are twisted into a strand, a continuous envelope of insulating material surrounding at least one of the electrically conductive members, the envelope of ins-.lating material being sufficiently thin that when the said members are moved laterally relative to one another a change occurs in the resistance and/or capacitance therebetween.

In a further aspect of the invention/there is provided a mesh for the construction of fencing comprising one or more elongate flexible elements each of which comprises a plurality of electrically conductive members at least some of which are twisted into a strand, a continuous envelope of insulating material surrounding at least one of the electrically conductive members, the envelope of insulating material being sufficiently thin that when the said members are moved laterally relative to one another a change occurs in the resistance and/or capacitance therebetween.

The or each element may comprise a first central filamentary conductor enveloped in a thin layer of insulation material and a number of second conductors wound around the first.

Alternatively, the element(s) may comprise a number of conductive members twisted into a strand, of which at least one is separated from the others by an insulating layer. ιθ 6 - 4 Preferably, the composition and thickness of the insulation material are such that when a pressure is applied on the conductor, there mainly is a change in resistance between the conductors. Polytetrafluoro5 ethylene is found to be a suitable material.

Pences according to the invention may suitably be used with a circuit connected xvith both members for detecting a deviation in the nominal value of the resistance and/or the capacity between them, and an alarm circuit controlled by this circuit.

A fence of the type whereby any movement of the threadformed fence elements is detected by movementsensing detectors is known. One such detector in the form of a switch is described in U.S. Patent No.

IS 3,534,638.

Although such a fence generally offers good protection, in principle it is possible to break through the fence by clamping some of the wires to two posts located between the movement-sensing switches and subsequently cutting said wires between said posts.

Since the wires are clamped to the posts at both sides of the place of cutting, the switches will not react to this cutting and tha action of breaking through the fence will not be detected. Xt is one aim of the present invention to obviate this disadvantage and to provide a fence of the aforesaid type, whereby action on the wire itself is detected, so that the fence is substantially more secure.

In a yet further aspect of the present invention there is provided a wall panel of solid material in xvhich is embedded at least one elongate flexible element comprising a plurality of electrically conductive <*s2 06 members at least aome of which are twisted into a strand, a continuous envelope of insulating material surrounding at least one of the electrically conductive members, the envelope of insulating material being sufficiently thin than when the said members are moved laterally relative to one another a change occurs in the resistance and/or capacitance therebetween.

Some embodiments of the invention will now be described, by way of example only, with reference to the accompanying dra/ings, in which:Figure 1 is a perspective view of one type of elongate flexible element for use in the invention? Figure 2 is a block diagram of an alarm circuit for use with fences according to the invention; Figure 3 is a perspective view of a fence according to the invention; Figure 4 is a front view of a prefabricated fence panel according to the invention; Figure 5 is a view showing mesh according to the invention; Figure 6 is a perspective view of a wall panel according to the invention.

Figure 1 shows a flexible elongate element or wire. It comprises a central conductor 1 located in an insulating sleeve 2 (e.g. of p.t.f.e.), the whole being enveloped by strands or conductors 3. It is also possible to make the wire in the manner shown in Figure 1, omitting the central conductor 1 and the insulating sleeve 2 and enveloping one of the filaments of the strands 3 in a thin insulating layer.

When applying a pressure on the strands 3, the insulating layer 2 is modified in such a way that the contact resistance between the conductor 1 and the strands 3 is noticeably reduced. This can be detected by a suitable detector circuit.

The wire of Figure 1 can be made on existing simple cabling machines, the core conductor 1 with the insulating layer 2 being placed on the spool which normally carries the central strand, whereas the other strands 3 are placed on the other spools of the cabling machine.

Figure 2 shows c block diagram of an alarm circuit which may be connected to a fence according to the invention and employing the wire of Figure 1. It comprises a resistance bridge fed by a battery 14, with fixed resistors 15 and 15 and an adjustable resistor 17. The outputs 18, 19 are connected to an amplifier 20 to whose output a klaxon 21 is connected. The central conductors of the wires are connected to lead 22 and the outer conductors of the wires to lead 23. formally, this means that when no pressure is applied to the wires (the bridge having been balanced by means of the resistor 17) there is no output signal .between, tne leads 18 and 19. VJhen pressure is applied on one of the wires of the fencing installation, the resistance between the leads 22 and 23 decreases so disturbing the bridge balance and causing a potential difference between the leads 18 and 19· This is amplified by the amplifies 20 and actuates 'the alarm klaxon 21.

Figure 3 shows a fence 27 according to the invention comprising a number of posts 23 between which are tensioned wires 29, of the type described above, which are connected to the alarm circuit of figure 2. The wires are connected to movement-sensitive switches 30 provided on a number of regularly spaced posts for example posts 28a. and 28b. - 7 These switches are known (e.g. U.S. Patent No. 3,634,638) and do not react to slow changes to the positions of the wires connected to them (evidently within certain limits), but they do react to swift changes. Variations in fence temperatures do not affect the installation. However, the weight of a person intending to climb the fence or the weight of an object placed against it do activate the switches 30.

It is imaginable that such a fence may be crossed by clamping the r-’iras to the posts 2Sc., 28d located between the posts 28a, 28b which are provided with switches, by means of a suitable clamp, and subsequently cutting the wires between the posts 28c. and 28d, say on the spot indicated by the chain lines 31.

By using wires of the type described this problem may be avoided and any action on the fence can be immediately detected by the alarm circuit.

Figure 4 is a front view of a prefabricated fence panel 32, comprising a frame having long sides 33a, 33b and short sides 34 a, 34b. Across frame 32 extends, in the form of a mesh, a wire 35 of the type shown in figure 1. The wire starts in the left top corner 36 and leaves the panel in the right bottom corner 37.

As the figure shows the wire is incorporated in the frame 32 in the form of a mesh. Figure 5 is a larger scale view of the mesh formation. It is possible to form the meshes by twisting the wires, as designated by reference numeral 38, about each other, or by using connecting sleeves 39 which form the corners of the meshes.

It is clear that a fence comprising a number of the above-described panels containing wires that are Δ S3 Ο δ - δ connected to a detection circuit of the kind described in.Figure 2, may be made in a fast and'inexpensive way, while offering improved security.

It is also possible to embed wire of the type described above, either in a mesh configuration or in another configuration, into a solid material such as a synthetic material or concrete. Figure 6 illustrates this possibility. The figure shows a mesh 40 of the type illustrated in Sivure 5 embedded in the slab 41, which, as noted above may be made of concrete or suitable synthetic material. The figure is a partly eufc-away elevation of the slab 41 revealing the mesh configuration. The input end of the wire is at point 42, the output end at point 43. A number of theca elensenus may also in this case be connected in series or in parallel.

Such an embodiment is particularly suited to be partially buried and to provide in this way an aboveground fence with an impenetrable extension underground.

It will be appreciated that, if desired, the fence, panel or mesh may also include wires of conventional construction in addition to the elements having members separated by insulating material.

Claims (15)

1. A fence including one or more elongate flexible elements each of which comprises a plurality of electrically conductive members at least some of which are twisted into a strand, a continuous envelope of insulating material surrounding at least one of the electrically conductive members, the envelope of insulating material being sufficiently thin that, when the said members are moved laterally relative to one another, a change occurs in the resistance and/or capacitance therebetween.

2. . A fence according to Claim 1 in combination with apparatus adapted to provide an alarm signal in response to variation of the resistance or capacitance between said members. ι

3. A fence according to Claim 1 or 2 in which a plurality of said elements extend under tension between : supporting posts.

4. A fence according to Claim 3, in which the ί elements are connected to movement-sensing detectors.

5. A prefabricated fence panel comprising an open frame across which extend one or more elongate flexible elements each comprising a plurality of electrically conductive members at least some of which are twisted into a strand, a continuous envelope of insulating material surrounding at least one of the electrically conductive members, the envelope of insulating material being sufficiently thin that when the said members are moved laterally relative to one another a change occurs in the resistance and/or capacitance therebetween.

6. A mesh for the construction of fencing comprising one or more elongate flexible elements each of which comprises a plurality of electrically conductive members at least some of which are twisted into a strand, a continuous envelope of insulating material surrounding at least one of the electrically conductive members, the envelope of insulating material being sufficiently thin 5 that when the said members are moved laterally relative to one another a change occurs in the resistance and/or capacitance therebetween.

7. A wall panel of solid material in which is embedded at least one elongate flexible element comprising 10 a plurality of electrically conductive members at least some of which are twisted into a strand, a continuous envelope of insulating material, surrounding at least one of the electrically conductive members, the envelope of insulating material being sufficiently thin that when the 15 said members are moved laterally relative to one .another a change occurs in the resistance and/or capacitance therebetween.

8. A wall panel according to Claim 7 in which the solid material is concrete. 20

9. An apparatus according to any one of Claims 1 to 5 or Claim 7 or 8 wherein the element(s) are in the form of a mesh.

10. An apparatus according to any one of Claims 1 to 9 in which the or each element comprises a first 25 central filamentary conductor enveloped in a thin layer of insulating material and a number of second conductors wound around the first.

11. An apparatus according to any one of the preceding claims, the or each element having only a single 30 layer of insulating material between its members.

12. An apparatus according to Claim 11 in which the thickness of said layer is substantially 0.35 mm.

13. An apparatus according to any one of the preceding claims, in which the insulating material is polytetrafluoroethylene.

14. An apparatus according to any one of the 5 preceding claims, including further flexible elongate elements which do not comprise members insulated from one another.

15. Pences, panels or meshes substantially as herein described with reference to the accompanying 10 drawings.