EP0374055B1 - Electric fence incorporating a monitoring device - Google Patents

Abstract

Power supply device for electric fences, intended for penning livestock or for avoiding human intrusions into an enclosure, consisting of a box connected to a main power supply source generating high-voltage pulses of more than one second spacing comprising an indicator of isolation of the electric fence line, characterised in that the box contains a system for digitising a characteristic electrical quantity and an isolation indicator consisting of a digital or bar-graph display which displays the degree of isolation on each pulse, the assembly consuming only energy provided directly or indirectly by the said main power supply, and not by an auxiliary power supply source. <IMAGE>

Description

Electric fences are well known for sending pulses of high voltage, at regular intervals, on a conducting wire surrounding or dividing a field where animals graze. It is also known that such electric fences can be used to avoid the intrusion of people into an enclosure.

The effectiveness of an electric fence decreases when grasses touch the wire; these herbs bypass the impulses that normally pass through the animal or the person coming into contact with the wire.

Users are looking for control means to check the condition of the fence, that is to say its isolation from the ground, and thus be reassured about the effectiveness of the fence.

A rudimentary method is to put a hand on the ground and touch the wire with a long grass that absorbs the electric shock.

It has already been proposed for example in French patent ^No. 2,566,919 energizers having minimum level detectors of the pulse delivered by the energizer below which an alarm or "bell" is triggered alerting the user on the need to intervene, and for example, to cut too many grasses touching the fence wire.

These detectors have the drawback of not allowing the evolution of the isolation of the fence to be followed, an evolution which is often slow and corresponds to the growth of vegetation.

When the alarm is triggered, it is necessary to intervene immediately, failing which the guarding of the livestock is no longer ensured.

It is much better to have a continuous indication, allowing daily monitoring of the degree of insulation of the fence as it degrades, and thus being able to choose the moment, or the appropriate day to intervene preventively, before that the situation has become catastrophic.

WO-A-82 00 936 describes a system comprising a continuous indication of the state of the fence. This system calculates the values corresponding to several consecutive pulses and makes it possible to follow the average insulation of the fence wire but does not make it possible to detect the relatively random phenomena which one meets when sparks fly, from time to time, along d 'an insulator whose material has degraded, or, when a branch swayed by the wind, causes more or less occasional ignitions.

These priming phenomena must be eliminated because on the one hand, they call into question the durability of the insulation of the wire, and on the other hand, they are the source of radio interference.

In order to be able to be fully informed of the state of the fence, it is necessary to know the electrical characteristics at each pulse.

A regular, but low, value of the indication corresponds to many grasses touching the fence wire; the decision to intervene to re-establish the isolation, by weeding all along the wire, is then taken by the user according to the level reached, after a slow descent of the indicator observed during the previous days.

An irregular value of the indication corresponds to a localized incident for which it is necessary to determine the precise origin to remedy it.

Indicators (digital voltmeters) consisting of a resistance voltage divider, associated with a detector were then proposed whose one end of the resistance point is earthed by a small earth rod while the other end is placed on the electrified wire. The detector associated with the resistance point then makes it possible to assess the voltage remaining on the fence wire.

These indicators then give information on each independent pulse, but nevertheless have several drawbacks.

They require more or less demanding maneuvers which put off the user. The latter then often gives up doing them at the expense of the efficiency of his electric fence;

They also require an independent power supply such as a battery which must be replaced regularly.

It is impossible to leave such a system connected between the fence wire and the ground permanently as this would cause rapid wear of the battery.

In addition, these indicators display a peak value of the repetitive voltage as it depends on the repetitiveness of the contact resistance of the stake with the ground and therefore on the manner in which the stake is driven. This peak voltage value also depends on the peak line voltage value reached for a very short time, on the order of a few microseconds.

This value is on the one hand not very repetitive and on the other hand not very representative of the main impulse, usually a few hundred microseconds, the only important one as regards the physiological effects felt by the animals.

The present invention seeks to propose an energizer which overcomes the various drawbacks of known devices.

To this end, the present invention describes an energizer comprising an insulation measurement system integrated into the enclosure of the electric fence and comprising no auxiliary energy source.

The energizer described is of the "capacitor discharge" type, but it can also be of the "network alternation injection" type.

A diagram making it possible to better describe the principle of the invention is represented by FIG. 1.

The capacitor C is charged by a power supply A connected to a main power source such as the mains, a battery or a battery. The capacitor C is discharged at regular intervals, greater than one second, by means of the switch 1 in the primary of the main transformer T.

The role of the transformer T is to raise the voltage of the pulse and to ensure, particularly in the case of a supply by the mains supply, the essential isolation between the energy source and the closing circuit.

• a- d'intégrer l'impulsion avec une constante de temps suffisante pour éliminer les pics de tension dont la durée est trop brève pour être significative au plan de la douleur ressentie par l'animal touchant le fil;
• b- de détecter la valeur crête de la tension ainsi intégrée et de la numériser;
• c- d'attaquer un cadran numérique qui affiche à chaque impulsion une valeur proportionnelle à la tension crête détectée.

A voltage divider R1-R2 is composed of several resistors put in series in order to avoid breakdowns due to the high voltage. The output voltage of the pulse, associated with a certain notion of duration of the pulse, determines the energy remaining on the line to give a painful discharge to the animal or to the man touching the wire. This energy decreases when the insulation of the fence wire from the earth is degraded by plants touching the wire or by defective insulators. The pulse, divided by the resistance bridge, is sent to a measurement system M which has the role:

• a- to integrate the pulse with a time constant sufficient to eliminate the voltage peaks whose duration is too short to be significant in terms of the pain felt by the animal touching the wire;
• b- to detect the peak value of the voltage thus integrated and to digitize it;
• c- to attack a digital dial which displays at each pulse a value proportional to the detected peak voltage.

The displayed value can range from 0 to 99 (or 99.9) and then indicates at any time a sort of percentage of the isolation of the fence.

The display can also be done using a bar graph, or a moving needle system; reading is then more intuitive.

The measurement module M is supplied by a system of rectifiers D, capacitors C1, C2 ... and resistors R3, R4 ..., all of these components being connected according to a well known rectifier / voltage stabilizer scheme; the assembly then forms a circuit which is connected on the one hand to the "earth" output of the fence, and on the other hand to a point K where an alternating or impulse or direct voltage is generated.

For energizers powered by a battery or a battery, the "earth" output of the fence can be connected to one of the terminals of the battery or the battery, and point K to the other terminal of the battery or stack.

For energizers supplied by the network, it is essential to galvanically isolate the "earth" + "fence" circuit from the primary circuit of the main transformer which is itself connected to the network. The point K cannot therefore be directly connected to the main supply.

• a- Le point K est alimenté par un transformateur T2 comme représenté sur la figure 2. Le primaire du transformateur T2 est relié au réseau alternatif ; le secondaire est connecté entre la sortie "terre" et ie point K. L'isolement entre le primaire et le secondaire de T2 doit être particulièrement soigné afin de garantir une complète séparation entre le réseau et le circuit "terre" + "clôture", ce dernier étant soumis à des impulsions à haute tension pouvant atteindre 10.000 volts.
• b- Le point K est relié à une sortie spéciale du secondaire du transformateur principal T suivant le schéma électrique de la figure 1. Le circuit M travaillant sous basse tension (quelques volts), on ne sélectionne que quelques tours entre la sortie "terre" de T et la sortie spéciale où est connecté K. Ces quelques tours permettent de recharger les condensateurs C1 et C2 à chaque décharge électrique, sans consommer beaucoup d'énergie. Un second avantage de cette méthode d'alimentation du module M est de ne nécessiter qu'un seul transformateur très fortement isolé : le transformateur principal T.

Isolation can be achieved in two different ways:

• a- The point K is supplied by a transformer T2 as shown in Figure 2. The primary of the transformer T2 is connected to the AC network; the secondary is connected between the "earth" output and point K. The isolation between the primary and secondary of T2 must be particularly careful in order to guarantee a complete separation between the network and the "earth" + "fence" circuit, the latter being subjected to high voltage pulses of up to 10,000 volts.
• b- The point K is connected to a special output of the secondary of the main transformer T according to the electrical diagram of figure 1. The circuit M working under low voltage (a few volts), one selects only a few turns between the output "earth" of T and the special output where K. is connected. These few turns allow the capacitors C1 and C2 to be recharged at each electrical discharge, without consuming much energy. A second advantage of this method of supplying the module M is that it requires only one very highly isolated transformer: the main transformer T.

FIG. 3 and FIG. 4 relate to a variant of the present invention in which the degree of insulation of the fence is estimated by a measurement made in the part connected to the primary of the main transformer.

Between the P and Q outputs of the transformer primary, a voltage divider bridge is connected, consisting of resistors or possibly capacitors. A voltage proportional to the voltage between P and Q appears between points R and Q. This proportional voltage can also be obtained on an intermediate output provided for this purpose during the winding of the transformer primary, or by an additional winding on the transformer T completely separate from primary and secondary.

, où Vp et Vq sont les tensions apparaissant aux bornes du primaire, h le rapport de proportionnalité du diviseur de tension choisi, et Vz la tension de la diode Zener.The Zener diode Z and a load resistance Rz of Z make it possible to obtain, between points S and Q, a voltage $\text{Vm = [h (Vp - Vq) - Vz]}$

, where Vp and Vq are the voltages appearing at the terminals of the primary, h the ratio of proportionality of the voltage divider chosen, and Vz the voltage of the Zener diode.

The solid line curve in Figure 4 represents the voltage h (Vp - Vq) when the electric fence wire is well insulated. The dashed curve in the same figure 4 represents the voltage h (Vp - Vq) when the fence wire is poorly insulated. These two curves are intersected by the straight line - in dotted lines - of the voltage of the Zener Vz diode. We note that the duration of the first half-wave during which h (Vp - Vq) exceeds Vz very largely depends on the degree of insulation of the electric fence wire: t1 is much smaller than t2. Measuring and displaying this duration is therefore a means of informing the user about the state of his electric fence.

The measurement of times t1 or t2 can advantageously be done by opening an electronic door when Vm - [h (Vp - Vq) - Vz] becomes positive and by closing this door when Vm goes back to zero; the door is then kept closed for a time of the order of 0.3 to 0.5 seconds so as not to take account of any rebounds of the signal. The measurement and display of the door opening time are then an indication of the degree of insulation of the electric fence wire.

The advantage of this measurement carried out in the primary circuit of the transformer is that the measuring block and the display, which are completely separated from the secondary circuit by the insulating barrier existing between the primary and the secondary of the transformer T, can be supplied by a conventional circuit of diodes, resistors and capacitors, itself connected directly to the AC supply.

It is also possible to use a transformer which may be of low insulation.

Another method of estimating the insulation of an electric fence is to measure the peak current flowing through it. the primary of the transformer T during the pulse; this peak current can be analyzed either by measuring the voltage it gives rise to across a low value resistor Rs, connected in series with the primary of T (Figure 5), or by measuring the voltage appearing at the terminals of the secondary of a small T3 annex transformer whose primary, of low inductance, is crossed by the current of the main discharge (figure 6). In the same way as the variant of the invention described above (Figures 3 and 4), the measurement and display part of the signal characteristic of the insulation of the fence wire is supplied by a circuit connected to the terminals of the AC network without the security be questioned.

Claims (13)

1. A supply device for electric fences, intended for penning livestock or preventing human intrusion into an enclosure, consisting of a housing connected to a main supply source generating high voltage pulses separated by more than one second having an insulation indicator for the electric fence line, characterised in that the housing contains a measuring system providing a numerical value of a characteristic electrical magnitude and the insulation indicator consists of a numerical or bar graph display which displays the degree of insulation at each pulse, the assembly consuming only energy supplied directly or indirectly by the main supply and not by an auxiliary supply source.
2. A device according to Claim 1, characterised in that the control circuit for the display measures a characteristic value of the discharge pulse and produces a numerical value thereof, after which there is effected a small time integration to eliminate therefrom spikes or oscillations of which the short duration renders them unimportant at a physiological level.
3. A device according to Claim 1 or 2, characterised in that the insulating measurement system of the fence measures the peak value of an electrical magnitude of the discharge.
4. A device according to Claim 1 or 2, characterised in that the insulating measurement system of the fence measures the duration during which the electrical discharge value remains greater than a certain determined value.
5. A device according to Claim 4, characterised in that the duration of the electrical value is only measured during the first oscillation of the discharge.
6. A device according to any one of Claims 1 to 5, characterised in that the measurement is made at a potential divider connected to the terminals of the electric fence.
7. A device according to any one of Claims 1 to 5, characterised in that the measurement is made at the terminals of an auxiliary winding wound on the main transformer.
8. A device according to any one of Claims 1 to 5, characterised in that the measurement is made at the terminals of the secondary winding of a measuring transformer, of which the low self-induction primary winding is connected in series with the primary winding of the main transformer.
9. A device according to any one of Claims 1 to 5, characterised in that the measurement is made at the terminals of a low value resistance connected in series with the primary winding of the main transformer.
10. A device according to any one of Claims 1 to 5, characterised in that the measurement is made by means of a potential divider comprising resistors and/or capacitors connected in parallel with the primary winding of the main transformer.
11. A device according to any one of Claims 1 to 10, characterised in that the supply to the treatment and display system is made through a portion of the secondary winding which recovers a small part of the discharge pulse energy and sends it into a recovery-stabilisation supply circuit, galvanically disconnected from the primary circuit of the main transformer.
12. A device according to any one of Claims 1 to 10, characterised in that the measurement and display system may be supplied, for electrification units connected to the alternating current distribution network, by a voltage step-down transformer connected to the network.
13. A device according to any one of Claims 1 to 10, characterised in that the measurement and display system may be supplied, for electrification units connected to an accumulator or to a battery, directly by the main supply.

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