EP0391775A1 - Device for the detection of the passage of at least one moving body at at least one determinate point of its displacement - Google Patents

Abstract

The invention relates to a device for detecting the passage of at least one moving body at at least one determinate point of its displacement along a trajectory inside a space through reference to which the said displacements of the moving body are evaluated. <??>It is characterised in that: - on the one hand, the dual reception circuit (29) included in the responder, includes two members (20, 21) generating, on the passage of the moving body at the monitored point, two signals (31, 32) of substantially equivalent kind and, - on the other hand, these members (20, 21) are designed and interconnected in such a way as to confer opposite values upon at least one of the characteristics of these signals (31, 32), which on being combined, form at least one resultant signal (R), at least one characteristic of which, at at least one predetermined point of the passage of the transmitter in line with the responder, varies in an abrupt manner in accordance with an amplitude of variation which is discernible from the possible other variations in the relevant characteristic of the said resultant signal (R) so as to thus constitute an, in particular, electrical phenomenon, termed the synchronising pulse, which demarcates two distinct portions within the resultant signal (R), each of a certain duration. <IMAGE>

Description

The invention relates to a device for detecting the passage of at least one mobile at at least one determined point of its movement along a trajectory inside a space by reference to which the said movements of the mobile.

It applies in particular to the detection of the passage of guided means of transport at determined points on their route with a view, for example:
- to readjust the positioning and / or speed calculation devices operating using conventional means, subject to error, for example by sliding,
- identify at least one mobile and / or at least one point on the route.

Numerous devices are already known for the purpose of detecting the passage of at least one mobile in at least one determined area of a space in which said mobile operates (FR-A-2,195,812 and 2,593,761).

These devices each include two separate parts, namely an interrogation unit and an answering machine, these two separate parts being one associated with the mobile, the other considered fixed in the space with respect to which the mobile is moving.

The interrogation assembly itself comprises a transmission assembly and a reception assembly.

It is obviously connected to circuits for processing the information received as a function of the applications targeted and to perform these functions, this interrogation assembly and the processing circuits are connected to a supply of electrical energy.

One of the problems long posed but resolved to date is notably that of arriving at an answering machine which is said to be passive because it feeds on the signal received from the interrogation assembly and that consequently, it is without its own electric power supply, either by batteries or by connection to a distribution network.
In one of these known devices (FR-A-2.195.812):
- the interrogation unit comprises, on the one hand, turned towards the zone where the passage of the transponder is monitored by two transmitters, one of a high frequency signal in the form of an electromagnetic wave, the another of a signal of lower frequency which, in this example, creates an electrostatic field and, on the other hand, a receiver of the signal worked out by the responder from the signals received from the transmitters during its passage in the aforementioned zone then immediately reissued by said responder,
- The transponder mainly comprises antenna elements to which a non-linear component such as a diode known for its ability to modify and in particular to mix the signals received before their retransmission to the receiver in the form of a modulated carrier is connected.

The receiver then demodulates this signal and processes its lower frequency component.

Designed for application to surveillance at the exit of a store from the passage of articles carrying a sensitive label making the answering machine, this device uses a set of interrogation whose dimensions are incompatible with the limits in particular of template imposed in applications to means of transport and above all are sensitive to the presence of the answering machine in a very large space and therefore lack the precision necessary to, for example, reset positioning indicators but again and above all can be disturbed by the means of monitoring a parallel channel, all the more since it gives no information on the direction of movement.

In another device known to date (FR-A-2,593,761), the interrogation assembly comprises:
a means of amplitude modulation of a high frequency signal and of fairly high power (approximately 10 GHz and 200 mW) using a medium frequency signal (approximately 200 KHz) chopping the carrier all or nothing at rhythm of the frequency of the wave produced by an oscillator and
- Means for transmitting this high frequency carrier thus pre-modulated in amplitude towards the point where the passage of the answering machine in its movement relative to the interrogation assembly is monitored.

This interrogation assembly also comprises means for receiving at least one high frequency carrier overmodulated in amplitude by the answering machine which, when it passes to the point monitored by the interrogation assembly receives the signal transmitted and, at the using a circulator, distribute:
- a fraction in a channel where a circuit restores the clock signals and applies them to a delay line which will therefore phase them by a certain value, less than the width of the pulses, and
- another fraction in a channel where the already modulated carrier will again be cut by the pulses of the delay line.

It is the carrier thus doubly cut out which is immediately retransmitted by the responder to the receiver which demodulates and processes the signal by phase comparison.

With such devices, it is known to personalize the answering machines in order to identify at least one mobile or at least one point of its movement.

For this, the delay line of the various responders has its time constant which is adapted and the phase comparator of the interrogation assembly receives references specific to each possible phase shift.

To be able to determine the direction of movement of the mobile, it is also known to use an answering machine comprising two signal reception circuits and which are spaced from one another in a direction parallel to the trajectory of the mobile.

An advantageous arrangement known to the receiving circuits of the answering machine is a so-called symmetrical arrangement, that is to say at the same distance on either side of the re-transmitting antenna of the answering machine.

Given the small footprint that the circuits must have, these are produced in the form of a printed circuit.

The drawbacks of this known device are the disturbances by signals from channels parallel to that being monitored and above all a precision in determining the passage of the mobile at the right of the determined point of its trajectory which is still insufficient taking into account the requirements of the means, in particular IT loaded. to process the information received for example to determine the speed and ensure the registration of the cinemometric sensors.

One of the results that the invention aims to obtain is a device of the type mentioned above which is very precise without calling on more expensive or fragile components than the devices known to date.

To this end, it relates to such a device notably characterized in that:
on the one hand, the double reception circuit which the answering machine comprises, comprises two members generating, when the mobile passes through the monitored point, two signals of substantially equivalent nature and,
- on the other hand, these members are designed and interconnected so as to give at least one of the characteristics of these signals opposite values which, by combining, form at least one resulting signal including at least one characteristic, at at least one predetermined point in the passage from the transmitter to the right of the responder, varies abruptly according to an amplitude of variation discernible from any other variations of the characteristic considered of said resulting signal for thus constituting a particularly electrical phenomenon hereinafter called top which delimits in the resulting signal two separate parts each of a certain duration.

• - figure 1 : le principe général du dispositif de l'invention,
• - figure 2 : une variante préférée de réalisation de ce dispositif,
• - figure 3 : le détail des composants de l'ensemble d'interrogation,
• - figure 4 : le schéma synoptique de l'antenne du répondeur,
• - figure 5 : le schéma synoptique de réalisation de l'antenne du répondeur dans une variante de réalisation.
• - figures 6 à 9 : différents graphes de variation en fonction du temps de l'enveloppe de signaux exploités dans le dispositif de l'invention.

The invention will be better understood with the aid of the description below given by way of nonlimiting example with regard to the attached drawing which represents:

• - Figure 1: the general principle of the device of the invention,
• FIG. 2: a preferred variant embodiment of this device,
• - Figure 3: details of the components of the interrogation assembly,
• - Figure 4: the block diagram of the answering machine antenna,
• - Figure 5: the block diagram of the answering machine antenna in an alternative embodiment.
• - Figures 6 to 9: different graphs of variation as a function of time of the envelope of signals used in the device of the invention.

Referring to the drawing, it can be seen that the device 1 for detecting the passage of at least one mobile 2 at at least one determined point 3 of its movement, along a trajectory 4 inside a space by report to which we appreciate the said movements of the mobile, conventionally comprises two separate sets 5, 6 namely an interrogation set 5 and an answering machine 6, these two separate sets being one associated with the mobile, the other considered fixed in particular on a support 6 _has substantially continuous located along the path along which the mobile moves.

In the example shown, it is the interrogation unit 5 which is associated with the mobile 2 and the answering machine 6 which is fixed but, without departing from the scope of the invention, the interrogation unit can be fixed and the mobile answering machine.

The interrogation assembly 5 which itself comprises a transmission assembly 7 and a reception assembly 8 is connected to a means 9 for processing the information received and, to perform these functions, this assembly is connected to a source (not shown) of electrical energy supply.

The responder 6, on the other hand, is of the so-called passive type because it does not have a supply of clean electrical energy, whether by battery or by connection to a distribution network.

It therefore feeds on the signal received from the interrogation unit.

The transmission assembly 7 comprises two transmitters 10, 11 the emissions of which are directed substantially towards a point 12 fixed relative to the interrogation assembly where the passage of a point 13 is monitored as for it fixed with respect to the answering machine.

One of these points 12, 13 can constantly be substantially confused with point 3 of the trajectory where the passage of the mobile 2 is monitored.

On the other hand, the points 12, 13 are not confused until the mobile moves to the determined point 3 of the trajectory 4.

One (10) of the transmitters 10, 11 transmits a high frequency signal 14 in the form of an electromagnetic wave, the other 11 transmits a lower frequency signal 15.

They each include a source 16, 17 and an antenna 18, 19 adapted and tuned to the transmitted frequency.

The responder 6 mainly comprises elements 20, 21, 22 of antennas adapted and tuned to the reception of the aforementioned signals 14, 15 to which elements is connected a non-linear component 23 such as a diode which, as soon as the responder receives the two aforementioned signals , in a known manner, mixes them and immediately retransmits this mixture, in the form of a modulated carrier 24, to at least one antenna 25 which obviously includes the receiver 8.

In the example shown, in the interrogation assembly 5, the antenna 18 for transmitting a high frequency signal 14 and the antenna 25 for receiving the modulated carrier 24 are combined and, therefore, these antennas 18, 25 are connected to the high frequency source 16 and to the circuit 26 internal to the receiver 8 by a circulator 27.

In the case where several mobiles circulate on the trajectory 4, the device described above also comprises means 28 with a view to identifying at least one of these mobiles 2 and or at least one of the determined points 3 of the trajectory 4.

In order to be able to determine the direction of movement of the mobile, the responder 6 comprises a double circuit 29 for receiving the same signal and the antennas 20, 21 of this double circuit are spaced from one another in at least one direction substantially parallel to the path of the mobile.

Preferably, the two antennas 20, 21 of this double circuit 29 of the answering machine are arranged substantially symmetrically, that is to say at the same distance on either side of its retransmission antenna 22.

They are produced in the form of printed circuits.

According to an essential characteristic of the invention:
on the one hand, the dual reception circuit 29 which the answering machine comprises comprises two members 20, 21 generating, when the mobile passes through the monitored point, two signals 31, 32 of substantially equivalent nature and,
- on the other hand, these members 20, 21 are designed and interconnected so as to give at least one of the characteristics of these signals 31, 32 opposite values which, when combined, form at least one resulting signal R of which at least one characteristic, at at least one predetermined point 3, 13 of the passage from the transmitter 5 to the right of the responder 6, varies abruptly according to an amplitude of variation discernible from any other variations of the characteristic considered of said signal resulting R to thus constitute a phenomenon in particular electrical hereafter called top 30 which delimits in the resulting signal R two distinct parts R _a , R _b each of a certain duration T₁ and T₂.

According to a characteristic of the invention:
the lower frequency signal 15 is transmitted by the corresponding transmission assembly 7 in the form of a magnetic field using an antenna 19 carrying out a primary winding 19 and,
- the two antennas 20, 21 of the dual circuit 29 for receiving the answering machine, adapted and tuned for this frequency:
. on the one hand, constitute two secondary windings 20, 21 which are arranged so, during the passage of the primary winding 19, not only to be each subjected to the field magnetic emitted by said primary winding but still so, in an intermediate stage, to be both simultaneously subjected to it and,
. on the other hand, are associated in opposition so as, in the intermediate stage of the passage of the primary winding 19, to create in these secondary windings 20, 21, simultaneously subjected to the magnetic field, induced currents 31, 32 of substantially equal absolute values but opposite signs.

The resulting signal R which, in this case, is an induced electric current, is thus obtained according to the principle of the differential transformer according to which a primary winding 19 sends energy to two secondary windings 20, 21.

In fact, these secondary windings being associated in opposition and arranged one next to the other along the path of the mobile which carries the primary winding 19, when said primary winding 19 is above one of the secondary windings 20, 21, it makes it possible to obtain in this secondary winding a current 31, 32 of a certain absolute value but always of opposite phase to that which will be created in the other secondary winding in a symmetrical situation of the primary winding.

When the primary winding 19 passes between the two secondary windings 20, 21, as a function of the displacement of the primary winding 19 on the axis of the trajectory, one of the secondary currents undergoes a decrease while the other undergoes a growth.

As in the case of the invention, the extent of the primary winding 19 and / or the distance which separates the two secondary windings 20, 21 is, along the path 4, such that, at least in an intermediate position of the primary winding 19 with respect to the secondary windings 20, 21, the said primary winding 19 induces in the two secondary windings currents which, once combined to produce the resulting signal R, cancel each other out in particular due to their opposite phases and this during a duration T₀ depending in particular on the speed of the relative movement of the transmitter 5 and the responder 6 along the trajectory 4.

It is this design of the double circuit 29 which makes it possible to generate at least one top 30 of duration T₀ easily recognizable and guaranteeing by the brutality of its occurrence the precision of the detection.

To facilitate understanding of this phenomenon, a certain number of graphs (FIGS. 6 to 9) have been plotted as a function of time of the envelope of signals used in the device of the invention, which graphs are calibrated on a same origin of time.

In particular in FIGS. 6 and 7, the graphs showing the evolution of a characteristic of each of the currents 31, 32 induced in the two secondary windings 20, 21 are considered in absolute value.

In FIG. 8, the graph of the evolution of the resulting signal R is represented, that is to say the current composed with the two currents 31, 32 induced in the secondary windings 20, 21 also taken in absolute value.

In Figure 9, there is shown one of the graphs of the signal retransmitted by the responder when it is activated by the interrogation unit.

As it appears, the top 30 which is discussed further is framed by two parts of the resulting signal which extend over respective durations T₁ and T₂.

Although this is not shown, it is understood that the durations T₁ and T₂ of the parts framing the top 30 are equal when the windings are identical.

In a preferred embodiment, the two windings 20, 21 are asymmetrical so as to generate, whatever the speed of movement of the mobile, signals 31, 32 of different durations between them in order to give the parts R _a , R _b of the resulting signal R which surround the top 30 of the durations T₁ and T₂ themselves different and therefore discernible, and,
- On the one hand, the windings 20, 21 of each responder located on the trajectory are oriented in a predetermined manner and known to the interrogation assembly in such a way that during the processing by the responder of the parts R _a , R _b of the resulting signal R characterizes the direction of movement of the interrogation assembly with respect to said responder and,
- on the other hand, the processing means 9 of the interrogation assembly comprises:
. at least one means 33, 34 generating pulses according to a predetermined frequency,
. at least one means 35, 36 for counting the numbers N₁, N₂ of pulses delivered by the generator means during the duration of at least one of the components of the resulting signal that are the parts R _a , R _b and the top 30 which are transcribed in the signal 24 sent by the answering machine,
. at least one means 37 for comparing between them the numbers N₁, N₂ of counted pulses and for producing at least one signal 39 reflecting the state of the comparison and therefore characterizing the direction of passage of the mobile.

Preferably:
on the one hand, the interrogation assembly comprises at least one means 40 for measuring the speed of movement of the mobile which is independent of its processing means 9 and generates at least one signal 41 proportional to the speed and,
- on the other hand, the processing means comprises several means 33, 34 pulse generators of which at least one 33 uses the signal 41 of the means 40 for measuring the speed and generates pulses at a frequency proportional to the said speed so that the means 35 for counting the pulses during the duration of at least one of the components of the resulting signal which are the parts R _a , R _b and the top 30 transcribed in the signal 24 transmitted by the responder, take into account the numbers N₁, N₂ of pulses whose orders of magnitude are independent of the speed of the mobile.

By this, the direction of movement can finally be determined without error.

The means for measuring the speed of the mobile which influences the pulse generator means is for example of the type based on Doppler kinemometry.

Preferably, to determine the instantaneous speed V of the vehicle during its passage to the right of the answering machine, the means for processing the interrogation assembly comprises on the one hand at least one means 34 generating pulses according to a predetermined frequency and , on the other hand, at least one means 36 for counting the pulses at least during the duration of at least one of the components of the resulting signal that are the parts R _a , R _b and the top 30, which are transcribed in the signal 24 emitted by the responder.

The frequency of the pulses generated by the above-mentioned means 34 is preferably fixed.

This redundancy of counts thus makes it possible to secure the information collected and to increase its accuracy.

Advantageously, the high frequency signal is located among the lowest frequencies in the hyper-frequency band.

Preferably, the high frequency signal is of the order of 1 GHz and its power is very low and, for example, of only 40 mW which limits the risk of creating radio interference and allows the emissions to be located at within the most stringent radio standards in this area.

As for the so-called lower frequency signal, it is chosen from the range of medium frequencies of the order of 1 to 10 MHz and, for example, around 4 MHz.

Optimization of the functioning of the answering system is achieved by the following elements:
- a flat double differential winding 20, 21, tuned to a medium frequency, favoring the magnetic field,
- a plated microwave antenna 22, favoring the electromagnetic wave,
- a component 23 (diode) characterized by its non-linearity properties,
- Elements 42 of impedance adaptation (auto transformer plug) allowing the maximum energy to be transmitted to the diode and elements 43, 44 of insulation (line section in constant distributed).

The assembly is carried out on a standard printed circuit in epoxy glass.

For the retransmission by means of a hertzian link, towards the interrogator, of the signal characteristic of the presence of an answering machine at the right of this one, at the passage of the vehicle in a predetermined place of the course, the answering machine ensures the transposition of its differential characteristic into very high frequency in order to benefit from the electromagnetic radiation properties and the low powers required.

For this very high frequency, the responder is equipped with a single broadband antenna making it possible to receive a carrier frequency and retransmit to the interrogator the first harmonics created by the responder.

This plated type antenna is placed between the two aforementioned secondary windings in order to make the best use of the large radiation diagram that it provides and to generate it in place of the magnetic field linked to the windings.

In addition, the dimensions of the assembly are reduced accordingly.

Advantageously, the responders can by construction be tuned to different medium frequencies so as to create digital words.

The medium frequency transmitter will then supply the different frequencies required by means of printed coils.

In the center of these is the plated microwave antenna, of the dipole type for example.

The "antenna" transmission subsystem thus consists of transmission frames excited by one or more medium frequency sources and a single high frequency antenna excited by a suitable source.

Preferably, the coupling of the mid-frequency transmitter and the responder is carried out with critical coupling in order to allow the assembly to work on a wider frequency band.

According to the invention, each responder comprises:
at least one means 28 for storing at least one message, in particular a digital message,
at least one means 45 for modulating the signal 24 sent by said responder to the interrogation unit as a function of the message contained in the storage means.

For example, according to the invention, on the one hand, the means 45 for modulating the signal 24 consists of an oscillator 46 and the message storage means consists of at least one register shift memory and on the other hand, these modulation 45 and storage means 28 draw their operating energy from the lower frequency signal received by the responder.

Advantageously and in order to overcome problems with the height of the vehicle body with respect to the track, the receiving means of the interrogator comprise:
at least one means 47 such as a power divider which separates the signal received from the answering machine by the interrogation assembly into two channels,
at least one means 48, 49 which, in particular synchronized with the high frequency signal produced in the corresponding source 16, induces a phase shift of pi / 2 between the signals which circulate on each of the aforementioned channels,
- at least one means 50, 51 raising at least one of the characteristics of each signal squared,
at least one means 52 summing the characteristics of the signals squared and producing a compound signal addressed to the means 9 for processing the interrogation assembly.

The microwave antenna 22 has a large radiation diagram which makes it possible to cover the medium frequency and bandwidth fields sufficiently wide to allow the spectral lines of the first harmonics to pass.

In the drawing, we also notice the impedance adaptation and line isolation elements in the environment of the mixing diode.

The answering machine circuit is mounted in a plastic case, transparent to microwave waves and the magnetic field and robust enough to withstand the more or less severe vibrations occurring during the passage of vehicles at high speed as well as projections of all kinds. : water, grease, oil. . .

Claims (10)

1. Device (1) for detecting the passage of at least one mobile (2) at at least one determined point (3) of its movement, along a trajectory (4) inside a space by report to which we appreciate the said movements of the mobile conventionally comprising two separate sets (5, 6), namely an interrogation set (5) and an answering machine (6), these two separate sets being one associated with the mobile, the another considered fixed in particular on a support (6 _a) located substantially continuous along the path (4) in which the mobile moves,
in which device:
- the interrogation assembly (5) which itself comprises a transmission assembly (7) and a reception assembly (8) is connected to a means (9) for processing the information received and, to ensure these functions, this assembly is connected to a source of electrical energy supply,
on the other hand, the responder (6) is of the so-called passive type due to the fact that it lacks a supply of clean electrical energy, whether by battery or by connection to a distribution network,
- the transmission assembly (7) comprises two transmitters (10, 11) whose emissions are directed substantially towards the point (12) fixed relative to the interrogation assembly where the passage of a point is monitored ( 13) meanwhile fixed with respect to the answering machine, one (10) of the transmitters (10, 11) emitting a high frequency signal (14) in the form of an electromagnetic wave, the other (11) emitting a signal of lower frequency (15), these transmitters each comprising a source (16, 17) and an antenna (18, 19) adapted and tuned to the above frequency,
- the answering machine (6) includes:
. a double circuit (29) for receiving the same signal and the antennas (20, 21) of this double circuit are spaced from one another in a direction at least substantially parallel to the path of the mobile,
. mainly elements (20, 21, 22) of antennas adapted and tuned to the reception of the aforementioned signals (14, 15) to which elements is connected a non-linear component (23) such as a diode which, as soon as the answering machine receives the two aforementioned signals, in a known manner, mixes them up and immediately retransmits this mixture, in the form of a modulated carrier (24), to at least one antenna (25) which the receiver (8),
in which device possibly:
the interrogation assembly comprises means (28) for identifying at least one of the mobiles (2) and or at least one of the determined points (3) of its trajectory (4),
the antennas of the dual circuit of the answering machine are arranged substantially symmetrically, that is to say at the same distance on either side of its retransmission antenna (22),
this device being CHARACTERIZED in that:
on the one hand, the double reception circuit (29) which the answering machine comprises, comprises two members (20, 21) generating, when the mobile passes by at the monitored point, two signals (31, 32) of substantially equivalent nature and,
- on the other hand, these members (20, 21) are designed and interconnected so as to give at least one of the characteristics of these signals (31, 32) opposite values which, when combined, form at at least one resulting signal (R) of which at least one characteristic, at at least one predetermined point (3, 13) of the passage from the transmitter (5) to the right of the responder (6), varies abruptly according to an amplitude of variation discernible from any other variations of the characteristic considered of said resulting signal (R) to thus constitute a phenomenon in particular electrical hereinafter called top (30) which delimits in the resulting signal (R) two parts (R _a , R _b ) each of a certain duration (T₁ and T₂). 2. Device according to claim 1 characterized in that:
the lower frequency signal (15) is transmitted by the transmission assembly (7) in the form of a magnetic field using an antenna (19) carrying out a primary winding (19) and ,
- the two antennas (20, 21) of the dual circuit (29) for receiving the answering machine, adapted and tuned for this frequency:
. on the one hand, constitute two secondary windings (20, 21) which are arranged so, during the passage of the primary winding (19), not only to be each subjected to the magnetic field emitted by said primary winding but also so, in an intermediate stage, to be both simultaneously submitted to it and,
. on the other hand, are associated in opposition so as, in the intermediate stage of the passage of the primary winding (19), to create, in these secondary windings (20, 21), subjected simultaneously to the magnetic field, induced currents (31, 32) of substantially equal absolute values but of opposite signs. 3. Device according to claim 2 characterized in that the two windings (20, 21) are asymmetrical so as to generate, whatever the speed of movement of the mobile, signals (31, 32) of different durations between them in view to give to the parts (R _a , R _b ) of the resulting signal (R) which frame the top (30) of the durations (T₁ and T₂) which are themselves different and therefore discernible and,
- on the one hand, the windings (20, 21) of each responder located on the trajectory are oriented in a predetermined manner and known to the interrogation assembly so that during the processing by the responder of the parts (R _a , R _b ) of the resulting signal (R) characterizes the direction of movement of the interrogation assembly with respect to said responder and,
- on the other hand, the processing means (9) of the interrogation assembly comprises:
. at least one means (33, 34) generating pulses according to a predetermined frequency,
. at least one means (35, 36) for counting the numbers (N₁, N₂) of pulses delivered by the generator means during the duration of at least one of the components of the resulting signal which are the parts (R _a , R _b ) and the top (30) which are transcribed in the signal (24) emitted by the answering machine,
. at least one means (37) for comparing between them the numbers (N₁, N₂) of counted pulses and for producing at least one signal (39) reflecting the state of the comparison and therefore characterizing the direction of passage of the mobile. 4. Device according to claim 3 characterized in that to determine the instantaneous speed (V) of the vehicle during its passage to the right of the answering machine, the means for processing the interrogation assembly comprises on the one hand at least one means (34) pulse generator at a predetermined frequency and, on the other hand, at least one means (36) for counting the pulses at least during the duration of at least one of the components of the resulting signal which are the parts (R _a , R _b ) and the top (30) which are transcribed in the signal (24) sent by the answering machine. 5. Device according to any one of claims 1 to 4 characterized in that the high frequency signal is located among the lowest frequencies of the hyper-frequency band. 6. Device according to claim 5 characterized in that the high frequency signal is of the order of 1 GHz and its power is very low and, for example, only 40 mW which limits the risk of creating radio interference. 7. Device according to any one of claims 1 to 6 characterized in that the so-called lower frequency signal is chosen from the range of medium frequencies of the order of 1 to 10 MHz and, for example, around 4 MHz. 8. Device according to any one of claims 1 to 7 characterized in that the high-frequency antenna of the answering machine:
- is placed between the two aforementioned secondary windings (20, 21) in order to make the best use of the large radiation diagram that it provides and to generate it in place of the magnetic field linked to the windings,
- is of a broadband type enabling a carrier frequency to be received and the first harmonics created by the responder to be transmitted back to the interrogator. 9. Device according to any one of claims 1 to 8 characterized in that the receiving means of the interrogator comprise:
- at least one means (47) such as a power divider which separates the signal received from the answering machine by the interrogation unit into two channels,
- at least one means (48, 49) which, in particular synchronized with the high frequency signal produced by the corresponding source (16), induces a phase shift of pi / 2 between the signals which circulate on each of the aforementioned channels,
- at least one means (50, 51) squaring at least one of the characteristics of each signal,
- At least one means (52) summing the characteristics of the signals squared and producing a compound signal addressed to the means (9) for processing the interrogation assembly. 10. Device according to any one of claims 1 to 9 characterized in that each answering machine comprises: - at least one means (28) for storing at least one message, in particular a digital message,
- At least one means (45) for modulating the signal (24) transmitted by said responder to the interrogation unit as a function of the message contained in the storage means.

Images