GB2403856A

GB2403856A - Electric fence device

Info

Publication number: GB2403856A
Application number: GB0414780A
Authority: GB
Inventors: Wilhelm Weinreich; Heinrich Schmidt
Original assignee: Horizont Geraetewerk GmbH
Current assignee: Horizont Geraetewerk GmbH
Priority date: 2003-07-10
Filing date: 2004-07-01
Publication date: 2005-01-12
Anticipated expiration: 2024-07-01
Also published as: GB2403856B; FR2857554A1; FR2857554B1; GB0414780D0; DE10332267A1; DE10332267B4

Abstract

An electric fence device feeds pulses into an electric fence having a load impedance (RZ, CZ) which is reduced when the fence is touched by a person or an animal. In order to avoid injury there is provision that, when there is a high load impedance (RZ, CZ), the pulses have low energy, and after the load impedance (RZ, CZ) has been reduced, they remain unchanged for an adjustable delay time period, and in that, after this delay time period has expired, the energy of the pulses is increased significantly. Furthermore, an electric fence device is described which has the property of reliably preventing a hazard caused by excessively large amounts of pulse energy.

Description

Method for operating an electric fence device and electric fence device

The invention relates to a method for operating an electric fence device which feeds pulses in to an electric fence which is connected thereto and which has a load impedance which is reduced when touched by a person or an animal. The invention also relates to an electric fence device having a charge capacitor and a switch which is clocked by means of a timer and which discharges, in the form of pulses, the charge capacitor, charged via a transformer, to an electric fence connected to said charge capacitor on the secondary side, using a fence transformer.

Electric fence systems are used in agriculture and other applications for fencing in domesticated animals and also for keeping out wild animals. According to EN 60335-2-76, high-voltage pulses are fed in to the fence at intervals of approximately one second. These pulses have energy contents in joules, the energy being limited to 5 joules when there is a 500 ohm loading on the device. The 500 ohms is a measuring resistance which is intended to simulate the resistance of an animal's body and which also applies as the resistance of the body of a person.

Electric fences have specific parameters such as fence capacitance (nF), line resistances (ohm), leakage resistances (ohm) and earth resistances (ohm). These electrical variables load the electric fence device and influence the pulse data such as voltage level and pulse energy.

The load impedance, which can be calculated from the parameters, is used as the loading variable for the device.

A fence entirely without leakage due to undergrowth l - 2 - consumes virtually no energy. It is sufficient to allow a relatively weak pulse to run along the fence in order to reliably deter an animal which is in contact with the fence at any location. Empirical values here are approximately 0.2 to 0.5 joules with a high voltage,

for example 5000V.

Electric fences are generally freely accessible to walkers, children and even sick and old people. There must be no risk for the latter if they inadvertently or intentionally touch the fence.

A slight shock on touching a fence gives a warning so that the person, but of course also the animal, moves away and does not make any further attempt to pass through or over the fence. This is intended to be the normal and risk-free function of the electric fence.

If the fence is surrounded by high grass, bushes and the like, the pulse energy from the wire is diverted to the earth, in particular under wet or moist conditions.

If an animal touches the fence at the same time, there is no longer sufficient deterrent energy present and the electric fence can no longer carry out it protective function and loses its actual purpose. This can only be counteracted if the pulse energy is significantly increased from, for example, 0.5 joules to 5 joules.

Customary, mains-operated electric fences are therefore operated with approximately 2 to 5 joules of charge energy so that a reliable deterrent is ensured even when there is undergrowth or in the case of very long fences. In special cases even much larger amounts of pulse energy are also used.

However, amounts of pulse energy of this magnitude can lead to injury to people, in particular to children, which may even possibly be fatal. The safety limit of - 3

the specification cannot cover the possible risks

occurring in practice. Numerous serious accidents have occurred throughout the world.

Devices which output only small amounts of pulse energy to a fence without undergrowth and with a high leakage resistance and then immediately switch over to relatively large amounts of pulse energy if a low resistance is registered are also known. This system is also capable of producing critical situations if a person, for example, places his head between two wires, in which case the effective resistance may be less than 500 ohms, for example 200 ohms and the device immediately greatly increases the amount of pulse energy, and can thus also cause injury.

Against this background, the object of the present

invention has been to specify a method for operating a known electric fence device and a novel electric fence device, the method and the device reliably preventing the described hazard.

According to the method, the object is achieved in that, when there is a high load impedance, the pulses have low energy, and after the load impedance has been reduced, they remain unchanged for an adjustable delay time period, and in that after this delay time period has expired the energy of the pulses is increased significantly.

A time delay of, for example, 20 to 30 seconds is conceivable. The delay time period must be dimensioned in all cases in such a way that persons who come into contact with the fence can release themselves without difficulty and thus suffer no injury. After the delay time period has passed and the load impedance has then been reduced further, it is to be assumed that the reduction in the impedance is due to undergrowth or the like. The increase in the amount of pulse energy after - 4 - the time delay then comes fully into effect and ensures that the protective effect of the fence is then restored. From the moment at which the person comes into contact with the wires of the fence up until the end of the delay time period, only a fraction of the energy is converted so that there is no longer any risk. When there are changes in the load impedance, such as is the case where there is contact by a person or an animal, the automatic adaptation of the amount of pulse energy to the modified condition is not triggered. This is also not necessary for deterrent purposes since the fence is loaded only by the individual resistance and there is no additional leakage of energy as long as undergrowth does not contribute to the reduction in impedance. If the loading is maintained, there is, as a rule, undergrowth present next to the fence or there is a fault, for example due to the fact that the fence has a short- circuit. In this case, significantly larger amounts of pulse energy are required to maintain the high voltage and make available sufficient energy. Precisely this energy is made available after the delay time period.

Correspondingly, according to one preferred development of the method there is provision that when there are high load impedances only enough energy is fed in to the fence to ensure that the fence can reliably carry out its protective effect and cannot cause any injury to a person. This situation is preferably brought about if only approximately 0.5 joule per pulse is fed in to the fence.

After the expiry of the delay time period, the amount of pulse energy is increased to such an extent that sufficient energy for deterring animals is still available in parallel with the leakage of energy, for example due to undergrowth. This is advantageously the case, for example, if approximately 5 joules per pulse is fed in to the fence.

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In terms of device technology, the object is achieved by means of an electric fence device which has the features mentioned at the beginning and is embodied in such a way that when there is a high load impedance pulses having low energy are fed in to the fence, and when the load impedance is reduced, they remain unchanged for an adjustable time period, before pulses with a significantly larger amount of energy are fed in to the fence.

A sensor is preferably provided which senses the electric current or the voltage or the combination of the two after a discharge pulse, this information being evaluated in a downstream control part in such a way that the type and magnitude of the loading of the fence are determined, the clocked switch being disconnected as a function of the loading of the fence during the discharge process if the amount of pulse energy has reached a predefinable value. A delay part, which delays an increase in the amount of pulse energy if the load impedance of the electric fence is reduced by an adjustable delay time period, is connected between the control part and the clock pulse transmitter.

The delay part may, for example, be implemented by means of a microprocessor. This solution is relatively costly. It is more simple to use a counter which simply counts the delay time period. Other solutions for the delay part are possible.

The invention is explained in more detail by way of example in the single figure of the drawing using a basic circuit of the electric fence according to the invention.

The charging capacitor C1 is charged using a transformer (not illustrated) and using a diode 2 to a specific value, preferably the maximum value of the - 6 charge voltage from a voltage source (not illustrated).

A clocked switch 4, which obtains its through- connection pulses from a clock pulse transmitter (T) closes the primary- side circuit at chronologically even intervals, for example at intervals of 1 s, for example for 0.1 to 0.3 ms. During this short pulse period, a current flows from the charge capacitor C1 via the primary winding of the fence transformer 3 and via the switch 4. The fence transformer 3 steps up the voltage on the secondary side so that a high voltage pulse is produced which is fed in to the fence. The fence is a load impedance (four pole) composed of the parameters of the capacitance of the fence, the line resistance, the leakage resistance, the earth resistance and also the line inductance. It is represented as being formed from the ohmic resistance Rz and the capacitor Cz.

The sensor S determines, from the pulse current and pulse voltage, the load impedance which is ultimately the decisive load for the electric fence device. This load can vary within wide ranges. In the case of heavy undergrowth it is therefore 100 ohms, and when there is contact with animals it is approximately 500 ohms and in an undergrowth-free state it is from 20 kohm to Mohm. The load resistance which is determined by the sensor S is evaluated in the downstream control part St. The control part St then disconnects the clocked switch 4 via the timer T during the discharge process.

According to the invention, a delay element Vz is installed between the control part St and clock pulse transmitter T. When the load impedance changes from high to low values, the delay element Vz ensures that the instruction to increase the amount of pulse energy is implemented after a time delay. - 7 -

Claims

Patent Claims 1. Method for operating an electric fence device which feeds

pulses into an electric fence which is connected thereto and which has a load impedance (Rz, Cz) which is reduced when the fence is touched by a person or an animal, characterized in that, when there is a high load impedance (Rz, Cz), the pulses have low energy, and after the load impedance (Rz, Cz) has been reduced, they remain unchanged for an adjustable delay time period, and in that, after this delay time period has expired, the energy of the pulses is increased significantly.
2. Method according to Claim 1, characterized in that, when there are high load impedances (Rz, Cz), only enough energy is fed in to the fence to ensure that the fence can reliably carry out its protective effect and cannot cause any injury whatsoever to a person.
3. Method according to Claim 2, characterized in that approximately 0.5 joule per pulse is fed in to the fence.
4. Method according to one of Claims 1 to 3, characterized in that, after the expiry of the delay time period, the amount of pulse energy is increased to such an extent that sufficient energy for deterring animals is still available in parallel with the leakage of energy as a result of any undergrowth which is present.
5. Method according to Claim 4, characterized in that approximately 5 joules per pulse is fed in.
6. Electric fence device having a charge capacitor (C1) and a switch (4) which is clocked by means of a timer (T) and which discharges, in the form of pulses, the charge capacitor (C1), charged via a transformer, - 8 - to an electric fence connected to said charge capacitor (C1) on the secondary side, using a fence transformer (3), said electric fence having a load impedance (Rz, Cz) which is reduced when the fence is touched by a person or an animal, characterized in that, when there is a high load impedance (Rz, Cz), pulses having low energy are fed in to the fence, and when the load impedance is reduced, they remain unchanged for an adjustable delay time period, before pulses with a significantly larger amount of energy are fed in to the fence.
7. Electric fence device according to Claim 6, characterized in that a sensor (S) is provided which senses the electric current or the voltage or the combination of the two after a discharge pulse, this information being evaluated in a downstream control part (St) in such a way that the type and magnitude of the loading of the fence are determined, the clocked switch (4) being disconnected as a function of the loading of the fence during the discharge process if the amount of pulse energy has reached a predefinable value, and in that a delay part (Vz), which delays an increase in the amount of pulse energy if the load impedance of the electric fence is reduced by the delay time period, is connected between the control part (St) and the clock pulse transmitter (T).
8. A method for operating an electric fence or an electric fence device, substantially as hereinbefore described with reference to or as illustrated in the drawing.
9. An electric fence or an electric fence device, substantially as hereinbefore described with reference to or as illustrated in the drawing.