GB2427769A

GB2427769A - Electric fence energisation system

Info

Publication number: GB2427769A
Application number: GB0612424A
Authority: GB
Inventors: Richard Lloyd Johnston; Ian Stuart Gallagher
Original assignee: Gallagher Group Ltd
Current assignee: Gallagher Group Ltd
Priority date: 2005-06-23
Filing date: 2006-06-22
Publication date: 2007-01-03
Anticipated expiration: 2026-06-22
Also published as: ZA200605178B; GB0612424D0; AU2006202703B2; AU2006202703A1; NZ540066A; GB2427769B

Abstract

Electric fence energisation system which includes at least two electric fence pulse generators. At least one pulse generator used is configured to emit an electric pulse of positive or negative polarity. A pulse generator also has at least one output configured to provide a pulse of opposite polarity to that emitted by one of the other pulse generators provided. Each of these pulse generators includes an energy storage element configured to supply at least one electric pulse, and a selectively conductive component adapted to provide at least part of a return path for electric pulses travelling in the opposite direction to an electric pulse supplied by the energy storage system.

Description

IMPROVEMENTS IN AND RELATING TO ELECTRIC FENCE SYSTEMS

IctINIcAL FIELD

This invention relates to improvements in and relating to electric fence systems.

Specifically the present invention may provide improvements within electrified security fences which have deterrent electrical pulses transmitted from conductors incorporated into the fence. In particular the present invention may be adapted to detect and prevent intruders from climbing such electrified security fences.

This invention also encompasses a fault detection apparatus and a method of operation for such an apparatus. Preferably the present invention may be employed to detect open circuit conditions on electric fence lines, where these fence lines are Incorporated into fencing systems with a comparatively high capacitive coupling of signals between adjacent fence lines and short circuits between adjacent wires supplied by separate pulse generators.

ACKGROUNDPJl.

Electrified fences are used in both agriculturj and security applications. Within security applications pulses of electrical current are transmitted down the conductors of a fence Periodically to deter unauthorjsed persons or intruders from either tampering with or climbing the fence provided. When an intruder touches an electrified conductor the intruder's body creates a path to ground and the intruder receives an electric shock.

Alarm systems are also generally linked to such electrified security fences and are used to alert security personne' to the presence of an intruder. These alarm systems can sense a drop in the voltage of deterrent pulses Which have been sunk to ground by the body of an intruder or by the shorting of two adjacent wires one carrying high voltage and the other at ground potentjaf Generally the alarm detection systems employed have an associated threshold level of voltage drop, where an alarm condition wilt only be positively detected if a voltage drop greater than such a threshold is detected.

In such configurations electrified fences in security applications generally have their live wires interleaved between adjacent earth wires. This configuration of fence system is vulnerable to tampering by intruders. If an earth wire is cut there will be no voltage drop experienced and therefore no alarm will be raised. This potentially could allow an intruder to climb the fence on the live wires only and experience no drop in voltage as they touch each live wire once their feet leave the ground. Conversely, if the live wires of the system are cut then this prevents deterrent pulses from being delivered to an intruder climbing the fence.

One approach used to alleviate these problems with intruders climbing electrified fences is through the provision of a bipolar fence energising scheme, in such applications alternate conductive wires of the fence are energised with electrical pulses with an opposite polarity to one another. In such instances the same amount of energy is driven along each alternate wire, but the potential difference or available voltage between alternate wires is double that of the voltage of each pulse measured in isolation. Furthermore as such bipolar systems do not include an Intervening earth wire, an intruder climbing the fence is still supplied with a deterrent shock irrespective of whether one live wire of the fence is cut.

Bipolar energisation schemes are usually created by using a centre tapped transformer. When more than one transformer is used there can be a problem with when the intruders feet leave the ground and they no longer provide an effective return path to sink the deterrent pulses. In the absence of such path no significant voltage drop is experienced or alarm condition detected.

Although this bipolar energising scheme does provide the potential to have a large voltage drop across alternate wires of a fence, in practice an intruder contacting adjacent wires will not trigger the effective grounding of pulses and hence the drop in voltage required to indicate an alarm condition has occurred. This limitation is due to that fact that a return path provided by only an intruder's body or other short circuit between wires must be found through the electrical components of the fence energiser circuitry opposite to that which generated the pulse to be earthed. In most instances an energiser pulse can be transferred over to an adjacent wire by a climbing intruder, but this pulse will still need to find a return path through or over a discharge transformer or transformer coupled trigger switch of the opposite energiser. This degraded return path will therefore result in a mild shocking effect being applied to an intruder and some potential difference drop being observed, but may not necessarily result in an alarm condition being detected.

An improved electric fence system which addressed any or all of the above issues would be of advantage over prior art. In particular an improved electric fence energiser system or circuit which provided an improved return path for pulses transiting the body of an intruder climbing an electric fence system would also be of advantage.

It is also important to promptly detect faults in electric fencing systems. With respect to electrified security fences, faults may be caused by unauthorised persons scaling, shorting out or cutting fence wires. In security fence applications it is important to quickly detect such tampering and prompt security personnel to investigate the state of the fence.

An important fault or condition to detect is an open circuit with respect to a security fence line conductor. An open circuit condition will indicate that a fence line has been cut, presumably by an intruder wishing to disable the fence. Such open circuits are normally sensed through measurement circuitry associated with the return path of the energjsecj conductor. This measurement circuitry is used to trigger an alarm if the output pulse of an energiser does not reach the return end of a line.

However, in some configurations of fence systems such open circuit detectors may be susceptible to false negative results where adjacent fence lines are close to one another and run over long distances. In such instances adjacent fence lines may be closely capacitively coupled together, so that an energiser pulse present on a first line may be coupled over to travel along a second adjacent line. This phenomenon can be a problem where one of the two lines has been cut, and due to the capacitive coupling effect an energiser pulse present on the adjacent uncut line will be coupled over to the open circuit line, then detected by the measurement circuitry associated with the return end of the cut line.

Bipolar fence energisation schemes have also been used in such security fence installations with long runs of conductors which are closely positioned with respect to one another.

However in some bipolar energisation security fence installations the length of the fence line results in a pulse shape modification. This situation can present a relatively high voltage over swing in the tail end of the pulse, which can be up to the same amplitude level as the start of the pulse but with an opposed polarity.

Due to the capacitive coupling between adjacent lines the presence of this over swing portion of a pulse coupled onto an adjacent line can again result in a false negative being detected by an appropriate open circuit measurement system. The voltage over swing of a coupled pulse can be effectively the same amplitude as the pulse expected by such open circuit detectors.

It would therefore be preferable to have an improved method, system or apparatus which addressed any or all the above problems associated with existing prior art fault detection systems. In particular a system, method or apparatus which could differentiate between real energiser pulses and capacitively coupled pulses from a nearby energised line would be of advantage.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

it is acknowledged that the term comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term comprise' shall have an inclusive meaning - i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term comprised' or comprising' is used in relation to one or more steps in a method or process.

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 ensuing description which is given by way of example only.

SCLOSURE OF INVENTION

According to one aspect of the present invention there is provided an electric fence energisation system which includes, at least two electric fence pulse generators, at least one pulse generator being configured to emit an electric pulse of positive or negative polarity, each pulse generator having at least one output configured to provide a pulse of opposite polarity to that emitted by one of the other pulse generators provided, each pulse generator including, an energy storage element adapted to Supply said at least one electric pulse, a selectively conductive component adapted to provide at least one part of a return path for electric pulses travelling in the opposite direction to an electric pulse supplied by the energy storage system.

According to a further aspect of the present invention there is provided an electric fence energisation system which includes 1.0 at least two electric fence energisers, at least one energiser being configured to emit an electric current pulse with a polarity opposite to that emitted by one of the other energisers provided, each energiser including, an energy storage element adapted to supply said at least one electric current pulse, and a primary transfer element connected to said energy storage element, and a secondary transfer element connected to an electric fence conductor, said primary transfer element being adapted to transfer an electric current pulse supplied by the energy storage element to an electric fence conductor through the secondary transfer element, and a selectively conductive component adapted to provide at least part of a return path for electric current travelling in the opposite direction to an electric current pulse supplied by the energy storage system.

The present invention is adapted to provide an electric fence energisation system which includes at least two electric fence pulse generators. Such pulse generators are configured to emit an electric pulse of positive or negative polarity.

Such electric fence pulse generators will each include one or more outputs to provide pulses of electrical energy.

In a further preferred embodiment each pulse energiser provided may be formed from or included within an electric fence energiser which includes primary and secondary transfer elements. However, in other embodiments such arrangements of primary and secondary transfer elements, and in particular transformers, need not be considered essential to the implementation of the present invention.

For example, some embodiments, the electric fence energisation system provided may include two or more electric fence energisers, or alternatively a single energiser with multiple output terminals where this energiser includes or incorporates two or more pulse generators. In such instances the pulse generators or the energisers provided may have their operations synchronised to control when each energiser or pulse generator fires.

In such embodiments the energy storage element provided within a pulse generator may be switched through an energy transfer device such as a transformer or alternatively directly onto an electric fence conductor. Those skilled in the art should therefore appreciate that the present invention may be implemented with at least two pulse generators, formed within a single energiser housing or two or more separate energisers.

Reference in the main throughout this specification to the use of transformers in conjunction with the present invention should therefore not be considered limiting.

Reference in general throughout this specification will also be made to the pulse generators provided being used to supply electric current pulses. However, those skilled in the art should also appreciate that pulses of current need not necessarily be supplied in isolation with respect to the present invention.

According to a further aspect of the present invention there is provided an electric fence energisation system substantially as described above wherein the selectively conductive component is connected across the primary transfer element of an electric fence energiser.

According to another aspect of the present invention there is provided an electric fence energisation system substantially as described above wherein the selectively conductive component Is connected across the secondary transfer element of an electric fence energiser.

According yet another aspect of the present invention there is provided an electric fence energisation system substantially as described above wherein the selectively conductive component provides at least part of a low impedance return path for electric current travelling from an electric fence conductor to the secondary transfer element of an electric fence energiser.

According to a further aspect of the present invention there is provided an electric fence energisation system substantially as described above wherein the selectively conductive component provides at least part of a low impedance return path for an electric current pulse with an opposite polarity to the electric current pulse supplied by the electric fence energiser.

According to an additional aspect of the present invention there Is provided an electric fence energiser substantially as described above wherein the selective conductivity of the selectively conductive component prevents current sourced from the energy storage element of the energiser from travelling through said selectively conductive component.

According to a further aspect of the present invention there is provided an electric fence energiser substantially as described above which also includes a discharge trigger element adapted to trigger the supply of an electric current pulse from the energy storage element.

According to yet another aspect of the present invention there is provided an electric fence energiser substantially as described above which forms at least part of a bipolar energisation system for an electric fence.

The present invention may preferably be adapted to provide an electric fence energising circuitry which may provide an improved low impedance return path for electric current travelling through to the output stage of the energiser from a fence line conductor. The present invention may also encompass the provision of an electrified fence system, preferably implemented as a security fence which incorporates a bipolar energisation system. In such instances the fence energisation circuitry provided may be adapted to transmit electric current pulses along alternate conductive wires of the fence where these pulses have a similar voltage amplitude but an opposite polarity to each other.

The present invention is configured to provide an energisation system for preferably two or more adjacent fence lines. Preferably such fence lines may be configured to form a bipolar energised fence system substantially as described above. Reference in general throughout this specification will be made to the components of a particular electric fence energiser incorporated into the electric fence energisation system required. However, those skilled in the art should appreciate that the energisation system of the present invention requires two or more of such appropriately configured electric fence energisers or pulse generators to operate effectively.

Preferably an energiser or pulse generator provided in accordance with the present invention may include at least one energy storage element. Such an energy storage element may be adapted to accumulate electrical energy to in turn periodically supply or deliver an electric current pulse to further components of the energiser. In a further preferred embodiment an energy storage element may be provided through at least one capacitor, which may be charged and then periodically discharged to supply the electric current pulses required.

Reference throughout this specification will also be made to an energiser or pulse generator provided including a single energy storage element only formed by a single capacitor. Again however, those skilled in the art should appreciate that other configurations are envisioned and also within the scope of the present invention.

Preferably an energiser provided also includes a primary transfer element which is connected to the energy storage capacitor and a secondary transfer element connected to a fence line conductor. The primary transfer element may be configured to transfer the energy of the electric current pulse supplied by the storage capacitor through to the security transfer element and on to a conductive wire of the fence to be energised. Preferably the primary transfer element may facilitate this transfer of energy through an indirect connection to the fence line involved via the secondary transfer element directly connected to the fence line. In such embodiments a deterrent electric current pulse may be induced onto a fence line from such a primary transfer element.

Reference throughout this specification will now in the main be made to the primary and secondary transfer elements being formed by the primary winding of a transformer which has its secondary winding directly connected to a fence line to be energised. Well known electric fence energising technology may be employed to implement such a transformer. However, those skilled in the art should appreciate that other approaches and components may also be employed to induce a deterrent electric current pulse onto a fence line, and reference to the above only throughout this specification should in no way be seen as limiting.

Preferably an energiser or pulse generator provided in accordance with the present invention may include a selectively conductive component. This selectively conductive component may be configured to provide an improved, lower impedance return path for electric current travelling in the opposite direction to a pulse supplied by the energy storage capacitor.

In such instances the selective conductivity of this component may therefore prevent current sourced from the discharged capacitor travelling along the path it provides.

Conversely due to the selective conductive nature of this component a conductive path may be opened to current travelling the opposite direction to that supplied by the discharged or discharging capacitor.

Preferably the selectively conductive component provided may be used to facifitate a an improved return path or path to ground for electric current travelling along a fence line connected to the energiser which reaches the secondary transfer element, or which is induced back over into the primary coil of the energisers transformer.

Preferably, this component may provide at least a portion of a lower impedance return path than that normally experienced by such current flows. This current will therefore be travelling in the opposite direction to that generated by the energy storage capacitor, and hence will be able to transit the selectively conductive path provided.

This selectively conductive path may present such current flows with a comparatively low impedance return path than that which would normally be encountered. As discussed above this characteristic of the present invention can be of advantage when the energiser is employed in a bipolar energisation scheme for a security fence.

The body of an intruder trying to climb up the fence contacting alternate wires may therefore provide a pathway across adjacent wires and therefore allow an energiser pulse travelling from one energiser to be returned with an improved efficiency via the opposite polarity energiser. This will in turn deliver an electric shock to the climbing intruder and result in a significant voltage drop being measured to trigger the detection of an alarm condition.

In a preferred embodiment a selectively conductive element may be formed from a diode or a serially connected "slack" of diodes. Diodes are well known in the art and may be connected within the energiser circuitry so as to present a high impedance to current flowing in one direction and a low impedance to current flowing the opposite direction.

Reference throughout this specification will also be made to the selectively conductive element employed being a diode. However, those skilled in the art should appreciate that other types of components which exhibit the same selectively conductive characteristics may also be employed in conjunction with the present invention and reference to the above only should in no way be seen as limiting.

Preferably a diode provided as a selectively conductive element may be connected across the primary winding of the energiser. This connection scheme may provide a low impedance path independent of the energy storage element and any discharge trigger elements provided with the present invention. In such embodiments the low impedance selective conductive path provided by the diode may run in a direction opposite to that of the current pulses sourced from the capacitor and being induced over the primary winding.

However, in an alternative embodiment the selectively conducve element may be a diode or stack of diodes connected across the secondary coil of each output pulse transformer. This diode or diodes may be arranged so as not to conduct when the main pulse from that transformer is being transmitted but to conduct when an opposite polarity pulse arrives on the fence connected to that transformer.

Furthermore in yet in an alternative embodiment where pulse generators but not energisers (or in particular transformers) are provided, the selectively conductive element will not necessarily be associated with such a primary transfer element or a secondary transfer element. For example, in such embodiments the selectively conductive element may be connected across a switching system and an energy storage or supply element.

In a preferred embodiment the present invention may also include a discharge trigger element which is adapted to trigger the supply of an electric current pulse from the energy storage capacitor. This discharge trigger element may be formed by any type of appropriate switching component, such as a physical switch, through to a semi- conductive switch such as a SCR (silicon controlled rectifier). In practice this discharge trigger will in turn provide a selectively conductive path for electrical current pulses supplied by the energy storage capacitor and may close a discharge circuit for the capacitor to allow It to discharge its charge, preferably through the primary windings of the transformer.

With prior art energisers the trigger element would form the part of the return path which pulses induced across from adjacent fence wires would need to transit. As can be appreciated by those skilled in the art these types of switch components would form a comparatively high impedance return path effectively blocking current flow in the reverse direction through the trigger device. Conversely, with the additional selectively conductive component provided in accordance with the present invention, the impedance of the return path experienced by such pulses may be substantially reduced. This in turn will allow a comparatively significant voltage drop to be experienced when two adjacent wires of a fence line are shorted together by an intruder, hence triggering the detection of an alarm condition and delivering an electric shock to the intruder.

According to one further aspect of the present invention there is provided a fault detection apparatus which includes, at least one input terminal configured to be electrically connected to a fence line conductor, said fence line conductor being periodically energised with electrical pulses, and at least one measurement element configured to assess a characteristic of an electrical pulse travelling along a fence line conductor connected to an input terminal, and a low pass filter element interposed between an input terminal and a measurement element, said low pass filter element being configured to remove high frequency signal components from an electrical pulse to be assessed by a measurement element.

According to yet another aspect of the present invention there is provided an electric fence energiser substantially as described above which includes a fault detection apparatus which incorporates, at least one input terminal configured to be electrically connected to a fence line conductor, said fence line conductor being periodically energised with electrical pulses, and at least one measurement element configured to assess a characteristic of an electrical pulse travelling along a fence line conductor connected to an input terminal, and a low pass filter element interposed between an input terminal and a measurement element, said low pass filter element being configured to remove high frequency signal components from an electrical pulse to be assessed by a measurement element.

The present invention is preferably adapted to provide a fault detection apparatus.

Preferably the present invention may be adapted for use with electric fencing systems, and may be engaged or interfaced with at least one fence line conductor, where such a conductor is periodically energised with electric pulses.

In a further preferred embodiment the present invention may be employed to provide an electric fence energiser which includes a fault detection apparatus substantially as described below. Such a fault detection apparatus may be incorporated into an energiser and have its input terminal or terminal connected to a return line or lines of the energiser.

Reference throughout this specification will also be made to the present invention being used to detect faults present within electric fence systems, and in particular electric fence systems which Include long conductor lines where these conductor lines are positioned relatively close to one another. However, those skilled in the art should appreciate that other configurations of the invention are also envisioned, and reference to the above only through out this specification should in no way be seen as limiting.

Preferably the fault detection apparatus provided includes at least one input terminal which is configured to be electrically connected to a fence line conductor. An input terminal can be used to terminate a fence line conductor, or to provide a signal tap point from a conductor to further components of the fault detection apparatus.

In a further preferred embodiment the apparatus provided may include an independent input terminal for each and every fence line conductor which is to have a fault detected or determined.

In a preferred embodiment the fault detection apparatus may include a measurement element which is to receive a pulse previously transmittedalong a fence line conductor. The measurement element may investigate at least one characteristic of a pulse from a conductor to determine whether a fault is present or associated with this conductor.

In a further preferred embodiment a measurement element may determine or detect the voltage and also polarity of the voltage amplitude and voltage polarity of an electrical pulse transferred from a conductor under investigation. As discussed previously the magnitude and polarity of a pulse received from the return end of the conductor can be assessed to indicate whether there is an open circuit condition associated with the conductor.

Reference throughout this specification will also be made to a measurement element employed in conjunction with the present invention being a polarity sensitive voltage measurement circuit. However, those skilled in the art should appreciate that other types of electrical pulse characteristics may also be measured in conjunction with the present invention, and reference to the measurement of the voltage magnitude and voltage polarity of a pulse throughout this specification should in no way be seen as limiting.

Preferably the fault detection apparatus may include a low pass filter element interposed between an input terminal and measurement element. Such a low pass filter element may be configured to remove high frequency signal components from an electrical pulse transmitted along a fence line conductor, through the input terminal, and finally to the measurement element. Such a low pass filter element may in effect damp out or potentially remove voltage under swing components present in capacitively coupled pulses generated within bipolar energisation systems.

In general terms the over swing component of such pulses will have a larger high frequency component than the initial energiser pulse component from a wire energised with a main pulse of opposite polarity. Such a low pass filter will therefore act to damp out the over swing which has been coupled to an adjacent wire, eliminating the potential for the measurement element to confuse this over swing voltage with a valid energiser pulse.

In bipolar energisalion schemes the measurement element may be sensitive to the polarity of a pulse, so that when a capacitively coupled pulse is detected the leading portion of the pulse will be the wrong polarity and hence will be ignored. The subsequent over swing portion of the pulse will in turn be damped out or down by the low pass filter, resulting in the valid detection of an open circuit condition if present on the fence line under investigation.

In a further preferred embodiment the low pass filter element may be configured to filter out signal frequencies greater than 16 kHz. In a further preferred embodiment such a filter element may begin to damp out or reduce the energy of signal components with frequencies greater than 12 kHz while effectively removing signals with frequencies greater than 16 kHz. In such embodiments the selection of high frequencies ranges effectively allows for the reduction or removal of voltage under swing from a pulse to be assessed.

Those skilled in the art will however appreciate that the low pass filter characteristics can further be determined empirically depending on the shape and frequency content of the electric pulse used for the particular topology of the energiser used and security fence installation concerned without departing from the scope of the invention.

BRIEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which: Ficiure I illustrates a block schematic diagram of an electric fence energisation system provided in accordance with a preferred embodiment of the present invention, and Figures 2a. 2b show two alternative schematic circuit diagrams of energiser circuitry components of the fence energisation system shown with respect to figure 1, and Figures 3a. 3b. 3c, 3d show voltage versus time plots of pulses to be assessed by a fault detection apparatus in accordance with one embodiment, and qures 4a. 4b show a fault detection apparatus configured with accordance with a further embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Figure 1 illustrates a block schematic diagram of an electric fence energisation system provided in accordance with a preferred embodiment of the present invention.

The fence system shown includes a bipolar energisation scheme, implemented through the provision of a pair of energisers (1, 2). The first energiser (1) is configured to transmit a positive voltage electric current pulse along the wire conductor (3) of the fence which terminates at measurement point (5). Conversely the second energiser (2) is adapted to transmit electric current pulses of a similar amplitude but with an opposite polarity to those delivered by the first energiser (1) through to fence line conductor (4) which terminates at measurement point (6). Each energiser (1, 2) also includes a pathway to ground.

As can also be seen in figure 1 an intruder attempting to climb the fence system or a tangled wire situation will present a short circuit, illustrated by the dotted reference line (7), across adjacent conductor (3). This will allow a positive pulse generated by energiser (1) to transit conductor (3), cross to conductor (4) and subsequently reach the output stage of energiser (2). For an effective voltage drop to be experienced, d this positive pulse will therefore need to find an effective return path via the circuitry of energiser (2). The same circumstances are present for negative polarity pulses generated by energiser (2) which are short circuited across to conductor (3) and which need to find a return path through the components of energiser (1).

Figures 2a and 2b show schematic circuit diagrams of alternative eriergiser circuitry components and electric current flows present within the fence system shown with respect to figure 1.

In the embodiment shown with respect with to figure 2a, the same positive pulse energiser (1) and negative pulse energiser (2) are illustrated. Each energiser includes a single energy storage element, implemented as a capacitor (8). A discharge circuit is provided for the capacitor through a primary winding (9) of a transformer to a discharge trigger element, shown in this embodiment as an SCR (11). When the SCR is fired a conductive path is therefore formed to allow the capacitor (8) to be discharge through the primary winding (9) to induce an electric current pulse into the secondary winding (10) of the energisers transformer, where the secondary winding is connected directly to the conductors of the fence system.

As can be seen from figure 2a the shorting of two alternate wires together by the body of an intruder climbing the fence system or the wires shorting together will result in the transmission of a pulse generated by one energiser through to the primary winding of the opposite energiser. To facilitate the improved or effective return of such pulses a further selectively conductive component is provided where this component is implemented in the embodiment shown through a diode (12). The diode (12) is connected across the primary winding of each energiser to provide a conductive pathway in the orientation shown - being from the output end of the primary winding (9) through to the output side of the capacitor (8).

As can also be seen from figure 2 the current pulses induced into an energiser from its opposite will normally have its return path blocked by the SCR (11) which is generally closed to facilitate the recharging of the capacitor (8). Conversely with the addition of the diode (12) current flows are shunted directly through the diode, bypassing the storage capacitor and SCR circuit. This configuration of energiser therefore implements an improved return path for such short circuited pulses and allows both the detection and deterrence of intruders climbing the fence system.

Conversely, figure 2b shows an alternative configuration to the energiser circuitry illustrated with respect to figure 2a. All the components of the circuitry shown are the same with the exception of the positioning of the diodes (12) now being across each of the secondary transformer colis (10).

As can be seen from figure 2b each of these diodes (12) will provide a selectively conductive low impedance path to energiser pulses from the opposite energiser shorted across the adjacent fence lines (3, 4). This low impedance path will therefore bypass the remaining components of the energiser involved, presenting the shorted pulse with a low impedance view of the energiser components.

Figures 3a, 3b, 3c and 3d show voltage versus time plots of pulses to be assessed by a fault detection apparatus in accordance with one embodiment.

Figures 3a and 3b illustrate original energiser pulses transmitted on two adjacent fence lines which employs a bipolar energisation scheme. As can be seen from figures 3a and 3b the same pulse is transmitted on adjacent lines but with reversed polarities. The positive polarity pulse shown with respect to figure 3a is transmitted along a fence line A, whereas the pulse shown with respect to figure 3b is transmitted along a fence line B. Figure 3c represents a pulse capacitively coupled onto fence line B when fence line B has been cut or experiences an open circuit condition. As can be seen from figure 3c this coupled pulse is slightly time retarded with respect to a valid energiser pulse and has an inverted polarity to that of a valid energiser pulse. As can also be seen from figure 3c the over swing, tail end portion of the pulse has a similar amplitude to the lead portion pulse but with an opposite polarity.

With existing polarity sensitive measurement systems the front section of the pulse of figure 3c will be ignored, whereas the over swing section of the pulse wib be mistaken for the lead section of a valid energiser pulse as represented with respect to figure 3b.

When the capacitively coupled pulse shown in figure 3c arrives at line B it is filtered by low pass filter components which results in the waveform shown in figure 3d appearing at point C illustrated with respect to figure 4b. The use of a low pass filter element acts to remove high frequency signal components to in turn damp out the voltage over swing section of the pulse. This can clearly be seen with respect to figure 3d where the leading section of the pulse is unaffected whereas the voltage over swing section is significantly damped.

Figures 4a and 4b show a fault detection apparatus configured with accordance with a further embodiment of the present invention.

In the embodiment shown the fault detection apparatus of figure 4a would be connected to the terminal point (5) of fence line (3) energised by energiser (1) of figure 1. Conversely, the detection apparatus of figure 4b can be connected to the terminal points (6) of fence line (4) energised by energiser (2) as illustrated in figure 1.

The input stage shown with respect to figure 4a is configured to receive and detect the presence of positive voltage polarity pulses, whereas the circuitry illustrated with respect to figure 4b is configured to deal with negative voltage polarity pulses.

The input stage shown includes an input terminal (20) connected to a series array of resistors (21, 22). Resistors 21 and 22 reduce the fence voltage (potentially up to 12000 volts) down to a manageable voltage for the remaining components of the measurement circuit shown and together with capacitor (27).form part of the low pass filter circuit (23) The low pass filter (23) is provided through the capacitor and resistor combination tuned to filter out signal frequencies of 16kHz and above.

An isolation system is then provided in the circuit through a protection diode (24) and an optical isolation diode (25). The optical isolation diode provides an optical output signal representative of the voltage pulse it receives at its input after this pulse has been filtered by the low pass filter stage (23).

The signal from the optical isolation diode is then analysed by a voltage magnitude and polarity measurement circuitry (26) to determine whether a valid energiser pulse has been received for the electric fence line associated with the input terminal (20).

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 WECLAIM IS: An electric fence energisation system which includes, at

least two electric fence pulse generators, each pulse generator configured to emit an electric pulse of positive or negative polarity, each pulse generator having at least one output configured to provide a pulse of opposite polarity to that emitted by one of the other pulse generators provided, each pulse generator including, an energy storage element adapted to supply said at least one electric pulse, and a selectively conductive component adapted to provide at least part of a return path for electric pulses travelling In the opposite direction to an electric pulse supplied by the energy storage system.
2. An electric fence energisation system which includes, at least two electric fence energisers, at least one energiser being configured to emit an electric current pulse with a polarity opposite to that emitted by one of the other energisers provided, each energiser including, an energy storage element adapted to supply said at least one electric current pulse, and a primary transfer element connected to said energy storage element, and a secondary transfer element connected to an electric fence conductor, said primary transfer element being adapted to transfer said electric current pulse supplied by said energy storage element to an electric fence conductor through the secondary transfer element, and a selectively conductive component adapted to provide at least part of a return path for electric current travelling in the opposite direction to an electric current pulse supplied by the energy storage system.
3. An electric fence energisation system as claimed in claim 2 wherein the selectively conductive component is configured to provide a selective conductive path across the primary transfer element of the energiser.
4. An electric fence energisation system as claimed in claim 2 or claim 3 wherein the selectively conductive component provides at least part of a low impedance return path for electric current travelling from an electric fence conductor through the primary transfer element.
5. An electric fence energisation system as claimed in claim 2 wherein the selectively conductive component is configured to provide a selective conductive path across the secondary transfer element of the energiser.
6. An electric fence energisation system as claimed in claim 5 wherein the selectively conductive components provides at leasi part of a low impedance return path for electric current travelling from an electric fence conductor to the secondary transfer element of the energiser.
7. An electric fence energisation system as claimed In any previous claim wherein an energy storage element is provided by at least one capacitor.
8. An electric fence energisation system as claimed in claim 7 wherein the selective conductivity of the selectively conductive component prevents current sourced from the capacitor from travelling through said selectively conductive component.
9. An electric fence energisation system as claimed in any previous claim wherein the selectively conductive component is formed by a diode.
10. An electric fence energisation system as claimed in any one of claims 2 to 9 wherein the primary transfer element transfers an electric current pulse to an electric fence conductor via a secondary transfer element directly connected to said electric fence conductor.
11. An electric fence energisation system as claimed In any one of claims 2 to 10 wherein a primary transfer element is formed by the primary winding of a transformer, said transformer having a secondary winding directly connected to a fence line conductor.
12. An electric fence energisation system as claimed in claim 11 wherein a diode provided as a selectively conductive element is connected across the primary winding of the transformer.
13. An electric fence energisation system as claimed in claim 11 wherein a diode provided as a selectively conductive element is connected across the secondary winding of the transformer.
14. An electric fence energisation system as claimed in daims 12 or 13 wherein said diode provides a low impedance conductive path for current travelling in a direction opposite to that of current pulses provided by the energy storage element of the energiser.
15. An electric fence energisation system as claimed in any previous claim which forms at least part of a bipolar energisation system for an electric fence:
16. An electric fence energisation system as claimed in claim 15 wherein adjacent electric fence conductors of said electric fence system are energised to carry electric current pulses with an opposite polarity to each other.
17. An electric fence energisation system as claimed in any previous claim wherein each pulse generator or energiser includes a discharge trigger element adapted to trigger the supply of an electric current pulse from the energy storage element.
18. An electric fence energisation system as claimed in claim 17 wherein the discharge trigger element is formed by a switch component. F
19. An electric fence energisation system as claimed in any previous claim which includes a fault detection apparatus.
20. An electric fence energisation system as claimed in claim 19 wherein the fault detection apparatus includes at least one input terminal configured to be electrically to a fence line conductor, said fence line conductor being periodically energised with electrical pulses, and at least one measurement element configured to assess a characteristic of an electrical pulse travelling along a fence hne conductor connected to an input terminal, and a low pass filter element interposed between an input terminal and a measurement element, said low pass filter element being configured to remove high frequency signal components from an electrical pulse to be assessed by a measurement element.
21. An electric fence energisation system as claimed in claim 20 wherein an input terminal is associated with a return line of an electric fence energiser.
22. An electric fence energisation system as claimed in claim 20 or claim 21 wherein a measurement element assesses the polarity and voltage amplitude of a pulse.
23. An electric fence energisation system as claimed in any one of claims 20 to 22 wherein a low pass filter element removes frequency signal components from an electrical pulse received at an input terminal.
24. An electric fence energisation system as claimed in any one of claims 20 to 23 wherein the low pass filter element is configured to filter out signal frequencies greater than 16 kHZ.
25. An electric fence energisation system as claimed in any one of claims 20 to 23 wherein the low pass filter element is configured to filter out signal frequencies greater than 12 kHZ.
26. An electric fence energisation system substantially as herein described with reference to and as illustrated by the accompanying drawings and/or

examples.