NZ582600A

NZ582600A - Electric fence energiser with automatic control circuit capable of detecting human contact

Info

Publication number: NZ582600A
Application number: NZ582600A
Authority: NZ
Inventors: Valery Hamm
Original assignee: Lacme Holding
Priority date: 2007-06-22
Filing date: 2008-06-20
Publication date: 2012-05-25
Also published as: WO2009013412A3; FR2917940B1; WO2009013412A2; FR2917940A1

Abstract

Disclosed is an electric fence energiser including a measurement and control circuit (8) comprising: means for the periodic measurement of at least one electric parameter characteristic of the instantaneous impedance at the terminals of the energiser, using a sufficiently short period so that the measurement can be repeated multiple times during the pulse; comparison means for comparing the results of the measurement of the at least one parameter to reference values; and control means which can instantly alter the characteristics of the current pulse so that it does not pose a danger to people in the event of a deviation between the measurement results and the reference values, which deviation may indicate that a person has come into contact with the fence (6).

Description

<div class="application article clearfix" id="description"> IN THE MATTER OF NATIONAL PHASE PROCESSING IN : NEW ZEALAND OF THE INTERNATIONAL PATENT APPLICATION PCT/FR2008/000876 FILED ON : 20.06.2008 THE INVENTION OF : LACME HOLDING I, ~ Lou,j\ I ■ .4 6r I- T , a ptev>c/i- Cctu^ e subject of ,tJJ ,■/> do hereby declare that I am well acquainted with the English and French languages and that the accompanying translation is a translation made by me of the above International Patent Application. To the best of my knowledge and belief, this is a true translation. Dated this day of 20 A 0 The subjects of the present invention are an electric fence energizer and a method of controlling the energizer. 5 An electric fence is generally intended to keep animals in a field or to prevent the intrusion therein of undesired animals. It may also be intended for the protection or safekeeping of goods and/or people. 10 The energizer is a generator of very short electric pulses, transmitted periodically every few seconds or so to the destination of an electric fence. To increase the efficiency of energizers when they are 15 connected to very specific fences - that is, very long fences, heavily covered in vegetation along their entire length, and yet extremely well looked after to limit the impact of "series" losses - manufacturers have preferred to increase the output pulse energy to 20 the point of rendering it dangerous, and unfortunately there have been regrettable fatal accidents. Standards have fixed limiting values in relation to the characteristics of each pulse delivered by an 25 energizer. In Europe these standard limits are currently 20 A peak and 5 J on a scale of load impedances between 5 Q and 500 Q. These values may be considered as the smallest upper bound on acceptable pulses, that is, pulses transmitted at the start of a 30 fence considered through experience as unable to cause a lethal accident. These values can therefore also be considered as an upper bound on an acceptable maximum that is likely to pass through a human body in the worst case. As an upper bound on a maximum is not a 35 maximum, in the remainder of this document the acceptable maximum will be called the threshold Sm. Knowledge about the exact thresholds of lethal risk of short electric pulses is relatively vague. This is - 2 - because the risks to be taken into account are not limited solely to the problem of possible ventricular fibrillation, a fairly well-defined phenomenon, but also extend to other phenomena such as, for example, 5 momentary loss of consciousness accompanied by respiratory arrest, in some cases without an automatic return to normal. Hence, although in attempting to cover these risks today's standards impose limits in terms of peak amps and energy, it is possible that 10 other quantities will one day be taken into account. This was, for example, the case in the past with an additional limit in coulombs, which added to that on current and that on energy. This limit to 2.5 mC disappeared a little over 10 years ago, but might well 15 reappear in the future. Hence, in the remainder of this document the threshold Sm should not necessarily be considered as an energy in Joules or a peak current in amps, but can also be 20 considered to be any quantity at all, or an n-plet of quantities, characterizing an electric pulse which is not to be exceeded in the human body. In the same w^y, these quantities can describe not only the electric pulse characteristics but also those linked to its 25 duration. As will be observed, this preliminary observation on the subject of the threshold Sm is of no consequence to the nature of the invention. 30 Technical progress today allows the possibility to be glimpsed of exceeding the limiting values of 20 A peak and of 5 J over 5 to 500 ohms for an energizer conforming to the standards while guaranteeing that a 35 human body coming into contact with the fence never receives more than a maximum electric shock which is less than the threshold Sm. - 3 - Known energizers are able to detect a variation in impedance at their terminals caused, for example, by the contact of a human body with the electric fence. 5 There are also fence energizers able to deliver, for a predetermined delay, pulses that are not dangerous to the human being in the case of detecting a low impedance that might correspond to a human body coming into contact with the electric fence. When the 10 predetermined period expires, if the low impedance is still present, the energizer considers that it is not a human body (which would already have moved away) but another cause of low impedance, for example due to vegetation or branches being in contact with the 15 electric fence or a wire partly falling to the ground. In this case, these types of energizers, sometimes called "delayed effect energizers", or "intelligent energizers" or even "energizers with delayed compensation for the state of the fence", can then 20 increase the pulse characteristics so as in theory to maintain the guarding efficiency without this initially seeming to present a risk to personal safety. Such a control method is applied to the regular 25 measurement, at each cycle, of the impedance present at the energizer terminals. A first known solution consists in measuring this impedance at each pulse and in adjusting the 30 characteristics of the following pulse depending on the measurement. This solution may be acceptable if the characteristics of every pulse are always below the threshold Sm. It is no longer acceptable if it is envisaged that they should exceed this acceptable 35 threshold, since in this case a human body coming into contact with certain electric fences between two pulses might receive a dangerous pulse before the level is readjusted at the following pulse. - 4 - A second solution consists in using complex pulses consisting of a weak pulse, the characteristics of which are far below the threshold Sm, followed - for a very short time, less than 10 ms, imposed by the safety 5 standard for the admissible duration of an electric fence pulse - by one or more strong pulse (s), the characteristics of which may, possibly i.n combination with those of the weak pulse, exceed the threshold Sm. Thus at the start of each cycle of about a second the 10 weak pulse - most often, the beginning of it - allows the impedance at the energizer terminals to be measured. The very short time gap between the weak pulse and the strong pulse (or strong pulses) suffices to adjust the characteristics of the remaining strong 15 pulse to an inoffensive level if the arrival of a human body has been detected. However, the probability that a contact is dangerous, because undetected due to the arrival of a human body just after the moment of the weak pulse where the impedance is evaluated but before 20 the end of the complex pulse, is far from negligible, because it is approximately equal to the time between the weak pulse and the remaining strong pulse divided by the time between two consecutive complex pulses. For example, even if the time between the weak pulse and 25 the strong pulse is only 4 ms, the respective durations of the weak and strong pulses are considered negligible as a simple pulse typically lasts 100 to 300 ps, and the complete cycle between two complex pulses is around 1.2 s, the probability of a dangerous contact is about 30 0.004/1.2 = 0.0033. Although low, this probability is not acceptable when the life of a human being is at stake. The aim of the present invention is to propose an 35 electric fence energizer and a method of controlling the energizer which avoid at least some of the aforementioned drawbacks and which guarantee that a human body which is not in contact with the fence when a simple or complex periodic pulse starts, but which - 5 - comes into contact with the fence during the delivery of the pulse and in any event before the end of this, will not receive an electric shock above the threshold Sm, even if the fence is supplied by a powerful 5 energizer. An electric shock is here, as in the rest of this document, understood to mean the remainder of the electric pulse between the start of the human body's contact with the fence and the end of the present pulse. 10 To this end, the subject of the invention is an electric fence energizer comprising or able to work together with an internal or external measurement and control circuit, able to control periodically the 15 emission by said energizer of a simple or complex pulse to the fence, characterized in that said measurement and control circuit comprises: means of periodic measurement, with a sufficiently short period for the measurement to be 20 repeated several times during the pulse duration, of at least one electrical parameter directly or indirectly characteristic of the impedance momentarily present at the terminals of said energizer; - comparison means for comparing the results of 25 measurement of said at least one parameter with reference values; and - control means able, in the case of divergence between the measurement results and the reference values likely to correspond to a human body coming into 30 contact with the fence in the course of a simple or complex pulse, to modify instantly the characteristics of the present simple or complex pulse in order that the remaining portion of the pulse is not dangerous for the human body. 35 The energizer preferably comprises at least one energy storage capacitor and a transformer, the primary of which is connected to said at least one storage capacitor and the secondary of which is connected to - 6 - said electric fence, said measurement and control circuit being able to control periodically the discharge of said at least one storage capacitor into the primary of said transformer and consequently the 5 emission by the secondary of the transformer of said simple or complex pulse to the fence. According to one embodiment of the invention, said electrical parameter is the current at the terminals of 10 said energizer, the measurement and control circuit comprising a measurement input connected to a current transformer placed at the terminals of said energizer. According to another embodiment of the invention, said 15 electrical parameter is the derivative of the current at the terminals of said energizer, the measurement and control circuit comprising a measurement input connected to a current transformer placed at the terminals of said energizer. 20 According to another embodiment of the invention, said electrical parameter is the voltage at the terminals of said at least one storage capacitor, the measurement and control circuit comprising a measurement input 25 connected to a point common to the primary of the transformer and to said at least one storage capacitor. According to another embodiment of the invention, said electrical parameter is an n-plet, n being a positive 30 integer, comprising for example the voltage at the terminals of said at least one storage capacitor and/or the current in the secondary of the transformer and/or the derivative of the current in the secondary of the transformer. 35 Advantageously, said current transformer is placed between the terminals of said energizer and an earth connection of the electric fence. - 7 - In a variant, the current transformer is placed between the terminals of said energizer and a conductor of the electric fence not connected to earth. 5 According to an embodiment of the invention, the measurement period is predetermined by the manufacturer or by the user. According to an embodiment of the invention, the 10 measurement period is variable over the course of a pulse depending on electrical or temporal parameters such as the maximum pulse power, the degree of progress within the present pulse and the impedance present at the energizer terminals at the start of the pulse. 15 Advantageously, said reference values are the results of samples or the average of samples taken during one (or several) simple or complex pulse(s) preceding the present simple or complex pulse. 20 The subject of the invention is also a method of controlling an electric fence energizer, comprising or able to work together with an internal or external measurement and control circuit, able to control 25 periodically the emission of a simple or complex pulse to the fence, characterized in that the measurement and control circuit: - periodically measures, directly or indirectly and with a sufficiently short period for the 30 measurement to be repeated several times during the pulse duration, the impedance of the fence at the energizer output; - compares the value of the impedance measured with a reference value and estimates whether a possible 35 divergence is likely to correspond to a human body coming into contact with the fence; and - when a divergence likely to correspond to a human body coming into contact with the fence has been detected, the measurement and control circuit modifies - 8 - instantly the characteristics of the present simple or complex pulse in order that the remaining portion of the pulse is not dangerous for the human body. 5 Advantageously, as the energizer comprises at least one energy storage capacitor and a transformer, the primary of which is connected to said at least one storage capacitor and the secondary of which is connected to said electric fence, said method is characterized in 10 that to measure the momentary impedance of the fence at the energizer output, the measurement and control circuit measures at least one electrical parameter among the current or the voltage at the terminals of said at least one storage capacitor, the current or the 15 voltage at the secondary of the transformer and a first or second derivative of at least one of the preceding quantities. The period of measuring the impedance of the fence is 20 preferably between 1 jis and 1 ms. The period of measuring the impedance of the fence is preferably 10 ps. 25 According to one embodiment of the invention, modification of the present pulse characteristics is ensured by limiting the energy and/or the current of the remainder of the pulse being applied to the fence. 30 According to another embodiment of the invention, limitation of the energy and/or the current of the remainder of the pulse is ensured by limiting the energy and/or the current applied to the primary of the transformer. 35 According to another embodiment of the invention, the energy and/or the current applied to the primary of the transformer is limited by interrupting the discharge of said at least one storage capacitor. - 9 - According to another embodiment of the invention, limitation of the energy and/or the current applied to the primary of the transformer is ensured by shunting 5 the primary of the transformer. The invention will be better understood, and other aims, details, features and advantages thereof will become more clearly apparent in the course of the 10 following detailed explanatory description of several embodiments of the invention, provided as purely illustrative and non-limiting examples with reference to the appended schematic drawings. In these drawings: - Figure 1 is a simplified schematic view of an electric fence energizer according to a first embodiment of the invention; - Figure 2 is a graph showing two curves representing the output current of the energizer as a function of time, with and without contact with a human body respectively; - Figure 3 is a view similar to Figure 1 showing a second embodiment of the invention; and - Figure 4 is a view similar to Figure 1 showing a third embodiment of the invention. Figure 1 shows a fence energizer powered either from the mains supply or from a primary cell or a battery 30 (not shown) . The energizer comprises a capacitor 1 for storing energy, designed to be charged to a voltage of a few hundred volts (for example, 600 V) by means that are not shown. It is quite obvious that the number of storage capacitors is not limiting. 35 The energizer comprises a transformer 2, the primary 3 of which is connected, on the one hand, to a capacitor 1 and, on the other hand, to a thyristor 4. The secondary 5 of the transformer 2 is connected, on the 15 20 25 - 10 - one hand, to a wire of the electric fence 6 and, on the other hand, to an earth connection 7. In an alternative, the earth connection 7 may be a wire -often called "neutral" - according to a mode of 5 operation well known to a person skilled in the art without this changing the nature of the invention. It will be observed that in the case of an energizer comprising a transformer 2 the terminals of the 10 secondary 5 of the transformer 2 constitute the energizer terminals. The energizer comprises a measurement and control circuit 8 which generally comprises a programmable electronic circuit equipped with a memory, of the microcontroller type. The circuit 8 may be internal or external, that is, it may be integrated into the energizer (as shown in Figure 1) or integrated into another case (not shown) connected to the energizer. The circuit 8 is able to control and/or periodically deliver trigger pulses to the gate 9 of the thyristor 4. At each trigger pulse the thyristor 4 becomes conducting, which in a manner known to a person skilled in the art leads to the appearance of a high-voltage pulse in the wire of the fence 6. The energizer comprises a current transformer or sensor 14 positioned on the earth terminal of the secondary 5 of the output transformer 2. In a variant, the sensor 30 14 might also be positioned on the other terminal of the secondary 5. The sensor 14 can, for example, be a Hall effect sensor, a current transformer, a resistor, or something else. 35 The sensor 14 is connected at an input 15 of the circuit 8. At regular, possibly variable, intervals the circuit 8 samples the value of the current measured and transmitted by the sensor 14. If this periodicity is variable, it may, for example, result from a 15 20 25 - 11 - calculation by the circuit 8 as a function of diverse parameters such as, for example, the maximum pulse power capable of being delivered during the present pulse, and/or the degree of progress within the present 5 pulse, and/or the maximum portion of the pulse able to leave the energizer in the given interval of time, and/or the impedance present at the energizer terminals at the start of the pulse. In all cases the sampling period must be sufficiently short to allow several 10 measurements in the duration of one pulse. The sampling period is preferably of the order of 1 ]is to 1 ms, for example approximately equal to 10 ]as, but might be shorter or longer depending on the technical characteristics of the circuit 8. 15 Figure 2 shows a curve 16 (solid line) representing the general form of the current measured by the sensor 14 for a given impedance at the energizer terminals. At time t3 a human body comes into contact with the fence 20 6, which has the effect of lowering the impedance at the energizer terminals. The current measured by the sensor 14 then quickly shifts from the value II to the value 12, as represented by the curve 17 (dashed line). 25 During the pulse, at the moment of each sampling, the circuit 8 periodically compares the value of the measured current with a reference value stored in memory. When the circuit 8 detects a sudden variation in the value of the current, it deduces from this the 30 possibility of a human body having come into contact with the fence 6 and modifies the characteristics of the remainder of the present pulse downwards so as to control the electric shock. 35 In Figure 2, detection of the risk of the arrival of a human body during a present pulse has been illustrated using an increase in current from the value II to the value 12, but this risk can be detected in an identical way in the case of a drop in current (this case is - 12 - possible, for example, if a fence is suddenly shortened when opening a gate while the clumsiness of the operator simultaneously makes a wrong movement and through his momentum touches the fence). 5 Detection may be linked to exceeding the reference value by a certain percentage, the percentage, for example, perhaps being constant whatever the impedance considered present at the energizer terminals at the 10 start of the present pulse. As a variant, this percentage can be defined as a variable; for example, it may be lower when the initial impedance is lower. In the same way, when the sampling frequency is high, 15 it may be decided, in order to take account of the inevitable uncontrollable variations in measurements, not to respond as soon as the sudden variation is detected for the first time, but only after this variation has been confirmed by one or more 20 measurements at successive times, as soon as the cumulative duration remains such that the portion of the pulse that has flowed in the worst case into any human being coming into contact with the fence is less than a predetermined safety threshold. In other words, 25 in this case the variation is considered likely to correspond to a human body coming into contact with the fence 6 only when this variation is sufficiently extended in time. 30 The reference values may be stored in a data table, stored in the circuit 8, containing a reference value linked with each impedance/sampling time pair. This solution has the disadvantage, however, of not taking account of the variations that might exist between one 35 energizer and another (manufacturing tolerances, for example). In addition, it requires a significant memory size as it requires storing the complete pulse form for each impedance value. - 13 - As a variant, when the circuit 8 has determined the absence of any human body in contact with the fence 6 -for example, when the impedance has been observed to be stable during a large number of successive pulses - it 5 stores the value of the current measured by the sensor 14, then, at the following pulse, uses the value stored at the preceding pulse as a reference value to determine the possible presence or non-presence of a human body in contact with the fence 6. As a variant, 10 to eliminate the influence of random variations caused, for example, by the wind, which changes the amount of vegetation in contact with the fence 6, the circuit 8 may use the average of several preceding values as a reference value. 15 When the circuit 8 detects the possibility of a human body coming into contact with the fence 6 in the course of the pulse, it instantly modifies the characteristics of the remainder of the present pulse. Preferably, 20 taking account of the importance of responding quickly, the circuit 8 cancels most of the remainder of the present pulse such that this remainder remains, for example, strictly below Sm. Carrying out several impedance measurements during the pulse allows the risk 25 of accident to be reduced. This is because, according to the standard, a simple or complex pulse may last as long as 10 ms. As this duration is relatively long, periodic detection of the risk of the presence or non-presence of a human body in contact with the fence 30 during the pulse allows the problem to be solved of a human body coming into contact with the fence during a "long" complex pulse for example, or even just after the release, but before the end, of a particularly powerful "single" pulse. 35 Figure 3 shows a second embodiment of the invention in which the circuit 8 uses the voltage at the terminals of the capacitor 1 to detect the possible presence of a human body in contact with the fence 6. - 14 - In the second embodiment, the energizer comprises a resistor 19 if low value, for example a few ohms. The resistor 19 is connected in series with a thyristor 20, 5 the resistor 19 and the thyristor 20 together being connected in parallel to the capacitor 1. When the circuit 8 detects a human body coming into contact with the fence 6, it makes the thyristor 20 10 conducting by sending, via an output 21, a trigger pulse to the gate of the thyristor 20. This has the effect that the capacitor 1 suddenly discharges into the resistor 19, which ends the pulse quickly and without danger to the human body. It is obvious that a 15 similar system could be used in an energizer comprising a current sensor similar to the sensor 14 of the first embodiment. Figure 4 shows a third embodiment of the invention in 20 which the energizer comprises a current sensor 14 to . detect any human body coming into contact with the fence 6. In the absence of any possibility of contact of a human 25 body with the fence 6, an electronic switch 22 (for example, of the MOS power transistor, IGBT or other type) is permanently switched on by means of an output 23 of the circuit 8. 30 When the circuit 8 detects the possibility of a human body coming into contact with the fence 6 in the course of the pulse, it switches off the electronic switch 22 by means of its output 23, which has the effect of ending the pulse without danger to the human body. 35 The means necessary for controlling or absorbing the inductive energy in the transformer 2 are not shown in Figure 4. They are known to a person skilled in the art and are not part of the invention. It is obvious that a - 15 - switch similar to switch 22 could be used in an energizer similar to that of the second embodiment. To increase the reliability in detecting a human body 5 coming into contact with the fence 6, the circuit 8 may simultaneously use an input similar to the input 13 of the second embodiment to test the discharge of the capacitor 1 and an input similar to the input 15 of the first and third embodiments to receive information 10 delivered by a current sensor 14. Furthermore, other parameters characteristic of the impedance might be used in addition to or in place of those previously described (the current at the secondary 5 of the transformer 2 and the voltage at the terminals of the 15 capacitor 1. For example, a characteristic parameter may be the voltage at the secondary 5 of the transformer 2 or the current at the terminals of the capacitor 1. Furthermore, a parameter indirectly characterizing the impedance, for example a derivative 20 of a previously mentioned parameter-, may also be used. At the end of the pulse during which the circuit has detected the possibility of a human body coming into contact with the fence 6, the circuit 8 may modify the 25 characteristics of the following pulse. It then has time between two consecutive pulses, that is, about 1.2 s, which is more than enough. The following pulse will then be complete and without danger to the human body, if this still happens to be in contact therewith. 30 In one particular embodiment of the control method, the modification of the remainder of the present pulse is optimized so that the remainder is still as dissuasive as possible without presenting a danger, which 35 increases the guarding security when the contact detected is in fact contact by an animal. For example, supposing that the threshold Sm is only a quantity in Joules, as soon as the circuit 8 detects - 16 - too large a downward divergence in impedance it calculates a value S'm = SmRd/ (Rd~Rc) t where Rd is the equivalent resistance associated with the last pulse time for which an absence of risk of the presence of a 5 human body was determined, and Rc is the equivalent resistance associated with the first pulse time for which a risk of the presence of a human body was determined. It then instantly modifies the characteristics of the remainder of the present pulse 10 in order that the shock in the end comes as close as possible to the value S'm, without however ever exceeding it. Hence the energizers of the three embodiments described 15 reduce the probability of a dangerous contact to a value close to 0 by monitoring the possibility of a human body coming into contact with the fence throughout the entire duration of the pulse. 20 Although the invention has been described in relation to several particular embodiments, it is quite obvious that it is in no way limited thereto and that it comprises all the technical equivalents of the means described, along with their combinations if these fall 25 within the scope of the invention. - 17 - </div>

Claims

<div class="application article clearfix printTableText" id="claims"> CLAIMS

1. Electric fence energizer comprising or able to work together with an internal or external measurement and 5 control circuit (8), able to control periodically the emission by said energizer of a simple or complex pulse to the fence (6), characterized in that said measurement and control circuit (8) comprises: means of periodic measurement, with a 10 sufficiently short period for the measurement to be repeated several times during the pulse duration, of at least one electrical parameter (I, V) directly or indirectly characteristic of the impedance momentarily present at the terminals of said energizer; 15 - comparison means for comparing the results of measurement of said at least one parameter with reference values; and - control means able, in the case of divergence between the measurement results and the reference 20 values likely to correspond to a human body coming into contact with the fence (6) in the course of a simple or complex pulse, to modify instantly the characteristics of the present simple or complex pulse in order that the remaining portion of the pulse is not dangerous for 25 the human body.

2. Energizer according to Claim 1, characterized in that it comprises at least one energy storage capacitor (1) and a transformer (2), the primary (3) of which is 30 connected to said at least one storage capacitor (1) and the secondary (5) of which is connected to said electric fence (6) , said measurement and control circuit (8) being able to control periodically the discharge of said at least one storage capacitor (1) 35 into the primary (3) of said transformer (2) and consequently the emission by the secondary (5) of the transformer (2) of said simple or complex pulse to the fence (6). - 18 -

3. Energizer according to Claim 1, characterized in that said electrical parameter is the current at the terminals of said energizer, the measurement and control circuit (8) comprising a measurement input (15) 5 connected to a current transformer (14) placed at the terminals of said energizer.

4. Energizer according to Claim 1, characterized in that said electrical parameter is the derivative of the 10 current at the terminals of said energizer, the measurement and control circuit (8) comprising a measurement input connected to a current transformer placed at the terminals of said energizer. 15

5. Energizer according to Claim 2, characterized in that said electrical parameter is the voltage at the terminals of said at least one storage capacitor (1), the measurement and control circuit (8) comprising a measurement input (13) connected to a point common to 20 the primary (3) of the transformer (2) and to said at least one storage capacitor (1).

6. Energizer according to Claim 2, characterized in that said electrical parameter is an n-plet, n being a 25 positive integer, comprising for example the voltage at the terminals of said at least one storage capacitor and/or the current in the secondary of the transformer and/or the derivative of the current in the secondary of the transformer. 30

7. Energizer according to Claim 3, characterized in that said current transformer (14) is placed between the terminals of said energizer and an earth connection (7) of the electric fence (6). 35

8. Energizer according to Claim 3, characterized in that the current transformer (14) is placed between the terminals of said energizer and a conductor of the electric fence (6) not connected to earth. - 19 -

9. Energizer according to Claim 1, characterized in that the measurement period is predetermined by the manufacturer or by the user. 5

10. Energizer according to Claim 1, characterized in that the measurement period is variable over the course of a pulse depending on electrical or temporal parameters such as the maximum pulse power, the degree 10 of progress within the present pulse and the impedance present at the energizer terminals at the start of the pulse.

11. Energizer according to Claim 1, characterized in 15 that said reference values are the results of samples or the average of samples taken during one (or several) simple or complex pulse(s) preceding the present simple or complex pulse. 20

12. Method of controlling an electric fence energizer, comprising or able to work together with an internal or external measurement and control circuit (8), able to control periodically the emission of a simple or complex pulse to the fence (6), characterized in that 25 the measurement and control circuit (8): - periodically measures, directly or indirectly and with a sufficiently short period for the measurement to be repeated several times during the pulse duration, the impedance of the fence (6) at the 30 energizer output; - compares the value of the impedance measured with a reference value and estimates whether a possible divergence is likely to correspond to a human body coming into contact with the fence (6); and 35 - when a divergence likely to correspond to a human body coming into contact with the fence (6) has been detected, the measurement and control circuit (8) modifies instantly the characteristics of the present simple or complex pulse in order that the remaining - 20 - portion of the pulse is not dangerous for the human body.

13. Method according to Claim 12, the energizer 5 comprising at least one energy storage capacitor (1) and a transformer (2), the primary (3) of which is connected to said at least one storage capacitor (1) and the secondary (5) of which is connected to said electric fence (6), characterized in that to measure 10 the momentary impedance of the fence (6) at the energizer output, the measurement and control circuit (8) measures at least one electrical parameter among the current or the voltage at the terminals of said at least one storage capacitor (1) , the current or the 15 voltage at the secondary (5) of the transformer (2) and a first or second derivative of at least one of the preceding quantities.

14. Method according either of Claims 12 or 13, 20 characterized in that the period of measuring the impedance of the fence is between 1 ias and 1 ms.

15. Method according to Claim 14, characterized in that the period of measuring the impedance of the fence is 25 10 ]is.

16. Method according to Claim 12, characterized in that modification of the present pulse characteristics is ensured by limiting the energy and/or the current of 30 the remainder of the pulse being applied to the fence.

17. Method according to Claim 16 taken in combination with Claim 13, characterized in that limitation of the energy and/or the current of the remainder of the pulse 35 is ensured by limiting the energy and/or the current applied to the primary (3) of the transformer (2).

18. Method according to Claim 16 taken in combination with Claim 13, characterized in that limitation of the - 21 - energy and/or the current applied to the primary (3) of the transformer (2) is ensured by interrupting the discharge of said at least one storage capacitor (1). 5

19. Method according to Claim 16 taken in combination with Claim 13, characterized in that limitation of the energy and/or the current applied to the primary (3) of the transformer (2) is ensured by shunting the primary (3) of the transformer (2). </div>