WO1996007316A1

WO1996007316A1 - Detecting fence wires deflection

Info

Publication number: WO1996007316A1
Application number: PCT/NZ1995/000080
Authority: WO
Inventors: John Veldman; Graham Harper
Original assignee: Gallagher Group Limited
Priority date: 1994-09-02
Filing date: 1995-08-31
Publication date: 1996-03-14
Also published as: AU3486995A

Abstract

A security device (9) for sensing deflection of a wire (3) of an electric fence relative to adjacent wires. The security device (9) including an electrically conductive contact element (10, 12, 13) or elements (10, 12, 13) mounted on a wire (3) or wires (3) and slidable along a non conductive guide tube (11), characterised in that where there is relative displacement of wires (3) towards each other, the contact element (10, 12, 13) comes into electrical contact with a wire (3) or an adjacent contact element (10, 12, 13) with substantially less deflection of the wires (3) than would otherwise be the case. The electrical contact between the contact elements (10, 12, 13) triggers an alarm indicating tampering of the electric fence.

Description

Detecting Fence wires deflection

TECHNICAL FIELD

This invention relates to a security device.

In particular, this invention relates to a security device which can sense the deflection of a wire on a electric fence.

BACKGROUND ART

Electric fencing is used in security applications for the protection of persons, animals and property. Typically, an electric fence may take the form of wires extending between uprights on the ground or uprights of security panels.

A change in impedance can indicate tampering with the electric fence wires. For example, cutting, earthing or shorting of wires all change impedance. These changes can be detected and the circuit formed by the wires may be arranged suitably so that a remote monitor which detects tampering may identify where the tampering of the fence has taken place.

However, there are problems associated with the system. This is because the wires of typical electric fences are flexible and can be displaced to some extent. A potential intruder may in some instances be able to force apart two adjacent wires to create a gap through which passage is possible. Thus, with the present security applications, non-detectable tampering with the electric fence is possible allowing intruders through. For example, it is possible for insulating ties to be used to tie together adjacent pairs of wires to allow a gap through which an intruder can pass easily.

Attempts have been made to address this problem. One attempt involved mounting of a conductive ring around an individual electrified wire. Movement of the wires would contact the ring causing a short. However, a problem with this method is that the system is too sensitive to poor fence construction as there is natural deflection of -the wires such as a consequence of say wind which could cause contact with the ring.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

Further aspects and advantages of the present invention will become apparent from the following description which is given by way of example only.

DISCLOSURE OF INVENTION

A security device for sensing deflection of a wire of an electric fence relative to adjacent wires,

the security device including an electrically conductive contact element or elements mounted on a wire or wires

characterised in that where there is relative displacement of wires towards each other, the contact element or elements comes into electrical contact with a wire or other contact elements with substantially less deflection of the wires than would otherwise be the case. According to a further aspect of the present invention these is provided a method of installing a security system having an electric fence characterised by the step of:

placing at least one contact element on the wire of an electric fence line which upon minimal deflection of that wire is capable of making electrical contact with another wire on that electric fence line.

Reference throughout this specification shall be made to the provision of at least one contact element per wire of the electric fence, although it should be appreciated that this should not be seen as limiting as some wires may not have a contact element.

The contact element may come in a variety of forms.

Preferably, the contact element extends from the wire to a distance that ensures that the contact element does not touch the other wire as a consequence of deflection caused by wind, but is of a size to contact the other wire if the wires are moved or deflected sufficiently to allow an intruder therethrough.

In some embodiments, the contact element may be a metal probe partially extending from one wire to the other wire. However, it is difficult to align a simple point contact like a probe with another wire. Further it may be possible to move the wires sideways with respect to each other and avoid making electrical contact through the probe.

Thus, in preferred embodiments there is either provided means to prevent movement of the wires sideways with respect to each other and/or more than a single point contact so as to increase the chances of electrical contact being made between the two wires. One way of achieving contact between the contact elements is to provide a guide along which the contact elements can move.

According to yet another aspect of the present invention there is provided a method of installing a security system having an electric fence characterised by the steps of :

a) placing at least one contact element on a guide, and

b) positioning the guide with respect to the wires of the electric fence so that at least one wire of the electric fence is capable of moving the contact element with respect to the guide.

The guide may take a variety forms, but in one embodiment the guide is a length of material which extends across all of the wires forming part of the electric fence or at least across the wires on which it is desired to measure deflection.

Again, the length of material may take a variety of forms but in one embodiment the length of material is tubing on a rod. Preferably the material from which the guide is made is lightweight so as not to place too much strain on the fence. Suitable materials from which tubing can be made include fibreglass and plastics.

In some embodiments of the present invention the guide may include tracks to which the contact elements are connected. The arrangement may be such that when the wire is deflected, the contact element moves along the tracks of the guide until it reaches the other wire (or contact element) to set off an alarm condition.

In preferred embodiments of the present invention the contact element encompasses part of the guide and can slide with respect to same. Thus, the contact element may be a sleeve, disc, or any other configuration which has enough contact points with the guide to guide the movement of the contact element to be controlled to some extent.

In preferred embodiments of the present invention the contact element is a helical member, although again it should be appreciated that this term is used only as an example of one embodiment.

Preferably the diameter of the helical member is such that it can slide readily along the guide, but still be close enough to the guide that it cannot be readily cut therefrom.

The helical member may be a conductive wire which is wound in such a fashion that it can slide readily around the guide. Use of a helical member has a number of advantages over other constructions. For example, the helical member uses less material than a solid sleeve and thus is relatively lightweight and inexpensive.

The helical member may be mounted to the wire by a variety of means.

In one embodiment, the wire may merely pass through the coils of the helical member.

However, in a preferred embodiment there is provided a wire locating section on the helical member. Preferably the locating section is situated substantially at the mid-point of the helical member so that the helical member extends a substantially equal distance either side out from the wire to which the helical member is attached.

The locating section may come in a variety of forms. In one embodiment of the present invention the locating section is formed as consequence of the way the helical member is wound. For example, the helical member may have two oppositely wound portions and the locating section may be defined by the transition between these portions.

It can be seen that by having a contact element extending from at least one wire (and preferably from all wires) which is guided to ensure that there is electrical contact between the wires on deflection overcomes a number of the problems associated with the prior art.

Firstly, there is a means to detect deflection of a wire with respect to another wire on an electric fence.

Secondly, the amount of deflection of the wires permitted before setting an alarm condition can be regulated by the size of the contact element on the wire.

Thirdly, alignment of the contact elements is ensured by the use of the guide.

Fourthly, the guide ensures that the wires cannot be moved sideways with respect to each other which could be another way through which an intruder may gain access.

While this embodiment is effective in most circumstances, it may be possible for an intelligent intruder to cut through the guide and remove the guide from the electric fence. Removal of the guide in this manner may allow the intruder to move adjacent wires away from each other and sideways with respect to the fence to avoid electrical contact thus creating a gap through which the intruder can pass.

To address this problem, in some embodiments of the present invention, the guide is hollow and capable of having a security wire extending along with inside of the guide. The security wire may be in electrical contact with one of the wires of the electric fence.

The above embodiment means that if the guide is at least partially severed with a tool such as a hacksaw, the security wire may make contact with the tool and thus providing a means by which tampering can be detected.

Alternatively, the guide may include a first security wire extending therethrough in electrical contact with one wire of the electric fence, and a second security wire extending therethrough in electrical contact with another wire of the electric fence. Preferably the security wires are not normally in electrical contact with each other inside the guide. Thus, if an intruder attempted to cut through the guide, the intruder will either ground one of the security wires or short the security wires together. Thus, this is a relatively simple way by which tampering can be detected.

BRrEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from the ensuing description which is given by way of example only and with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic view of one embodiment of the present invention position relative to an electric fence, and

Figure 2 is a diagrammatic view of an contact element in accordance with the above embodiment of the present invention, and

Figure 3 is a diagrammatic view of an alternate embodiment of the present invention on an electric fence, and

Figure 4 is a diagrammatic view of a contact element in accordance with another embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Figure 1 illustrates an electric fence generally indicated by arrow 1.

The electric fence 1 consists of electric fence posts 2 and electric fence wires 3.

Electric fence wires pass through insulators 4 on the posts 2.

Extending across the wires 3 is a security device generally indicated by arrow 5. The security device 5 consists of a rod 6 around which are positioned a number of contact elements 7 and electrically conductive restraint elements 8.

The restraint elements 7 are free to slide with respect to the tube 6 as the wires 3 are deflected.

The contact elements 8 are fixed to the tube 6 and secure the tube 6 to the top and bottom wires of the electric fence 1 to prevent twisting and thus prevent removal of the contact elements 7.

Figure 2 is a close up of a contact element 7 illustrated in Figure 1. The contact element 7 is helically shaped and maintains electrical contact with the wire 3 as a consequence of the wire 3 passing through the coils of the element 7. It can be seen that this arrangement ensures that the contact element on the wire 3 can slide with respect to the tube 6. However the wire 3 cannot move with respect to the contact element 7. Figure 3 illustrates an alternate security device 9 in accordance with the present invention.

Like the device 5 illustrated in Figure 1, the security device 9 includes a contact element 10 which encircles a guide in the form of a tube 11.

The construction of the contact element 10 is more clearly illustrated in Figure 4.

The contact element 10 comprises of two separate helical portions 12 and 13 which are wound in separate directions.

The transition between the portions 12 and 13 is a loop 14 which acts as a locating section for the wire 3.

The wire 3 .passes through the locating section 14 and when the wire 3 moves, the contact element 10 slides along the tube 11. When the contact element 10 comes into contact with another contact element, the wires 3 are electrically connected together and an alarm condition triggered.

The security device 9 includes a further feature not present in the security device 5.

This feature is the provision of two security wires 15 and 16 which extend from the top and bottom wires of the electric fence respectively. The wires 15 and 16 pass through the guide 11.

An intruder cutting the guide 11 is likely to cause the wires 15 and 16 to contact each other and thus set off an alarm condition.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.

Claims

WHAT WE CLAIM IS:

1. A security device for sensing deflection of a wire of an electric fence relative to adjacent wires,

characterised in that where there is relative displacement of wires towards each other, the contact element or elements comes into electrical contact with a wire or other contact elements with substantially less deflection of the wires than would otherwise be the case.

2. A security device as claimed in claim 1 which includes a guide along which the contact element can move.

3. A security element as claimed in claim 2 wherein the guide is a length of material which extends across the wires on which it is desired to determine deflection.

4. A security device as claimed in either claim 2 or claim 3 wherein the guide is in the form of tubing.

5. A security device as claimed in any one of claims 2 to 4 wherein the contact element encompasses part of the guide.

6. A security device as claimed in any one of claims 1 to 5 wherein the contact element is a helical member.

7. A security device as claimed in any one of claims 1 to 6 wherein the contact element includes a wire locating section.

8. A security device as claimed in any of claims 2 to 7 which includes at least one wire which passes through the guides.

9. A method installing a security system characterised by the step of

10. A method of installing a security system characterised by the steps of;

a) placing at least one contact element on a guide, and

11. A security device substantially as herein described with reference to and as illustrated by the accompanying drawings.

12. A method of installing a security system substantially as herein described with reference to and as illustrated by the accompanying drawings.