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Title:
FENCE CONDITION MONITORING APPARATUS AND METHOD
Document Type and Number:
WIPO Patent Application WO/2004/095893
Kind Code:
A1
Abstract:
The invention provides a monitoring apparatus adapted to monitor the condition of a fence line (4). It includes a reference signal generator (1), and an interface adaptor (2) configured to place a reference signal on a fence line. This interface adaptor has a connection to the reference signal generator which provides isolation of the reference signal generator from the fence line, the interface adaptor places a reference signal on the fence line remote from the location of an electrical load (6) present on the fence line. The monitoring apparatus also includes a detection system (3) to receive a translated signal from the interface adaptor where this detection system has a connection to the interface adaptor which provides isolation of the detection system from the fence line. The system indicates the condition of the fence line monitored through the state of one parameter associated with a translated signal received by the detection system.

Inventors:
Johnston, Richard Lloyd (19 Sandalwood Drive, Hamilton, 2001, NZ)
Application Number:
PCT/NZ2004/000076
Publication Date:
November 04, 2004
Filing Date:
April 20, 2004
Export Citation:
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Assignee:
GALLAGHER GROUP LIMITED (PO Box 3026, Kahikatea Drive Hamilton, 2001, NZ)
Johnston, Richard Lloyd (19 Sandalwood Drive, Hamilton, 2001, NZ)
International Classes:
A01K3/00; H05C3/00; G01R31/02; (IPC1-7): H05C1/00; A01K3/00; G01R31/02
Foreign References:
US4297633A1981-10-27
US5651025A1997-07-22
Other References:
DATABASE WPI Derwent Publications Ltd., London, GB; Class S01, AN 1994-176649, XP002904872 & ZA 9 205 549 A (JENKINSON) 30 March 1994
Attorney, Agent or Firm:
Murphy, Simon J. (Private Bag 3140, Level 12 KPMG Centre, 85 Alexandra Stree, Hamilton 2001, NZ)
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Claims:
CLAIMS :
1. A monitoring apparatus adapted to monitor the condition of a fence line, said monitoring apparatus including a reference signal generator, and an interface adaptor having a connection to a fence line to be monitored, said interface adaptor having a connection to the reference signal generator which provides isolation of the reference signal generator from the fence line, wherein said interface adaptor is configured to place a reference signal generated by the reference signal generator on the fence line at a point remote from the location of an electric load present on said fence line, and a detection system adapted to receive a translated signal from the interface adaptor, said detection system having a connection to the interface adaptor which provides isolation of the detection system from the fence line, wherein the detection system is adapted to indicate the condition of the fence line monitored through the state of at least one parameter associated with the translated signal.
2. A monitoring apparatus as claimed in claim 1 wherein the fence line monitored is adapted to carry high voltage pulses.
3. A monitoring apparatus as claimed in either claim 1 or claim 2 wherein the voltage of the reference signal is within or below a safe voltage value defined by published standards.
4. A monitoring apparatus as claimed in claim 3 wherein the reference signal voltage is between 142 volts.
5. A monitoring apparatus as claimed in any previous claim wherein the reference signal is formed from an alternating current signal.
6. A monitoring apparatus as claimed in claim 5 wherein the reference signal frequency is between 100 Hz and 5 kHz.
7. A monitoring apparatus as claimed in either claim 5 or claim 6 wherein the reference signal frequency is between 1 kHz to 2 kHz.
8. A monitoring apparatus as claimed in any previous claim wherein the remote electrical load presents an inductive load to an alternating current signal.
9. A monitoring apparatus as claimed in any previous claim wherein the remote electrical load presents a capacitative load to an alternating current signal.
10. A monitoring apparatus as claimed in any previous claim wherein the remote electrical load presents a resistive load to an alternating current signal.
11. A monitoring apparatus as claimed in any previous claim wherein the remote electrical load is an electric fence energiser.
12. A monitoring apparatus as claimed in claim 11 wherein the monitoring apparatus is located at the return end of the fence line monitored.
13. A monitoring apparatus as claimed in any previous claim wherein the interface adaptor is formed from an electrical transformer.
14. A monitoring apparatus as claimed in claim 13 wherein the interface adaptor is formed from a high voltage insulated electrical transformer.
15. A monitoring apparatus as claimed in any one of claims 13 or 14 wherein the interface adaptor includes protection components.
16. A monitoring apparatus as claimed in any previous claim wherein the detection system considers the voltage of a received translated signal.
17. A monitoring apparatus as claimed in any previous claim wherein the detection system includes peak detection circuitry.
18. A monitoring apparatus as claimed in any previous claim wherein the detection system includes at least one voltage comparator, said at least one comparator being supplied with a reference threshold signal and a translated signal.
19. A monitoring apparatus as claimed in any one of claims 16 to 18 wherein the detection system compares a received translated signal voltage with an upper voltage threshold value and a lower voltage threshold value.
20. A monitoring apparatus as claimed in claim 19 wherein the upper voltage threshold value is selected depending on the load of the fence fine monitored under normal operating conditions.
21. A monitoring apparatus as claimed in claim 19 wherein the lower threshold voltage value is selected depending on the impedance of the remote electrical load on the fence line.
22. A monitoring apparatus as claimed in any one of claims 19 to 21 wherein a threshold reference voltage value is varied using a rolling average.
23. A monitoring apparatus as claimed in any one of claims 19 to 21 wherein a threshold reference value is determined by a threshold rate of change for a parameter.
24. A method of monitoring the condition of a fence line characterised by the steps of: (i) placing a reference signal on a fence line using an interface adaptor, wherein the interface adaptor is configured to place the reference signal on the fence line at a point remote from the location of an electric load present on said fence line, and (ii) receiving a translated signal from the interface adaptor with a detection system, said detection system having a connection to the interface adaptor which insulates the detection system from the fence line, and (iii) indicating the condition of the fence line using the state of at least one parameter associated with the translated signal received. A method of monitoring the condition of a fence line as claimed in claim 24 wherein the condition of the fence line is indicated by comparing a parameter associated with the translated signal received with a threshold parameter value. A method of monitoring the condition of a fence line as claimed in claim 25, wherein the condition of the fence line is indicated through comparing the voltage of the received translated signal with an upper threshold voltage value and a lower voltage threshold value. A method of monitoring the condition of a fence line as claimed in claim 26, wherein the upper voltage threshold value is selected depending on the load of the fence line monitored under normal operating conditions. A method of monitoring the condition of a fence line as claimed in claim 26, wherein the lower threshold voltage value is selected depending on the impedance of the remote electrical load on the fence line.
25. A method of monitoring the condition of a fence line as claimed in any one of claims.
26. to 28 wherein a threshold reference voltage value is varied using a rolling average of previous translated signal voltages. A method of monitoring the condition of a fence line as claimed in any one of claims 25 to 28 wherein a threshold reference value is determined by a threshold rate of change for a parameter. A method of monitoring the condition of a fence line characterised by the steps of : (i) placing a reference signal on a fence line using an interface adaptor wherein the interface adaptor is configured to place the reference signal on the fence line at a point remote from the location of an electric load present on said fence line, and (ii) receiving a translated signal from the interface adaptor with a detection system, said detection system having a connection to the interface adaptor which insulates the detection system from the fence line, and (iii) comparing the voltage of the translated signal with an upper threshold voltage value and providing an alarm signal if said translated signal voltage is greater than the upper threshold voltage value, and (iv) comparing the voltage of the translated signal with a lower threshold voltage value and providing an alarm signal if said translated signal voltage is less than the lower threshold voltage value. A monitoring apparatus substantially as herein described with reference to and as illustrated by the accompanying drawings and/or examples.
27. 33 A method of monitoring the condition of a fence line substantially as described with reference to and as illustrated by the accompanying drawings and/or examples.
Description:
FENCE CONDITION MONITORING APPARATUS AND METHOD TECHNICAL FIELD This invention relates to an improved method and apparatus for detecting faults or changes in the condition of an electrified fence. Preferably the present invention may be adapted to monitor the condition of the fence both during periods of energisation of the fence and periods in which the fence is not energised.

Furthermore the present invention may also be adapted to monitor the condition of an electrified security fencing in preferred embodiments.

BACKGROUND ART Fences and other similar types of barriers have been developed which can carry periodic electrical voltage and current pulses. The amplitude of the electrical pulses transmitted along wires incorporated into a fence can cause a painful shock and are commonly used in livestock control and security applications.

For electrified or electric fences used as security barriers, it is critical for the operator or maintainer of the fence to be aware of any changes in the condition of the fence and the wires or lines which carry the deterrent electric pulses employed.

Changes in the condition of the fence and the continuity of these transmission lines or wires can indicate an unauthorised attempt to gain access to the area protected by the fence. Changes in the condition of the fence may also indicate accidental damage has occurred or that the condition of the lines involved and their effectiveness have deteriorated slowly due to natural factors.

Electrified security fences are often deactivated during daylight hours when the area the fence protects is normally accessible to authorised personnel and in some instances the general public, who could inadvertently come in contact with

electrified wires of the fence. During times when the fence is not electrified, there is the potential for materials to be stacked against and in contact with the fence or for vehicles to be parked in contact or in close proximity to the electrified wires.

Furthermore, in time periods when a security fence is deactivated, there is the potential for an unauthorised person to cut, damage or otherwise tamper with the fence line without being exposed to a high voltage pulse from the lines they are tampering with.

These situations are usually only detected once the fence line is energised.

Generally, discovery of these problems will occur during times at which the area secured is unoccupied and other similar times in which it will be difficult and inconvenient to rectify the situation.

One current method of monitoring the state of an electric fence is through monitoring the type, form or parameters associated with the particular electric fence pulses or alternating current waveforms driven through the electrified wires.

Changes in the parameters of these signals or transmissions will indicate a change in the impedance of the fence wire, as a consequence of a change in the condition of the fence wire.

However, monitoring the voltages on the high voltage electrification line or deterrent wire does not necessarily allow the condition of the fence line to be monitored when the fence is not energised. Furthermore, these types of monitoring approaches are susceptible to false alarms caused by gradual changes in the condition of the fence. These gradual changes can be caused by vegetation growth slowly coming into contact with the deterrent wire or through gradual changes in the physical condition of the fence, all of which can change the impedance of the deterrent wire or line and subsequently trigger false alarms.

An alternative approach to the above is to provide an additional wire in the fence

through which a low voltage direct current signal is transmitted. Tampering with the fence may result in this'tamper evident'wire or line being cut with the subsequent interruption of the DC signal driven down the line being indicative of tampering occurring with the fence.

Again however, this approach does not necessarily solve all the problems associated with monitoring such electrified fences or electric fences. A separate low voltage tamper line may not necessarily be cut or damaged at the same time at which a high voltage deterrent or live wire is cut or tampered with. Furthermore, the use of a relatively low voltage DC electrical signal can cause electrolysis effects and result in degradation of the quality of connections to the DC line. This degradation will subsequently change the impedance of the line involved and hence again potentially trigger a false alarm being detected.

It would be preferable to have an improved method and/or apparatus for monitoring the condition of an electrified fence which addressed any or all of the above problems. Preferably, a method or apparatus which could monitor the state of an electrified fence in time periods when the fence is not electrified or energised and also in periods in which the fence was electrified or energised 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.

DISCLOSURE OF INVENTION According to one aspect of the present invention there is provided a monitoring apparatus adapted to monitor the condition of a fence line, said apparatus including a reference signal generator, and an interface adaptor having a connection to a fence line to be monitored, said interface adaptor having a connection to the reference signal generator which provides isolation of the reference signal generator from the fence line, wherein said interface adaptor is configured to place a reference signal generated by the reference signal generator on the fence line at a point remote from the location of an electric load present on said fence line, and a detection system adapted to receive a translated signal from the interface adapter, said detection system having a connection to the interface adapter which

provides isolation of the detection system from the fence line, wherein the detection system is adapted to indicate the condition of the fence line monitored through the state of at least one parameter associated with the translated signal.

According to a further aspect of the present invention there is provided a method of monitoring the condition of a fence line characterised by the steps of; i) placing a reference signal on a fence line using an interface adapter, wherein the interface adapter is configured to place the reference signal on the fence line at a point remote from the location of an electric load present on said fence line, and ii) receiving a translated signal from the interface adapter with a detection system, said detection system having a connection to the interface adapter which insulates the detection system from the fence line, and iii) indicating the condition of the fence line using the state of at least one parameter associated with the translated signal received.

According to a further aspect of the present invention there is provided a method of monitoring the condition of a fence line substantially as described above wherein the condition of the fence line is indicated by comparing a parameter associated with the translated signal received with a threshold parameter value.

According to a further aspect of the present invention there is provided a method of monitoring the condition of a fence line characterised by the steps of; i) placing a reference signal on a fence line using an interface adapter, wherein the interface adapter is configured to place the reference signal on the fence line at a point remote from the location of an electric load present on said

fence line, and ii) receiving a translated signal from the interface adapter with a detection system, said detection system having a connection to the interface adapter which insulates the detection system from the fence line, and iii) comparing the voltage of the translated signal with an upper threshold voltage value and providing an alarm signal if said translated signal voltage is greater than the upper threshold voltage value, and iv) comparing the voltage of the translated signal with a lower threshold voltage value and providing an alarm signal if said translated signal voltage is less than the lower threshold voltage value.

Preferably the present invention is adapted to provide a monitoring apparatus and method which can be used to monitor the condition and state of an electric fence line. Preferably the electric fence line monitored is adapted to carry high voltage pulses or high voltage alternating currents to serve as a deterrent against an unauthorised person wishing to breach the fence. Preferably the present invention may be used to monitor the condition of such electrified lines and also indicate whether such lines have developed a fault, or have been tampered with in such a way that they can no longer effectively carry the electrical transmissions required.

Reference throughout this specification will also be made to the present invention being adapted to detect or indicate the presence of a fault in an electric fence line which will prevent or hamper the line from carrying electrical transmissions.

However, those skilled in the art should appreciate that the present invention may also be employed to provide general information with respect to the basic condition of the fence line, which need not necessarily focus on just the presence of a fault or tampering with the line.

Those skilled in the art should also appreciate that the fence line to be monitored should be considered as insulated from any supporting members (or preferably fence posts) used to elevate and separate any fence wires employed. Those skilled in the art should appreciate that the fence line involved should be insulated from contact from such structural supporting members wherever possible to allow effective operation of the fence provided.

Preferably the present invention includes a reference signal generator. This component is adapted to generate a reference signal to in turn be placed on the fence line to be monitored. Preferably an electrical reference signal may be generated with known characteristics where the condition and physical properties of the fence line will in turn alter or modify these characteristics to result in a translated signal. Placing the reference signal on the fence line will immediately result in the production of the translated signal propagating along the fence line due to the physical characteristics and condition of the fence line. The degree of alteration or modification of the reference signal as measured in or presented by the translated signal produced will then provide an indication as to the condition or state of the fence line monitored. Those skilled in the art should appreciate that references to a translated signal as discussed above do not relate to a simple D. C. offset applied to a reference signal.

In a further preferred embodiment, a relatively low voltage reference signal may be produced by the reference signal generator. Preferably the reference signal applied may have a voltage which is below the threshold of sensation for the average person. Furthermore, the voltage of the reference signal may preferably be within or below a safe voltage value as defined in existing published electric fence standards.

For example, a voltage level below that established in the following standards

would be preferable for use with the present invention- International Electrotechnical Commissions standards; IEC 60479-1: 1994 (third edition) Part I General Aspects (1994-09) IEC 60479-2: 1987 Part II Special Aspects (1987-03).

In a preferred embodiment the voltage of the reference signal applied maybe between 1-200 volts, and preferably between 1-42 volts.

The use of a relatively low voltage reference signal ensures that the transmission of the reference signal to the fence line will not cause safety concerns or issues for persons in the vicinity of the fence line who potentially may come into contact with same. Preferably the present invention may be adapted to monitor the condition of a fence line without necessarily having the same fence line energised by high voltage electrical pulses. The use of a low voltage reference signal will then allow the fence line to be monitored without causing safety concerns to those in the vicinity of the line.

In a further preferred embodiment, the reference signal may be formed from an alternating current or sinusoidal waveform type signal. AC waveforms have distinct and easily measured electrical properties or parameters and can also be easily generated using existing signal generation components. Furthermore, a relatively low power AC reference signal may be employed to achieve the aims of the present invention while minimising the energy consumption costs associated with operating the monitoring apparatus.

Reference throughout this specification will also be made to the reference signal employed being formed from a low voltage alternating current electrical signal.

Furthermore, such a reference signal may be generated using known electrical signal generation circuitry and components well known in the art. For example, in

one preferred embodiment, a reference signal generator may be implemented through the use of a microprocessor adapted to produce a square wave signal which can subsequently be shaped or formed into a standard sine wave alternating current signal by various signal filtering components or systems. However, those skilled in the art should also appreciate other types of signals and other types of signal generation systems may also be employed and reference to the above only throughout this specification should in no way be seen as limiting.

Preferably the present invention may also include an interface adapter which is adapted to interface the other remaining components of the monitoring apparatus with the fence line to be monitored. Preferably the adapter may provide isolated connections to other components of the apparatus where these connections provide such components with electrical isolation from the electric fence line monitored.

In a further preferred embodiment, the interface adapter may be adapted to place the reference signal on the fence line at a position remote from the location of an electrical load on the same fence line. This configuration of the monitoring apparatus ensures that the characteristics of a translated signal supplied to the detection system will change substantially if the fence line is short circuited or open circuited between the connections of the electrical load involved and the interface adapter provided. Such significant changes in the impedance or resistance met by the reference signal will then provide a clear indication of changes in the condition of the fence line monitored.

In a preferred embodiment, the monitoring apparatus provided may be located at the return or terminating end of the fence line monitored. This location on the fence line may be defined as the opposite end of the line to an energiser used to transmit high voltage pulses along the line, or alternatively the opposite end to any

other type of electrical load placed on the same line as the monitoring apparatus.

In a preferred embodiment the impedance of the electrical load remote from the monitoring apparatus may be substantially greater than the impedance of the fence line to be monitored.

An electrical load located remote from the return end of the fence line monitored may be formed from a capacitive, inductive or resistive load if required depending on the specific implementation with which the present invention is employed.

Reference throughout this specification will also be made to the electrical load located remote from the location at which the interface adapter as being components or elements of an electric fence energiser or the entire energiser itself.

Such energisers are normally employed to place high voltage pulses or electrical transmissions on a fence line. The impedance or load produced by such an energiser, and whether or not this load is experienced by the reference signal placed on the line will provide a clear indication as to the condition of the fence line monitored.

In a further preferred embodiment the remote electrical load involved may form an inductive load to an alternating current signal. This selection can be made so that the resistive impedance of the fence line (formed by the length of fence, bad joints etc. ), has less effect on the overall impedance of the monitored system, while the inductive component is the dominant component of the impedance.

In a further preferred embodiment changes in the resistive impedance of the system may be discriminated from the end of line inductance. This provides improvements to immunity against variances in fence installations over existing resistive sensing systems.

However, those skilled in the art should appreciate that any other type of electrical

load may also be employed in conjunction with the present invention and reference to the load being provided through an electrical fence energiser only should in no way be seen as limiting. Furthermore, reference will also be made to the interface adapter placing a reference signal at a terminating end of a fence line where the electric fence energiser involved is located at the opposite end of such a fence line.

This configuration of the invention allows the entire length of the fence line to be monitored, but again those skilled in the art should appreciate that location of components of the present invention at one, or the extreme opposite ends only of a fence line should in no way be seen as essential.

In a further preferred embodiment, the interface adapter may be formed from or include an electrical transformer. A transformer can be used to block the relatively high voltage electrical pulses normally transmitted along the electric fence line during standard operation to prevent damage to other components employed in conjunction with the present invention. Furthermore, the isolated windings of such a transformer may be used to allow a reference signal to be applied to, for example, the primary winding and be induced onto the fence line through the secondary windings of the transformer. Conversely a translated signal present on the fence line (due to the induction of the reference signal onto same) may be induced across the secondary windings of the transformer onto the primary windings to subsequently be detected or received by a detection system.

In a preferred embodiment the interface adaptor may also include protection or limiting components if required. Such protection components may be used to protect further elements of the monitoring apparatus provided from high energy pulses or signals present on the fence line monitored. Such protection components may damp out or dissipate the energy present in such pulses or signals prior to further components of the monitoring apparatus being exposed to same.

Preferably a transformer used as or in an interface adaptor may also be insulated to a specific standard or degree to cope with a high voltage pulses transmitted along the fence line and thereby allowing the transformer to subsequently protect the remaining components of the monitoring apparatus employed from damage. In a further preferred embodiment, a transformer employed in conjunction with the present invention may be provided through a high voltage insulated electrical transformer. Such a transformer is normally specifically adapted to be used with electric fences carrying high voltage pulses typically in the order of 6-10 kV, and can provide approximately 20 kV of isolation between a primary and secondary windings.

Reference throughout this specification will also be made to the interface adapter employed being provided through an electrical transformer. Reference will also be made to the additional components of the present invention being provided with connections to the primary winding of such a transformer, with the fence line to be monitored connected to the secondary winding.

However, those skilled in the art should appreciate that other types of interface adapter which again provide the same degree of isolation may also be used in conjunction with the present invention. For example, in one alternative embodiment, optical isolation systems and adapters may be used to present a reference signal to the fence line and subsequently retrieve a translated signal from the same fence line if required. Those skilled in the art should appreciate that reference to electrical transformers only throughout the specification should in no way be seen as essential in the implementation of the present invention.

Preferably the present invention may include a detection system adapted to receive a translated signal and a subsequently indicate the condition of the fence line monitored. Such a detection system may preferably provide an indication of the

fence line's condition through an alarm buzzer, warning light or any other type of alert signal which is triggered through the detection of a fault in the fence line or through the detection of tampering having occurred to the fence line. Alternatively, the alarm signal of a detection system may be used to control or operate further independent equipment or devices.

Reference throughout this specification will also be made to the detection system being employed to provide a simple alarm indicator or alarm signal upon the detection of a fault in or tampering with the fence line. However, those skilled in the art should appreciate that the characteristics of the translated signal may also be investigated to provide general information regarding the condition of the fence line-not necessarily just associated with a fault or tampering of the line-and reference to the above only throughout this specification should in no way be seen as limiting.

In a further preferred embodiment, the detection system may be provided with a connection to the primary winding of an interfacing transformer where the secondary winding of the transformer is connected to the fence line. The connection to the primary winding may then allow an induced translated signal to be read or received from the primary winding where this translated signal is used as an input to the detection system.

Preferably the detection system is adapted to investigate or consider the state of at least one parameter associated with a received translated signal. Preferably an amplitude, level, power or energy value associated with a particular parameter may be investigated to determine the state of the fence line monitored. Those skilled in the art should appreciate that many different and varied parameters such as voltage, current, signal frequency or phase angle may all be employed if required in various embodiments to indicate the state of the fence line.

In a further preferred embodiment the voltage of the translated signal may be considered to determine whether a fault or tampering event has occurred with respect to the fence line monitored. The voltage of the translated signal may be compared with at least one threshold voltage value, and an alarm condition may be indicated if the measured translated signal or voltage is less than or greater than a specific threshold value.

In one preferred embodiment the detection system may be implemented through or at least include one or more comparator circuits. A comparator may be provided with a reference threshold voltage and the voltage of the translated signal as inputs where the output of the comparator (being either voltage high or ground) will indicate whether a fault or tampering condition has occurred.

In a further preferred embodiment, the detection system may also include peak detection circuitry in the case where the original reference signal employed is formed from alternating current waveforms. Such peak detection circuitry may convert the received alternating current translated signal into a direct current signal with a specific voltage value or parameter. This D. C. signal may then be easily managed or manipulated using standard analogue or digital circuitry.

In a preferred embodiment, the voltage measured for the translated signal may be compared against two separate and distinct threshold voltage values. In such instances the condition of the fence line monitored will be acceptable when the voltage measured resides between an upper and a lower voltage threshold for the received translated signal. Preferably two distinct threshold voltage comparisons are made to monitor situations where the impedance of the fence line monitored has increased or reduced. Either of these two conditions can indicate the presence of a fault in the line or that tampering of the line has occurred.

The investigation of two distinct upper and lower threshold voltage tests allows the

impedance of the fence line involved to be monitored. If the voltage of the translated signal increases substantially, this will indicate that the impedance of the fence line has risen and less current is being drawn. Conversely if the translated signal voltage drops, this will indicate that the impedance of the line has reduced, to an increased current being drawn. An increased impedance of the line will therefore indicate that potentially an open circuit has occurred which can indicate that the line has been cut or tampered with. Conversely, a reduced impedance will indicate the presence of a short circuit, through for example, additional loads being placed on the line by vegetative growth coming in contact with the line, or alternatively tampering occurring.

Furthermore, when the present invention is located at one end of a fence line with the energiser circuitry load at the opposite end of the line, a short or open circuit will drastically change the impedance of the line experienced by the reference signal when placed on the line. This therefore will provide an obvious and clear indication as to the change in state or condition of the line.

In one embodiment of the present invention, one or more variable threshold parameters may be used in the comparisons made to monitor the state of the fence line involved. The actual threshold parameter to which a comparison is made may be adjusted or modified to take into account gradual changes in the state of the fence line. These changes could be caused by, for example, vegetative growth, gradual oxidation of metallic components of the fence or any other factors which will slowly and gradually change the condition of the fence line.

In one preferred embodiment, one or more rolling average threshold voltage values may be maintained to track gradual changes in the condition of the fence which do not necessarily indicate tampering or a fault condition. For example, in some instances a rolling average of the translated signal may be maintained with the

threshold value set at plus or minus 20% of a current rolling average or voltage value.

However, in an alternative embodiment, gradual changes in the condition of the fence line may be compensated for by using mechanisms other than the rolling average technique discussed above. For example, in one alternative embodiment, the rate of change of voltage, current or other similar electrical parameters associated with the translated signal may be measured and used as a threshold value. A significant rate of change in one of the characteristics of the translated signal will therefore indicate fault or alarm condition, as opposed to changes made through more gradual factors.

An upper bound frequency of this signal may be selected depending on the load of the fence line monitored under normal operating conditions. For example, in some instances the normal load of the fence line may be estimated and an additional margin of error of, for example, 20% can be added to this load value to determine a threshold voltage for when the load of the fence increases by approximately 20% or more.

Furthermore, a lower threshold voltage value may be selected depending on the impedance of a remote electrical load (preferably being an energiser) on the fence line to be monitored.

In a preferred embodiment where an alternating current reference signal is employed, the frequency of this reference signal may be selected depending on the characteristics and configuration of the fence line to be monitored.

An upper bound frequency of this signal will be determined by the potential resonant frequency of the fence line or lines with which the present invention is to be employed. In the vicinity of the resonant frequency the impedance of the line is

at its larges. Furthermore, there is the potential for this resonant frequency to shift randomly due to small physical movements in the position of the line caused by wind for example, or through the proximity of metallic objects (such as vehicles) which have a capacitative effect.

Furthermore, a lower bound frequency for an alternating current reference signal may be selected to control the remote electrical load (or preferably the energiser output circuitry) impedance placed on the opposite end of the line from the interfacing transformer employed. As preferably the energiser impedance makes up the majority of the impedance experienced by the reference signal when placed on the fence line, the reference signal frequency may be selected to ensure that this termination impedance is of a reasonable and easily measured magnitude.

Such a manageable terminating impedance will clearly indicate whether a short or open circuit has occurred between the interfacing transformer and the energiser.

In a further preferred embodiment, a reference signal frequency of between 100 Hz to 5 kHz may be employed. The selection of this particular frequency range will allow as high as possible reference signal frequency to be employed without necessarily coming close the resonant frequency of the fence line to be monitored.

Furthermore, the applicants have found that a reference signal frequency of between 1 kHz-2 kHz is also preferable in some instances where some common forms or constructions of electric fence energiser output circuits are applied at the terminating end of the fence line monitored.

The present invention may provide many potential advantages over the prior art.

A monitoring apparatus and method of using same may allow the condition of an electric fence line to be monitored without the need for the fence line to be energised by the high voltage electrical pulses or signals. This allows the condition of the fence line to be monitored even when the fence is turned off during hours

when authorised personnel are usually in the vicinity of the fence.

The present invention may allow the condition of an electric fence line to be monitored concurrent with the transmission of high voltage pulses or signals down the same electric fence line. The present invention may provide such a monitoring facility both concurrent with the operation of electric fence energiser and also when such an energiser is not used or turned off.

The use of a low voltage alternating current reference signal in preferred embodiments also allows authorised personnel to work in the vicinity of and potentially come into contact with the fence line, without health and safety issues.

The combination of preferably a high voltage insulated transformer used as an interface adapter and the provision of a low voltage alternating current reference signal protects the electrical components employed by the monitoring apparatus and also limits the voltage of the signals induced or placed onto the fence line.

Furthermore, the reference signal may provide minimal power consumption demands for the reference signal generator employed thereby providing a relatively efficient and low power consumption monitoring apparatus.

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: Figure 1 illustrates a block schematic diagram of a monitoring apparatus when interfaced with a fence line in accordance with a preferred embodiment of the present invention; and Figure 2 shows a block schematic diagram of components employed in the construction of a monitoring apparatus as configured in

accordance with a further embodiment of the present invention; and Figure 3a shows a block schematic diagram of components employed in construction of the detection system discussed with respect to figure 1; and Figure 3b shows a block schematic diagram of components employed in the fence isolation and protection system employed in the apparatus discussed with respect to figure 1; and Fiqure4a &4b show voltage versus time waveform plots for a translated signal in figure 3a as received by the detection system discussed in figure 2, and a rectified translated signal 3b.

BEST MODES FOR CARRYING OUT THE INVENTION Figure 1 shows a block schematic diagram of a monitoring apparatus when interfaced with a fence line in accordance with a preferred embodiment of the present invention. The components of the monitoring apparatus are shown within the dotted outline illustrated.

The monitoring apparatus consist of and incorporates a reference signal generator, showing this embodiment as a low voltage AC wave generator (1). The monitoring apparatus also includes an interface adapter, which is provided in this embodiment by a high voltage isolation transformer (2) which preferably includes protection components. The last major component employed in the monitoring apparatus is a detection system, shown in this embodiment as a detection circuit (3).

The wave generator (1) and detection circuit (3) are provided with direct electrical connections to the primary windings of the isolation transformer (2). Conversely

the secondary windings of the transformer (2) are connected to live (4) and ground (5) for an electric fence line. An electric fence energiser (6) is located at the opposite end of the line.

When the energiser (6) is operated, high voltage electrical pulses are transmitted.

However, the isolation transformer (2) isolates the wave form generator (1) and detection circuit (3) from these pulses and thereby from damage by these high voltage pulses.

Through its connection to the primary windings of the transformer (2) the wave form generator (1) generates a reference signal which is induced over the transformer onto the fence line. In the embodiment discussed with respect to figure 1, a 24 volt alternating current wave form is applied as the reference where this signal has a frequency of approximately 1-2 kHz. The induced reference signal is then modified by the characteristics or condition of the fence line and the electric fence energiser to subsequently produce a translated signal present on the fence line.

Significant changes in the electrical impedance experienced by the reference signal caused by for example, short circuits or open circuit (which in turn modify the connection of the majority of the impedance caused by the energiser (6)) will result in changes to the translated signal. This translated signal, due to its alternating current based nature, is induced back over the secondary to primary windings of the transformer and is available as an input to the detection circuit (3).

Figure 2 shows a block schematic diagram of components employed in the construction of a monitoring apparatus as configured in accordance with a further embodiment of the present invention.

In the embodiment shown with respect to figure 2 a monitoring apparatus (11) is

again provided. The apparatus is connected to a fence system (4,5) through a fence isolation and protection unit (2), again implemented through a high voltage isolation transformer.

In the embodiment illustrated with respect to figure 2, the majority of the signal processing and signal generation functions of the monitoring apparatus (11) are implemented through use of a microprocessor (17). The microprocessor (17) is used to generate an alternating current square wave signal which is subsequently supplied to a further sine wave filter wave monitor (18) for smoothing or modification into a sine wave signal. The filtered sign wave (destined to form the reference signal required) is then subsequently supplied to a gain control amplifier (19) which fine tunes the voltage amplitude of the signal to provide a consistent, reproducible reference signal. The microprocessor again controls the operation of the gain controlling amplifier (19) through the additional feedback loop shown.

The microprocessor (17) also receives a signal from signal measurement circuitry (13) for subsequent consideration and detection of any abnormal fence conditions.

If problems with the state of the fence are detected by the microprocessor (17) a series of light emitting diode indicators (20) may be lit by the microprocessor. In addition, control signals to other independent electrical equipment or components can be transmitted by the microprocessor through relay output connections (21).

Figure 3a shows a block schematic diagram of components employed in construction of the detection circuit discussed with respect to figure 1.

The detection circuit (3) includes an input stage which feeds into an operational amplifier (7). The amplifier boosts the voltage of the translated signal received to a level which can be easily managed and manipulated by the remaining components of the detection circuit (3).

Next the amplified signal is supplied to a peak detection system (8) which produces a DC electrical signal from the AC translated signal. This peak signal has a voltage proportional to the amplitude peaks of the source AC translated signal.

This peak signal is lastly supplied as an input to a pair of comparators (9 & 10).

The first comparator (9) tests the input voltage against an upper threshold voltage value. If the input voltage is higher than the upper threshold voltage, the output line of the comparator sends an alarm signal to a warning buzzer (not shown).

Conversely with the second comparator, the peak translated signal voltage is compared against a lower threshold voltage value and an alarm condition is indicated if the input voltage is below this lower threshold voltage.

Figure 3b shows a block schematic diagram of components employed in the fence isolation protection system discussed with respect to the monitoring apparatus of figure 1.

The isolation and protection system includes an insulated transformer (11) with one winding connected to the fence line to be monitored (not shown). The remaining winding of the transformer (11) is connected to a pair of damping resistances (12) and a current blocking diode (13). A pair of output terminals (14) are provided to link the isolation and protection system to other components of the monitoring apparatus which require protection from high voltage pulses transmitted along the fence line monitored.

The combination of the resistances (12) and current blocking diode (13) serve to damp out and dissipate the energy of pulses transferred across the transformer (11) and also provide a current blocking rectification facility through the diode (13).

Figure 4a & 4b show voltage versus time waveform plots for a translated signal, in figure 4a and a peak signal in figure 4b.

As can be seen from a comparison of figures 4a and 4b, the peak detection circuit employed in the detection circuit modifies the alternating current waveform of the original translated signal (shown in figure 4a) to a straight, flat DC voltage signal as shown with respect to figure 4b.

Figure 4b also shows the upper and lower threshold voltage values which indicate whether an alarm condition has been detected using the supplied translated signal.

A DC value in the middle or between these two voltage thresholds will indicate a normal or acceptable condition for the fence line monitored whereas a voltage outside of this accepted band will trigger the indication of 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.