Patent ID: 12253643

DETAILED DESCRIPTION OF AN EMBODIMENT

A system1for detecting a target object, and in particular an item comprising a ferromagnetic material of large volume such as an assault rifle, said system comprising:at least one first and a second detector10,20together forming a gate,at least one processing unit6andat least one communication interface7.

Each detector10,20comprises at least one magnetic sensor5. The term “magnetic” (or magnetostatic) is here understood to mean a passive sensor configured to detect a magnetic field that naturally surrounds objects containing iron or any ferromagnetic component, as opposed for example to an induction coil.

More precisely, the first detector10comprises at least one first magnetic sensor5, preferably at least two, for example three first magnetic sensors5, whereas the second detector20comprises at least a second magnetic sensor5. Preferably the second detector20and the first detector10each comprise as many sensors5.

Each magnetic sensor5is configured to detect a magnetic field and generate a signal representative of an intensity of the magnetic field thus detected. In an embodiment, the signal is a voltage, the value of which is proportional to the intensity of the magnetic field detected.

In an embodiment, each magnetic sensor5is configured to detect an intensity of a magnetic field along three orthogonal axes.

Each detector10,20further includes a post3, configured to be placed on a ground surface, for example via a base4. Preferably, one height of the post3is substantially equal to the average height of a person2, for example in the order of 1.70 m to 2.0 m.

The assembly formed by the post3and its base4is portable, i.e. it is not definitively anchored in the ground and can be transported by an operator. Where applicable, each detector10,20can be equipped with a handle in order to facilitate its transportation. The handle can in particular be attached to the base4.

The magnetic sensors5are distributed over the height of the post3in order to ensure the detection of target objects between the feet and the head of the persons2inspected. For example, each post3can be equipped with three magnetic sensors5, distributed between the base4and the free end of the post3.

Finally, within one and the same detection system1, the magnetic sensors of the detectors10,20are positioned pairwise at one and the same height so as to form pairs of sensors5facing one another.

The system1further comprises at least one processing unit6configured to receive the signals representative of an intensity of a magnetic field generated by the first magnetic sensor5and/or the second magnetic sensor5. The processing unit6then determines a corrected value of the signals generated by the magnetic sensors5of the first and second detectors10,20by applying an attenuation coefficient to the signals generated by the magnetic sensor or sensors5during the step S1 and, when said corrected value is greater than a predetermined threshold value, sends instructions to emit an alarm.

In an embodiment, the processing unit6computes an average value of the signals generated by the magnetic sensors5of the first and second detectors10,20and then applies the correction step to this average value. Alternatively, the processing unit6can first determine the corrected value of these signals then compute the average value of these corrected values.

The processing unit6can determine an arithmetic mean value of the signals, which corresponds to the sum of the values of the signals divided by the number of signals, or in a variant a geometric mean value of the signals, which corresponds to the square root of the product of the signals.

In an embodiment, the processing unit6can be incorporated into one from among the first detector10and the second detector20. Preferably, each detector10,20comprises an integrated processing unit6. The term “integrated” should be understood to mean that the processing unit6is part of the detector10,20and is not a separate component to which the system1is connected.

In this embodiment, the processing unit6can for example be attached to the post3of the associated detector, or in a variant its base4.

In a variant of this embodiment, the processing unit6can be placed at a distance away from the first and the second detector10,20. The detectors10,20then communicate to it the signals generated by their magnetic sensors5for the purpose of processing the signals by way of their communication interface7.

In an embodiment, the processing unit6can comprise:an analog-to-digital converter A/D, configured to convert an analog (voltage) signal generated by a magnetic sensor5into a digital signala Digital Signal Processor DSP, configured to produce the digital signal thus converted anda System Management Microcomputer SMM, configured to receive the digital signal produced by the DSP and compare it to the predetermined threshold value.

The SMM is connected to at least one emitter8configured to generate an alarm signal, for example an acoustic emitter8configured to generate an acoustic signal and/or a light configured to generate an optical signal (LED, flashing light etc.) The emitter8can be contained in the detector10,20or in a variant be worn by an operator (earpiece etc.) in which case the processing unit6sends the instructions to generate an alarm to the remote emitter8by way of the communication interface7of the corresponding detector10,20.

The SMM is moreover connected to an asynchronous interface UART in order to allow the connection of the processing unit6to a computer (or equivalent) to permit various actions including control of the detection program, diagnostics on one or more detectors, loading of updates etc.

Finally, the SMM is connected to a Human Machine Interface HMI.

Each detector10,20of the detection system1further comprises a communication interface7configured to allow one of the detectors10,20of the system1to communicate with another of the detectors20,10of the system1and transmit to it the signal generated by its magnetic sensor or sensors5. For each detector10,20, the communication interface7can be connected either to the DSP (as illustrated inFIG.1) of the processing unit6of this detector10,20, or to its SMM and to its alarm emitters8.

The communication interface7preferably comprises a wireless interface to facilitate the installation of the detection system1, for example an interface of Wi-Fi or Bluetooth type, by optical, radio, infra-red or else inductive communication, etc. In a variant, the communication interface7can be wired.

Where applicable, the detection system1can comprise a larger number of detectors in order to form a set of gates, each gate being formed by two adjacent detectors. Preferably, the detectors of one detection system1are substantially identical pairwise.

For example, the detection system1can include a third detector30comprising at least one third magnetic sensor5configured to detect a magnetic field and generate a signal representative of an intensity of the magnetic field thus detected.

In a similar way as the first and the second detectors10,20, the third detector30can include a post3attached to a base4and equipped with the third magnetic sensor or sensors5as well as a communication interface7and where applicable a processing unit6.

In order to form several gates, the invention proposes to place side-by-side the first detector10, the second detector20and the third detector30so as to form two gates. More precisely, the first gate is formed by the first detector10and the second detector20, whereas the second gate is formed by the second detector20and the third detector30. In the system, one same detector (here, the second detector20) is therefore used for the forming of two separate gates, which makes it possible to significantly reduce the bulk of the detection system1by comparison, for example, with the system proposed in the document WO 2017/141022. The system is furthermore easier to install.

As will be seen below, such a configuration is allowed by the fact that the processing unit6of the second detector20, which is located between the first detector10and the second detector20, can be configured both to process the signals generated by the magnetic sensor or sensors5of the third detector30and to communicate with the first detector10, so that the detection system1is capable of determining the gate within which a target object has been detected, even though the magnetic sensors5carry out a scalar and not a vectorial detection.

More precisely, the processing unit6of the second detector20is configured to:(i) compute a corrected value (where applicable averaged) or an average value of the signals generated by the second and third magnetic sensors5and,(ii) when said computed value is greater than the predetermined threshold value, transmitting to the processing unit6of the first detector10via the communication interface7a signal representative of an intensity of a magnetic field detected by the second magnetic sensor or sensors5as well as the computed value.

Of course, an operator can also use four detectors in accordance with the invention to form two gates, the sharing of the second detector20not being obligatory for the detection of target objects.

Each detector10,20can further include identifying means and a memory in order to allow association and communication with the other detectors of the detection system1as well as the implementation of the detection method S. For example, to each detector10,20,30can be assigned an address, which can be set when the detector10,20,30are manufactured or programmed when the detectors10,20,30forming the detection system1are paired. In an embodiment, the address of each detector10,20,30is fixed, i.e. non-modifiable, in order to limit errors of manipulation of the detection system1and to facilitate after-sales service.

An example of an address can comprise a character chain that can in particular be formed from a given number of hexadecimal pairs, for example eight.

When the detectors10,20,30of the detection system1are paired, the address of the detectors with which a given detector forms a gate is stored in the memory of said given detector. For example, in the case of a detection system1comprising the first10, the second20and the third30detector, at the time of parameterization of the detection system1:the address of the second detector20is stored in the memory of the third detector30the address of the first and third detectors30is stored in the memory of the second detector20at the time of parameterization of the detection system1andthe address of the second detector20is stored in the memory of the first detector10.

An example of a detection method S using a detection system1in accordance with the invention and comprising two detectors10,20will now be described.

In order to facilitate the reading of the description, the detection system1comprises a first detector10and a second detector20including two first magnetic sensors5and two second magnetic sensors5respectively. The first and second magnetic sensors5form two pairs of magnetic sensors5, each pair comprising a first sensor5and a second sensor5. Preferably, a pair comprises a first magnetic sensor5and a second magnetic sensor5each placed near a free end of the post3of the first detector10and of the second detector20, whereas the other pair comprises a first magnetic sensor5and a second magnetic sensor5each placed near their base4.

Both detectors are identical and each comprise a processing unit6and a communication interface7.

Of course, the invention applies mutatis mutandis in the case where the detectors comprise a different number of magnetic sensors5. In particular, the detectors could comprise only a single magnetic sensor5, or more than two magnetic sensors5(for example three magnetic sensors5). In addition, the second detector20could comprise no processing unit6, or in a variant the processing unit6could be placed at a distance from the detectors instead of being housed in the first detector10.

During a preliminary step, the first and second detector10,20are paired to associate them and configured so as to assign to each a function in the detection method S. For example, the first detector10can be configured as the master detector whereas the second detector20is configured as the slave detector. The “master detector” of a given gate is understood to mean the detector of which the processing unit6is configured to compute the corrected value and/or the average value of the signal, whereas the term slave detector should be understood to mean the other detector of said given gate.

During a first step S1, at least one from among the first and second magnetic sensors5generates a signal representative of an intensity of a magnetic field.

In practice, when a magnetic field is detected by one of the magnetic sensors5of the detection system1, all the magnetic sensors5of said system generate a signal representative of an intensity of the magnetic field detected, only the power of the signal of each sensor5being different.

The signals generated by the first and second magnetic sensors5are transmitted to the processing unit6, where applicable by way of the communication interfaces7of the first detector10and/or of the second detector20. In our example, the first detector10being the master and comprising the processing unit6, the signals of the second magnetic sensors5are transmitted to the first detector10by the communication interface7of the second detector20, whereas the signals of the first magnetic sensors5may be transmitted directly thereto by the first magnetic sensors5.

During a step S3, the processing unit computes a corrected value of the signals generated by each of the magnetic sensors5by applying an attenuation coefficient to said signals. Here, the processing unit6therefore computes a first corrected value corresponding to a first of the pairs of first and second magnetic sensors5, and a second corrected value corresponding to the second of the pairs.

This so-called correction step S3 thus makes it possible to attenuate the signals generated by the magnetic sensors5of the detection system1by applying a correction coefficient to the signals depending on the value of these signals. More precisely, the purpose of the correction is to attenuate the signal when the target object is near one of the detectors10,20, where the sensitivity is greater, in order to reduce its weight in the detection.

To do this, during the sub-steps S31 and S32, for each pair of magnetic sensors5, the processing unit6determines the maximum value and the minimum value from among the signals generated by the first magnetic sensor5and the second magnetic sensor5at a given time.

During a third sub-step S33, the processing unit6computes a ratio of the maximum value to the minimum value thus determined, then, during a fourth sub-step S34, compares the ratio with determined thresholds and deduces therefrom the value of the attenuation coefficient to be applied to the value of the signals.

For example, the processing unit6can in particular compare the ratio with a first threshold and with a second threshold, the second threshold being greater than the first threshold, and deduce the attenuation coefficient from it.

Thus, the attenuation coefficient can be equal to:a first value when the ratio is less than the first threshold,a second value less than the first value when the ratio is greater than the second threshold anda value between the first value and the second value when the ratio is between the first threshold and the second threshold. In particular, the attenuation coefficient can be a linear function depending on the ratio when said ratio is between the first threshold and the second threshold.

The use of the ratio between the maximum value and the minimum value makes it possible to determine if the target object that generates a magnetic field or disrupts the Earth's electromagnetic field is placed near one of the detectors. In this case, the value of the ratio is greater than the second threshold and the attenuation coefficient that is applied is equal to the second value, which is less than the first value. Contrariwise, when the target object is centered between the two detectors, the sensitivity of the gate in this zone is lower. This manifests as a ratio of the maximum value to the minimum value which is also lower. The attenuation coefficient can therefore be higher and the resulting attenuation coefficient lower.

A relative virtual uniformity between the two detectors is thus obtained.

By way of non-limiting example, the first threshold can be equal to 30, the second threshold can be equal to 60, the first value can be equal to 1, the second value can be equal to 0.1 and the attenuation coefficient can be defined by the following function when the ratio is between the first threshold and the second threshold:
−0.03*R+1.9
where R is the value of the ratio.

In other words, the attenuation coefficient can be equal to 1 when the ratio is less than 30, 0.1 when the ratio is greater than 60, and 0.03*R+1.9 when the ratio is between 30 and 60.

In a variant embodiment, instead of computing a corrected value of the signals of each pair of magnetic sensors5, the processing unit6of the master detector can compute an average value of the signals generated by each pair of magnetic sensors5(step S2). Here, the processing unit6therefore computes a first average value corresponding to a first of the pairs of first and second magnetic sensors5, and a second average value corresponding to the second of the pairs.

Of course, when the detectors each only comprise a single sensor5, the processing unit6only computes a single average value in the step S2 corresponding to the average value of the signals of these two magnetic sensors5.

As indicated above, the processing unit6can compute an arithmetic mean value of the signals or, in a variant, a geometric mean value.

In another variant embodiment, the processing unit6computes an average value of the signals for each pair of magnetic sensors5(step S2) and implements a step of correcting said signals (step S3).

To do so, after computing the average of the signals of each pair of magnetic sensors5(step S2), the processing unit6can apply an attenuation coefficient to the average values thus computed (step S3).

Alternatively, the processing unit6can first apply the attenuation coefficient to the signals of each pair of magnetic sensors5(step S3) then compute an average of the corrected signals of each pair of magnetic sensors5(step S2, applied to the corrected signals and not to the signals generated by the magnetic sensors5).

The attenuation coefficient can be identical to that which has been previously described (equal to the first value, the second value or a function of the ratio, according to the value of the ratio).

During a fifth step S5, the processing unit6compares the computed value with a predetermined threshold value.

The computed value used by the processing unit6during the fifth step S5 can be either the corrected value of the signals generated by the pairs of magnetic sensors5and obtained in the step S3, or the value corrected and averaged by applying an attenuation coefficient by implementing the step S2. When the corrected value, where applicable the corrected and averaged value, is greater than the predetermined threshold value, during a sixth step S6, the processing unit6sends instructions to emit an alarm (optical, sonic etc.) to at least one of the emitters8. Preferably, the processing unit6sends instructions to emit an alarm to the emitters8of the first detector10and the second detector20(via the communication interfaces7), such that one or more alarms are emitted on both sides of the gate. In a variant, only the emitter or emitters8of the one of the detectors10,20can receive the emitting instructions of the processing unit6.

Alternatively, when the processing unit6determines only a corrected value of the signals, without taking the average thereof, it is the sum of the corrected values of the signals (and not their average) which is compared during the step S5 with the predetermined threshold value. Of course, the signals generated by the sensors5can first be summed before the correction step S3 is applied to them.

Alternatively, instead of computing the sum of the corrected values of the signals, the processing unit6can determine the maximum value of the corrected signals and compare, during the step S5, the maximum value thus determined with the threshold value. In a similar way to that described previously, it is possible to first determine the maximum value of the signals generated by the sensors5then apply to this maximum value the correction step S3.

In this alternative, the processing unit6compares the sum of the corrected values (or the corrected maximum value respectively) of the signals of one and the same pair of magnetic sensors5with the predetermined threshold value. When this sum (or this corrected maximum value respectively) is greater than the predetermined threshold value, during the sixth step S6, the processing unit6sends instructions to emit an alarm (optical, audible etc.) to the at least one of the emitters8. As indicated previously, the processing unit6can send instructions to emit an alarm to the emitters8of the first detector10and/or the second detector20.

FIGS.8a,8band8cillustrate the intensity of the measured signal for four detection systems as a function of the distance with respect to the detector(s).

FIG.8aillustrates the case of a detection system in accordance with the prior art comprising two detectors separated by a distance of 130 cm. In this figure, the intensity represented corresponds to the maximum value of the signals generated by the sensors of the two detectors.

FIG.8billustrates the case of a detection system1in accordance with an embodiment of the invention comprising two detectors separated by a distance of 130 cm and comprising a processing unit. In this figure, the intensity represented corresponds to the average value of the signals generated by the sensors of the two detectors.

FIG.8cillustrates the case of a detection system1in accordance with an embodiment of the invention comprising two detectors separated by a distance of 130 cm and comprising a processing unit. In this figure, the intensity represented corresponds to the corrected average value of the signals generated by the sensors of the two detectors.

It is clearly apparent from this figure that the computing of the average value and, where applicable, the application of the attenuation coefficients during the step of correcting the average value, make it possible to uniformize the intensity of the signal between the two detectors of the detection system, by comparison with the simple determination of the maximum values of the signals (FIG.8a).

EXAMPLE

The table below is a comparative example of detection of one same target object by three configurations of detection system, namely (i) a detection system1comprising only a single detector, (ii) a detection system1in accordance with a first embodiment of the invention and comprising two detectors spaced apart by 130 cm with computation of the average value of the signals and (iii) a detection system1in accordance with a second embodiment of the invention and comprising two detectors spaced apart by 130 cm with computation of the average value of the signals and correction of said average value to determine if an alarm must be triggered.

In this example, the sensitivity SE of the three configurations of detection system has been set to 85% (equivalent to 1400 mV). In other words, the sensitivity has been set such that the predetermined threshold value is equal to 1400 mV. The systems have been parametrized such that at this sensitivity, the passing of a sphere of 75 mm in diameter at a height of one meter from the ground does not generate any alarm when it passes at 65 cm from the single detector (first configuration (i)) or in the middle of the two detectors (second and third configuration (ii) (iii)). In other words, the diameter of 75 mm is a limit diameter of detection by the tested systems. Specifically, the disruption of the electromagnetic field of an iron sphere of 75 mm in diameter substantially corresponds to the disruption generated by the presence of an assault rifle of AK47 type at the center of the gate.

Limit diameterLimit diameter(iii) System with[mm]two detectorsDistanceLimit(ii) System withwith computationbetween thediametertwo detectorsof the averagesphere and one[mm]with computationvalue andof the detectors(i) Singleof the averagecorrection of the[cm]detectorvalueaverage value101118351518235020233060253035643035406935405075404555644550606450606262556464646069696965757575

In this table, “limit diameter [mm]” corresponds to the minimum diameter in millimeters from which the detection system1tested emits an alarm signal.

The tests show that, in the case where the detection system1comprises two detectors forming a gate (configurations (ii) and (iii)) and the processing unit6computes the average value of the signals generated by the magnetic sensors5of these detectors, it is capable of discriminating target objects with a magnetic field equivalent to that of an iron sphere of approximately 62 mm from objects of smaller size such as smartphones, even if the target object is 50 cm away from one of the detectors (which, in practice, is already quite far from the center of the passage, the detectors being spaced apart by 130 cm during this test).

In the case where the processing unit6of the detection system1further applies a correction step S2 to the average value of the signals (configuration (iii)), the detection system1is further capable of distinguishing target objects with a magnetic field equivalent to that of an iron sphere of approximately 64 mm, even if the target object is 25 cm away from one of the detectors (i.e. very close to it, since the detectors are spaced 130 cm apart during this test).

The detection systems in accordance with the invention (configurations (ii) and (iii)) are therefore capable of discriminating objects of small size, even if these comprise magnetic components (such as smartphones), from target objects of large volume such as assault rifles, even if the passing of the inspected person2is not centered between the detectors.

The invention also applies to the case where the detection system1comprises a number of detectors greater than or equal to three so as to form a plurality of gates and where two adjacent gates share one and the same detector. An example of a method for detecting a target object using such a detection system1will now be described.

In order to facilitate the reading of this embodiment, the detection system1comprises three detectors each including two magnetic sensors5(FIG.3). In other words, the detection system1includes a first, a second and a third detector10,20,30, including two first, two second and two third magnetic sensors5respectively. The second detector20forms a first gate with the first detector10and a second gate with the third detector30. The second detector20is therefore located between the first detector10and the third detector30.

The three detectors are identical and therefore each comprise a processing unit6and a communication interface7. Of course, the processing unit6could in a variant be placed at a distance from the detectors and not be incorporated into the detectors. In this case, the signals generated by the magnetic sensors5of a given detector are transmitted to the remote processing unit6by way of the communication interfaces7of the detectors so that it applies the detection algorithm to them and then transmits any instructions to generate an alarm to the emitters8of the detectors, via their detectors, via their respective communication interfaces7.

Of course, the invention applies mutatis mutandis in the case where the system only comprises two detectors together forming a single gate or a greater number of detectors (for example n detectors, n being an integer number) together forming n−1 gates. The detectors could further only comprise a single magnetic sensor5, or more than two magnetic sensors5(for example three magnetic sensors5).

During a preliminary step, the first, the second and the third detector10,20,30are paired to associate them and configured so as to assign to each a function in the detection method S. For example, for the first gate, the first detector10can be configured as the master detector whereas the second detector20is configured as the slave detector. For the second gate, the second detector20is configured as the master detector whereas the third detector30is configured as the slave detector. During the pairing, the means of identification of each detector of the system (typically, their address) are also entered and stored in the memory of each of the adjacent detectors. Thus, the means of identification of the first detector10are entered into the second detector20whereas the means of identifying the second detector20are entered into the first detector10so as to permit their pairing. In the same way, the means of identifying the second detector20are entered into the third detector30, whereas the means of identifying the third detector30are entered into the second detector20.

During a first step, one at least from among the first, second and third magnetic sensors5detects a magnetic field and generates a signal representative of an intensity of the magnetic field thus detected.

In practice, all the magnetic sensors5of one same gate generate, continuously or periodically, a signal representative of an intensity of a magnetic field, only the power of the signal generated by each sensor5being different.

In the remainder of the text, an example wherein a signal is generated by the two second magnetic sensors5and the two third magnetic sensors5is described to illustrate the steps of the method S.

The signal generated by the magnetic sensors5is then transmitted to the processing unit6of the master detector of the gate in question, where applicable by way of communication interfaces7. In the example described, the signal generated by the three magnetic sensors5is transmitted by the communication interface7of the third detector30to the processing unit6of the second detector20. The signal generated by the second magnetic sensors5is itself transmitted directly to the processing unit6of the second detector20(bearing in mind that it would be transmitted via its communication interface7should the processing unit6be external).

During a second step, the processing unit6of the master detector of the concerned gate, here the second detector20, computes a corrected value (step S3) of the signals generated by each of the magnetic sensors5by applying an attenuation coefficient to said signals. Here, the processing unit6therefore computes a first corrected value corresponding to a first of the pairs of second and third magnetic sensors5and a second corrected value corresponding to the second of the pairs.

Then, the processing unit6computes a value corresponding to the sum of the values of the signals thus corrected (or in a variant determines the maximum value of the corrected signals, for each pair of sensors5). This correction step having already been described above in relation to the sub-steps S31 to S35, it will not be further detailed here.

Alternatively, instead of computing a corrected value of the signals of each pair of magnetic sensors5, the processing unit6can compute an average value PGS[2, 3] of the signals generated for each pair of magnetic sensors5. Here, the processing unit6therefore computes a first average value corresponding to a first of the pairs of second and third magnetic sensors5and a second average value corresponding to the second of the pairs.

Of course, when the detectors each comprise only a single sensor5, the processing unit6computes only a single average value corresponding to the average value of the signals of these two magnetic sensors5.

As indicated above, the processing unit6can compute an arithmetic mean value of the signals or, in a variant, a geometric mean value.

In another variant, the processing unit6can at once compute an average value of the signals for each pair of magnetic sensors5and implement a step of correcting said signals, as described above so as to obtain a corrected average value.

In a similar way to that already described, the correction step S2 can be applied either to the signals generated by the sensors5, or to the sum of the signals (or to their maximum value), or to the average value of the signals.

During a third step, when one of the values PGS[2, 3] computed in the second step is greater than the predetermined threshold value, the processing unit6of the second detector20transmits to the processing unit6of the first detector10on the one hand said computed value PGS[2, 3] and on the other hand the signals generated by its second magnetic sensors5.

During a fourth step, simultaneous with the third step, the processing unit6of the first detector10computes a value PGS[1, 2] on the basis of the signals generated for each pair of magnetic sensors5of the first gate. The computation of the value carried out by the processing unit6of the first detector10is the same as that carried out by the processing unit6of the second detector20. In other words, when one of the master detectors computes a corrected value (corresponding to the sum of the corrected values, to a maximum corrected value or else to a corrected and averaged value respectively), the other master detectors carry out the same computation (sum of the corrected values, a maximum corrected value or else a corrected and averaged value, respectively).

Here, the processing unit6of the first detector10computes, for example, a first corrected average value corresponding to a first of the pairs of first and second magnetic sensors5, and a second corrected average value corresponding to the second pair so as to obtain corrected average values of the signals.

When the value PGS[1, 2] computed by the first detector10is less than the predetermined threshold value, the processing unit6of the first detector10does not send any instructions to generate an alarm to the emitters8of the first detector10or of the second detector20.

On the other hand, when the value PGS[1, 2] computed by the first detector10is greater than the predetermined threshold value, during a fifth step, the processing unit6of the first detector10, as master detector of the first gate, determines if the target object has been detected by the first gate (formed by the first and the second detector10,20) or by the second gate (formed by the second and the third detector20,30).

To do this, the processing unit6of the first detector10compares the computed values PGS[2, 3] (sum of the corrected values, corrected maximum values or else a corrected and averaged value) by the second detector20and the values PGS[1, 2] computed by the first detector10.

For this purpose, during a first sub-step, the processing unit6of the first detector10multiplies the value PGS[2, 3] computed on the basis of the signals generated by the second and third sensors5by a predefined safety coefficient Ks:Ks*PGS[2, 3]. The safety coefficient Ks is greater than or equal to 1, for example equal to 1.5 or 2.

In parallel, during a second sub-step, the processing unit6of the second detector10multiplies the value PGS[1, 2] computed on the basis of the signals generated by the first and second sensors5by the predefined safety coefficient Ks:Ks*PGS[1, 2].

During a third sub-step, the first detector10compares the value PGS[1, 2] with the value Ks*PGS[2, 3] which it has computed on the basis of the signals generated by the first and second sensors5. If the value PGS[1, 2] computed on the basis of the signals generated by the first and second sensors5is less than the value Ks*PGS[2, 3] obtained by multiplying the safety coefficient Ks by the value computed on the basis of the signals generated by the second and third sensors5(i.e. if PGS[1, 2]<Ks*PGS[2, 3]), the processing unit6of the first detector10deletes or does not send any instructions to generate an alarm to the emitters8of the first and the second detector10,20.

In parallel, during a fourth sub-step, the second detector20compares the value PGS[2, 3] with the value Ks*PGS[1, 2] obtained by multiplying Ks by the value of the signals generated by the first and second sensors5. If the value PGS[2, 3] computed on the basis of the signals generated by the second and third sensors5is less than the value Ks*PGS[1, 2] obtained by multiplying the safety coefficient Ks by the value computed on the basis of the signals generated by the first and second sensors5(i.e. if PGS[2, 3]<Ks*PGS[1, 2]), the processing unit6of the second detector20deletes or does not send any instructions to generate an alarm to the emitters8of the second and the third detector20,30. In the contrary case, if PGS[2, 3]>Ks*PGS[1, 2], the second detector2sends instructions to transmit an alarm to the emitters8of the second detector20and the third detector30.

An operator can then easily identify which gate (here, the second) has detected a target object.

It should be noted that the application of a safety coefficient Ks during the comparison of the values computed by the detectors on either side of a given gate confers a margin in the detection of the target objects and reduces the risks of false alarms.

Thus, the sending to the master detector of a gate, by the slave detector of this gate, of the computed value (sum of the corrected values, corrected maximum values or else a corrected and averaged value) for the adjacent gate, for which this same detector is master, makes it possible to determine the location of the target object which has been detected. It will specifically be recalled that the detection by the magnetic sensors5is scalar and that a detector sharing two adjacent gates (here the second detector20) is not capable of determining on what side the target object that it has detected is located.

The detection method S of the invention can be generalized to cover any detection system1comprising m detectors, where m is greater than or equal to 4 in such a way as to form m−1 gates and where two adjacent gates have one and the same detector in common.

The detection method S then comprises the same steps as those described previously concerning a detection system1with three detectors. However, in this case, when a detector n−1 has computed a value PGS[n−1; n] greater than the predetermined threshold value AT, the detection method S comprises, in addition to the steps of comparing this value PGS[n−1; n] and that computed by the detector n−2 (PGS[n−2; n−1]), a step of comparing this value PGS[n−1; n] with that computed by the detector n (PGS[n; n+1]) in order to determine the gate within which a target object has been detected (seeFIG.7). Where applicable, the safety coefficient Ks (Ks≥1) is applied to the value PGS[n; n+1] during the comparison step.

For example, the detector n−1 computes a given value PGS[n−1; n], typically a corrected average value, on the basis of the signals generated by the magnetic sensors5of the detectors n and n−1. The detector n−1 (as the slave detector) then sends this computed value PGS[n−1; n] to the detector n−2 (as the master detector) as well as the values of the signals generated by its magnetic sensors5. The detector n−2 then computes a value PGS[n−2; n−1], here a corrected average value, on the basis of the values of the signals generated by the magnetic sensors5of the detectors n−2 and n−1. In the same way, the detector n (as the slave detector of the detector n−1) computes and sends the computed value PGS[n; n+1] to the detector n−1 as well as the values of the signals generated by its magnetic sensors5. If the value computed by the detector n−2 (as the master detector) is greater than the predetermined threshold value:the detector n−2:multiplies the value PGS[n−1; n] computed and transmitted by the detector n−1 by the safety coefficient Ks andcompares the value that it has computed PGS[n−2; n−1] with the value that it has multiplied Ks*PGS[n−1; n]. If the value PGS[n−2; n−1] that it has computed is less than the value computed by the detector n−1 and multiplied by the coefficient Ks (i.e. if PGS[n−2; n−1]<Ks*PGS[n−1; n]), the detector n−2 deduces therefrom that no alarm must be generated by the gate formed by the detectors n−2 and n−1. The detector n−2 therefore does not send any instructions to generate an alarm to the emitters8of the detectors n−2 and n−1 (or, where applicable, cancels the instructions to emit an alarm).the detector n−1, in parallel:multiplies the value PGS[n−2; n−1] computed and transmitted by the detector n−2 by the safety coefficient Ks andcompares the value that it has computed PGS[n−1; n] with the value that it has multiplied Ks*PGS[n−2; n−1].If the value PGS[n−1; n] that it has computed is less than the value computed by the detector n−2 and multiplied by the coefficient Ks (i.e. if PGS[n−1; n]<Ks*PGS[n−2; n−1]), the detector n−1 deduces therefrom that no alarm must be generated by the gate formed by the detectors n−1 and n. The detector n−1 therefore does not send any instructions to generate an alarm to the emitters8of the detectors n−1 and n (or, where applicable, cancels the instructions to emit an alarm).multiplies the value PGS[n; n+1] computed and transmitted by the detector n by the safety coefficient Ks andcompares the value it has computed PGS[n−1; n] with the value that it has multiplied Ks*PGS[n; n+1].If the value PGS[n−1; n] that it has computed is less than the value computed by the detector n and multiplied by the coefficient Ks (i.e. if PGS[n−1; n]<Ks*PGS[n; n+1]), the detector n−1 deduces therefrom that no alarm must be generated by the gate formed by the detectors n−1 and n. The detector n−1 therefore does not send any instructions to generate an alarm to the emitters8of the detectors n−1 and n (or, where applicable, cancels the instructions to emit an alarm).the detector n, in parallel:multiplies the value PGS[n−1; n] computed and transmitted by the detector n−1 by the safety coefficient Ks andcompares the value that it has computed PGS[n; n+1] with the value that it has multiplied Ks*PGS[n−1; n].If the value PGS[n; n+1] that it has computed is less than the value computed by the detector n−1 and multiplied by the coefficient Ks (i.e. if PGS[n; n+1]<Ks*PGS[n−1; n]), the detector n deduces therefrom that no alarm must be generated by the gate formed by the detectors n and n+1. The detector n therefore does not send any instructions to generate an alarm to the emitters8of the detectors n and n+1 (or, where applicable, cancels the instructions to emit an alarm).

It should be noted that, when the adjacent gates do not share one and the same detector and are each formed by two separate detectors, the detection is done within each gate by the pairs of detectors. Thus the detectors of a given gate do not necessarily communicate with the detectors of an adjacent gate. This is because each gate can operate independently, since it is not necessary to determine the gate through which the target object has passed.