GB2311156A - Alarmed wire mesh fencing - Google Patents

Abstract

A fence consisting of plastic-coated wire which has been woven to form a mesh. The mesh is attached to posts 1 and a selected number of the strands forming the mesh are electrically connected in series by the use of terminal strips 2 to form a continuous loop 3. The loop is taken by cable 4 to a suitable electronic alarm which is designed to be activated is the loop is severed. The fence includes provision for a combined closed/open circuit loop (Fig 2) and anti-climbing features (Figs 3, 4, 5 and 6).

Description

IMPROVEMENT TO WIRE MESH FENCING This invention relates to an improvement in wire mesh fencing.

A plastic-coated wire mesh fence consists of strands of tough plastic coated wire which, during manufacture, are formed into a strong mesh network in any one of a number of configurations or patterns. The mesh is fastened to fence posts to form a fence which is relatively inexpensive and long lasting. However, it provides poor security since it is a fairly simple matter for an intruder to cut a hole in the mesh large enough to permit passage through the fence.

An improvement to the security afforded by such a fence could be made by taking advantage of the fence's construction; since the strands of the wire mesh are essentially electrically insulated wires, these could be made to form the closed-circuit detector loop of an associated intruder alarm, using established electronic technology, such that if any one of the conducting strands were to be cut then the electronic intruder alarm would be activated.

By incorporating three electrical conductors in the strands which form the detector loop, then combined closed-circuit and open circuit detectors could be employed, if desired.

This invention encompasses those plastic coated wire mesh fences which employ plasticinsulated mesh strands which are horizontally aligned relative to the ground.

According to the present invention, during the manufacture of the wire mesh a number of the horizontally aligned strands are substituted by electrically conducting strands of copper or other metal of a suitably high electrical conductivity; these are plastic-coated in a similar manner to the conventional strands of the mesh such that their physical dimensions and appearance are indistinguishable from the conventional strands. The number and positioning of the electrically conducting strands are such that any attempt to cut a hole large enough to permit bodily passage through the fence would not be possible without severing one or more of the conducting strands.

These electrically conducting strands may then be made to form a closed-circuit detector loop running throughout the length of the fence.

Terminal strips are provided in hollow terminal posts for the purpose of interconnecting the strands which form the detector loop. The resulting detector loop may then be connected to a suitable electronic intruder alarm located in an operation room distant from the fence, with the connecting cable desirably being carried underground.

In a long fence it might be considered desirable to 'sectionalise' the fence, i.e. to erect a series of shorter fences, each self contained with its own terminal strips and cable connected to the intruder alarm. Such sectionalised fences would offer an advantage, through the use of established switching techniques, in identifying the section being attacked.

An additional improvement to the fence is provided by an anti-climbing feature which ensures that an attempt to climb over the fence would cause the intruder alarm to be activated.

A specific embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: FIG 1. Illustrates in diagrammatic form a section of a plastic coated wire mesh fence incorporating detector loop and associated terminal posts.

FIG 2. Illustrates method of connecting detector loop to terminal strips located in terminal posts.

FIG 3. Shows fence post fitted with metal stanchion, with associated plug and socket assemblies and detector loop.

FIG 4. Illustrates, in cross section, a typical plug and socket assembly with associated detector loop connections.

FIG 5. Illustrates a wire-operated switch triggering device.

FIG 6. Shows an angled fence post incorporating anti-climbing cable.

A typical plastic-coated wire mesh fence is shown diagrammatically in FIG 1. Terminal posts 1 are fitted with terminal strips 2, these latter being used to connect the electrically conducting strands 3 to form detector loop which is connected to a suitable electronic intruder alarm (not shown) by cable 4.

FIG 2. illustrates in diagrammatic form a section of a terminal post showing the manner in which the cable assembly may be connected to terminal strips 2 to form combined closed-circuit and open-circuit detector loops.

Terminal posts are hollow box-like structures which contain the terminal strips and which could be constructed of concrete. Each post is provided with a metal cover plate secured by screwed bolts, and a suitable type switch connected in series with the closed-circuit detector loop. Matters are so arranged that the removal of the cover plate would automatically open the switch and cause the intruder alarm to be operated.

During the casting of the concrete posts shallow grooves could be-formed in the facing edges of the posts, of a pattern and dimensions compatible with that of the wire mesh, such as to closely accommodate the mesh pattern. When the metal cover plate is fitted to the post the wire mesh is thus firmly secured between post and cover plate.

Intermediate posts used solely to support the mesh fencing could be identical to the terminal posts but without the terminal strips. These intermediate posts could, however, be fitted with the switches mentioned above, connected in series with the closed-circuit detector loop network An anti-climbing feature of the invention will now be described, by way of example, with reference to FIG 3. Each post is fitted with a metal stanchion 5 provided with a number of holes into which are fitted plug and socket assemblies as shown in FIG 4.

The screwed nut 6 secures the socket body 7 to the stanchion. The plugs 8 are used to string an insulated wire or wires connected in series with the closed-circuit detector loop, along the length of the fence. FIG 3 shows a stanchion provided with two strands of cable, by way of example. Any attempt to climb over the fence would dislodge one of the plugs, thus breaking the circuit and activating the alarm.

A further example of an anti-climbing feature of the invention will now be described, with reference to FIG 5. A plastic covered wire 9 is carried under tension between the fence posts and a short distance above the wire mesh fencing. This wire, attached to the anchoring point 19 of the device located in the neighbouring post, is passed through the hole 10 and over the pulley wheel 20; it is then secured to the switch trigger 12 by the clamp 11. The switch trigger is free to move in a vertical plane in a guide slot (not shown) formed in the base plate 13, and is attached to the tensioning spring 14, which is in turn anchored to the base plate.

The switch trigger is provided with two protuberances which are designed to activate micro-switches 15 and 16.

Micro-switch 15 is fitted to the base plate as shown, such that should the wire 9 be cut then the switch trigger would, under the influence of the tensioning spring 14, be carried past micro-switch 15 which would be operated by the protuberance of the trigger, thus activating the intruder alarm.

Micro-switch 16 is fixed to a saddle and bar slide arrangement 17, or some other suitable arrangement, such that its position relative to the switch trigger 12 may be secured by means of the adjusting screw 18.

Matters are so arranged that should pressure be exerted on wire 9 by an attempt to climb over the fence, then the switch trigger would be drawn past micro-switch 16, thus operating the switch and activating the alarm. Both micro-switches in each post are connected in series with the closed-circuit detector loop.

Consideration is now given to the possibility that although the detector loop strands of the fence are visually indistinguishable from the other strands of the fence they might nevertheless be identified by an intruder and neutralised by the usual 'bridging and cutting' technique.

The following measures could be taken to prevent such identification.

If the detector loop strands of the fence were of copper wire, whilst the remaining strands of the fence were of ferrous metal, then a simple bar magnet could be used to identify the copper strands of the detector loop.

To prevent this, a strand of ferrous wire could be incorporated with the copper wire of the detector loop strands of the fence.

Electronic devices which are capable of indicating when an electrical conductor is carrying electric current are readily available, and such a device could be used to identify the current carrying strands of the detector loop, and action taken to neutralise them as indicated above.

This could be nullified by connecting in parallel all those fence strands not forming the detector loop, and passing through this parallel network an electric current equal to that being carried by the detector loop.

Claims (5)

1. A fence consisting of plastic-coated wire strands woven to form a mesh which is attached to posts sunk into the ground, certain strands being electrically series connected to form a continuous loop connected to a suitable electronic alarm designed to be activated if the loop is severed.

2. A fence as claimed in Claim 1 where the electrically conduct ing strands of the wire mesh are effectively aligned horizon tally with the ground and the loop strands are made by the use of terminal strips located inside hollow terminal posts.

3. A fence aS claimed in Claim 1 or Claim 2 where an insulated wire fitted with one or more plug and socket assemblies is strung along and some distance above the fence such that if undue pressure is exerted on the wire, which is in series with the loop, then one or more of the plug and socket assem blies would become disengaged.

4. A fence as claimed in any preceeding claim where a cable is strung along and some distance above the fence and which is attached to an electric switch in series with the loop such that any undue pressure exerted on the cable would break the electrical circuit of the loop.

5. A fence substantially as herein described and illustrated in the accompanying drawings.