BACKGROUND ART The electric fence industry is highly competitive. In this competitive market, the perception is the more powerful the energiser, the better the energiser. An energiser that has a greater shock effect, while still adhering to the regulations placed on the various electrical parameters associated with electric fences, are the most desirable.

Consequently, more powerful energisers are being produced.

A reason for more powerful energisers being more marketable, is that less spraying of or maintenance of the electric fence system is required. Often, a degradation of signal strength occurs due to environmental conditions.

Such environmental conditions include the earthing of the electric fence system by the conductive wires coming in contact with grass and weeds. Therefore a consumer must control the height of the weeds and grass surrounding an electric fence or along its length. This involves increased costs due to labour, sprays and so forth.

Similarly. the degradation of the conductive wire itself has a greater negative effect on the effectiveness of an electric fence system that has a lower power energiser as opposed to a high power energiser. A powerful energiser may still deliver an effective shock along the conductive length despite conductive degradation.

There is also a trend towards having large and longer fence systems in farms.

Therefore. a more powerful energiser is required to send an effective pulse along the entire system.

Electric fences are usually set up to enclose animals or prevent them from leaving or entering a particular area. Such animals include cows, bulls. sheep, deer and other animals. In the case of bulls, powerful energisers are required to give a sufficient shock given the size of the animal.

However, problems can arise. The problem generally arises when bulls fight. Because of their girth, bulls become extremely tired and exhausted after fighting with other bulls. They become so exhausted that it is possible for them to lie on an electric fence for a period of time. Bulls can also become entangled in the fence in some other way because of their size. For example, a bull may get trapped in a drain, caught in rails and so forth.

Their exhaustion is such that they are unable to remove themselves from the electric fence. This can lead to the bulls receiving multiple shocks from the fence, which can prove fatal.

The financial cost to the farmer when a bull is killed is substantial. Bulls are worth in order of hundreds of thousands of dollars, and are worth a great deal of money for stud applications.

It is extremely important therefore, to protect and ensure the safety of bulls, and other valuable animals which may become entangled and incapacitated.

Such accidents can also happen to other animals which may become lame or some other reason become stuck against an electric fence, which will led to multiple shocks which could prove fatal. For example, animals panicked by an event such as hot air ballons, noisy machinery and so forth.

Further, a high voltage pulse is preferable for physiological reasons as a high voltage pulse can deliver a shock of greater multitude through the body of an animal more effectively than a low voltage pulse.

Conductive material may also fall on the fence and create a conditional current drain on the energiser causing it to become overloaded. This can result in energiser damage, or result in a reduction in the effectiveness of the fence system.

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 an electric fence energiser including an energy storage device, the discharge of which provides the output of the energiser, a control unit that can control the output of the energiser, wherein the output of the energiser is a series of pulses, and a sensing means that can relay information to the control circuit regarding the detected electrical load on the output of the electrical fence energiser, characterised in that the energiser output is controlled by the control unit according to the rate of change of the electrical load detected by the sensing means.

The energy storage device fitted in most energisers is a capacitor, or a set of capacitors.

The output of most energisers is supplied by the discharging of one or more energy storage capacitors.

The charge and hence the voltage on the storage capacitor may be controlled by a number of means.

In a preferred embodiment, a control unit containing a controllable charging circuit may be placed somewhere between the charging circuit of the energiser and the capacitor. Furthermore, the controllable charging circuit may be switched on and off to control the charge reaching the capacitor as is desired.

In preferred embodiments, this controllable charging circuit may be a triac. However this should not be been to be limiting the scope of the present invention's manufacture or use and it should be appreciated that other charging circuiting devices such as thyristors, other SCRs, mechanical devices, optical charging circuits and so forth may be used.

In preferred embodiments, a microprocessor or micro-controller technology may be used in the control circuit.

Preferably, the controllable charging circuit may be connected to one of the ports on the microprocessor. When the microprocessor receives feedback from the sensing mechanism, which gives an indication of the load on the fence, the microprocessor may then calculate a value, in accordance with the predetermined parameters, or access and value from a memory means.

This value may be indicative of the voltage which should be stored on the energy storage capacitor that gives the desired output voltage on the fence line once the capacitor is discharged through the energiser transformer.

The microprocessor may then open or close the controllable charging circuit as appropriate to allow the energy storage capacitor to be charged to another appropriate value based on the load on the output of the transformer.

For example, the rate of change may involve sensing a number of values of load on the output of the energiser over a period of time using the sensing means. These values may be stored in the memory means of the microprocessor.

The sensing means, which provides an indication of the load, may be achieved in a variety of ways.

For example in one embodiment, current feedback may be used. A resistor of known value can be placed on the secondary side of the energiser output transformer. The voltage across this resistor can be measured, from which the current can be calculated and used to estimate the energiser load.

Alternatively, a resistor of known value may be placed on the primary side of the energiser circuit and the voltage measured across the resistor. The current can then be calculated and the effective impedance on the secondary side of the energiser can be calculated.

However. as the current tends to change when capacitive loads are placed on the circuit, current feedback has associated disadvantages.

In another embodiment, voltage feedback may be used. The energiser load may be estimated from the peak voltage at the secondary side of the transformer. For example the peak voltage on the secondary side can be measured while maintaining the isolation between the transformer primary and secondary through a capacitor divider network or a tertiary winding on the output transformer.

In another embodiment, a system of measuring the phase angle between the voltage and current waveforms may be used.

In a further embodiment, a method of measuring primary voltage overswing to deduce output load may be used.

In preferred embodiments the change in load, and the duration of the measurement period of the change in load. before the control circuit determines the necessity for a change to the charge stored on the output capacitor is necessary, will be adjustable by the user.

This will give the user the ability to determine at what level they wish to trade the probability of detection against the probability of false alarms.

It is envisaged that in some preferred embodiments where high value stock is concerned, the controller of the site may elect a low threshold in order to insure they are alerted to any alarm, although this may raise the likelihood of them receiving false alarms, whereas sites where low value stock are situated, the site controller may elect a higher threshold in order to reduce the number of potential false alarms.

The following is an example found by the applicant during brief testing: The output voltage from the energiser, typically drops in the region of 5-10% when a load is applied to the energiser output It was found that this drop is almost independent of the load applied to the energiser within the tested range of 1-500ohms.

The drop was also almost independent of the distance from the energiser that the load was applied within the tested range of 0-5 Km.

A good reference period for the output voltage was found to be a rolling average over the last 5-30 minutes.

If the reference period was set to be too long then a rapid downpour of rain on a fence. that was in contact with a significant amount of grass along its length, may induce a false alarm.

A minimum of three pulses. below the threshold set to detect an alarm condition. in

preferred embodiments will be used in order to allow for animals to make contact and then clear the fence in its normal operation.

In the case that a change in detected load is found or determined to relate to an animal falling on the fence. then the change in output may be made by way of reducing the charge on the capacitor or even stopping the pulses or reducing the frequency of the pulses.

This has the advantage of giving the animal time to recover without permanent or fatal damage occurring to the animal. After a period of time the usual operation of the energiser may start again to prompt the animal to move.

As another example. very small changes in the load on the output of the energiser over a long period of time, may be sensed by the sensing means. The predetermined parameters may be such that this may correspond to a degradation of the electric fence line, or wet grass growing against a fence, and so forth.

The output on the energiser may then be increased according to the level of degradation, which may be determined by the predetermined parameters. The intensity of the output may be increased to compensate for the degradation in the electric fence line.

In preferred embodiments, the present invention may be a stand-alone device that works in combination with existing energiser systems.

This has the advantage that an entire new system need not be purchased by the farmer. thus reducing their costs.

In other embodiments, the present invention may be incorporated into new energisers.

This has the advantage that any degradation may be overcome by the more powerful shock intensity. and the electric fence will therefore remain effective in such situations.

The advantage of the present invention also has implications with communication aspects of energisers.

For example, there may be a condition that forces the output of the energiser to change, and is hence sensed by the sensing means, and assessed by the microprocessor according to the predetermined parameters. This may then be identifie as a particular problem to a farmer. The farmer can then be alerted to this problem and see to it.

For example, a bull may fall on the fence after fighting and this may be detected by the present invention because the load changes by greater than 5%. for more than three consecutive pulses. The farmer may be alerted to this via communication systems.

The farmer may then see to the problem.

Alternatively, a degradation over a long period of time may be detected by the sensing means, and via the predetermined parameters be identified as signal degradation due to wet grass or a line fault. The farmer may alerted to this via communications means and then may go and remedy the problem.

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 shows a schematic diagram of the present invention ; Figure 2 shows a schematic diagram of the present invention fitted to an existing energiser system.

BEST MODES FOR CARRYING OUT THE INVENTION With reference to Figure 1 there is shown an electric fence energiser system according to the present invention. It includes an energy storage capacitor 1. a controllable

charging circuit 2, a control circuit 3, and a sensing means 4.

With reference to figure 2 the present invention is shown working in combination with an existing energiser system 8. In this configuration the present invention includes a control circuit 3 and a sensing means 4.

The existing electric fence energiser system 8 already contains an energy storage capacitor 1, and a controllable charging circuit 2.

The sensing means 4 can relay information to the control circuit 3 regarding a detected electrical load on the output 5 of the electric fence energiser. The output of the electric fence energiser is connected to an electric fence line 6.

In operation, the sensing means 4 may sense information regarding the load on the output 5 with is connected to the electric fence line 6.

The microprocessor incorporated in the control circuit 3 adjusts the controllable charging circuit such that the energy storage capacitor is charged to a level in accordance with the predetermined parameters, in relation to the load on the electric fence line 6 and consequently the output 5 of the electric fence energiser.

The sensing means may sense a slow gradual change in the load on the output which. in accordance with the predetermined parameters, may cause the energy storage capacitor to be charged to a different level.

Alternatively. a rapid change in the load over consecutive pulses may indicate a different event, and may result in the energy storage capacitor being charged by the controllable charging circuit to a different level in accordance with the predetermined parameters.

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 of the appended claims.