EP0024978B1 - Method and system for detecting landslip(s) on railways - Google Patents

Abstract

1. Method for detecting landslip(s) on railway tracks, characterized in that the vibrations induced by the landlip(s) in at least one rail of the track are detected, the rail being used as the mechanical transducer and transmitter letting through preferentially at least one band of rail natural frequencies detected to set off an alarm signal system, and in that the detection system is neutralized each time a train passes.

Description

The invention relates to safety on railway tracks and in particular to the detection of landslides likely to occur in tunnels and tracks in trenches or open to such a threat by the environment, with a view to signaling them. The invention also relates to the detection of approaching trains.

The use of seismographic type safety devices has the disadvantage that the transmission of tremors due to a landslide is very quickly absorbed by the ground, which implies a prohibitive multiplication of equipment and possible causes of failure.

The detection device according to FR-A-2 206 224 uses a vibration sensor cooperating with a rail and associated with a low-pass filter detection circuit to eliminate the signals appearing at the natural frequency of the rail, which limits its use to the detection of the passage of a train and excludes any detection of landslides on the railway track and any detection of approaching trains.

The landslide detection device according to US-A-2187518 comprises a barrier to be installed next to the railway track and provided with an electrical contact reacting to the mechanical deformation of the barrier in the event of a landslide. The installation of such a barrier is bulky and expensive and the barrier is not reliable. Train approach detection is not possible.

The subject of the present invention is a method for detecting landslides on a railway track, the implementation of which requires only relatively small apparatus for good detection quality.

The detection method according to the invention of landslide (s) on a railway track, is characterized in that the vibrations induced by the landslide or landslides are detected in at least one rail of the track, used as a mechanical transducer and preferred transmitter at least one specific frequency band of the rail detected to trigger an alarm signaling, and that the detection is neutralized each time the train passes.

The detection device based on such a method is characterized in that it comprises a vibration sensor intended to be fixed on the side of a rail and producing electrical output signals as a function of the detected vibrations, means for amplifying the signals produced by the sensor, at least one bandpass filter adjusted to a frequency band having a privileged propagation in the rails of the track and connected to the output of said amplification means, a device for switching a signaling of alarm responding to a certain level of signal at the output of the bandpass filter, and means for neutralizing the operation of the device that can be actuated at each passage of the train.

Preferably, the detection device according to the invention comprises two bandpass filters in parallel, these two filters being adjusted to the frequency bands which have been found to encompass the main frequency domains generated in the rails by the phenomena to be detected , or on the one hand, 1100 to 1500 Hz and, on the other hand, 6400 to 9600 Hz for the rails normally used in France.

In the absence of said means for neutralizing its operation, the device is applicable to the detection of approaching trains, which can in particular be useful for the protection of yards on track.

• la figure 1 est une vue schématique illustrative de la fixation prévue du capteur de vibrations sur un rail ;
• la figure 2 est un schéma de principe d'un dispositif de détection selon l'invention ;
• la figure 3 est un schéma électrique de détail d'un ensemble de circuits associés au capteur de vibrations et faisant suite à un amplificateur de charge de ce dernier.

The invention is moreover hereinafter more fully described in an embodiment of a detection device which is given thereof, by way of example only, with reference to the attached drawings, in which:

• Figure 1 is a schematic illustrative view of the intended attachment of the vibration sensor on a rail;
• Figure 2 is a block diagram of a detection device according to the invention;
• Figure 3 is a detailed electrical diagram of a set of circuits associated with the vibration sensor and following a charge amplifier of the latter.

The detection device according to the invention uses a vibration sensor, preferably constituted by a piezoelectric accelerometer of known type, covering a range of frequencies from 0 to 9,700 Hz, and having a sensitivity of 20 mV / g.

This accelerometer, designated by 1 as a whole and provided with an output connector 1a, is intended to be fixed, as illustrated in FIG. 1, on the external flank of the head 2 of a rail 3 of the track, which has proven to be the best vibration detection area on the rail.

This fixing is carried out here by means of a mount adapting to the shoe 4 of the rail and now the base of the accelerometer resting elastically on the side of the mushroom 2 by means of a spring 5. The frame forms a sort of support bracket, one branch of which constitutes a sole plate 6 which can be engaged under the pad 4 between two track crosspieces and having one end 7 which forms a hook for gripping an edge of the pad, while a clamping toad 8 is provided on the other edge of the shoe, mounted on a stud 9 which the sole carries and lockable with a nut 10 and lock nut 11. The toad 8 has an oblong slot 12 d 'engagement on the stud 9, allowing the possible adaptation of the frame to any form of pad that may be encountered. The other branch 13 of the support bracket has an oblong slot 14 at its upper part which is traversed by the threaded tail 15 of a guide piece 16 of the spring 5 for holding the accelerometer 1. The positioning of the latter can thus be carried out by adjusting the threaded shank 15 in the slot 14, before it is blocked by a nut 17 and lock nut 18.

With this accelerometer is associated a charge amplifier, designated by 19 in FIG. 2 and which can be of any known type, making it possible in particular to obtain a voltage gain of 1000. Thus, a vibration resulting in an acceleration of 0.1 - 10- ³ g can lead in this example to a peak voltage of 2 mV at the output of said charge amplifier.

The output of the charge amplifier 19, which provides a signal on low impedance, is connected to a vibration analysis circuit which will be seen later, via an input amplifier designated by 20 as a whole and which is here constituted, as illustrated in FIG. 3, using a differential amplifier 21 whose inverting input is connected to the output of the amplifier 19 by a resistor 22 and the input non-inverting to ground by a resistor 23, while a feedback loop provided between non-inverting output and input comprises, in parallel, a resistor 24 of impedance here a hundred times higher than that of resistor 22 and two limitation diodes 25, 26 arranged head to tail. Such an amplifier 20 has a high gain for weak signals (40 dB without saturation). At strong signals, its response becomes logarithmic and the signal is written by diodes 25-26 in order to avoid a risk of saturation of the stages of the vibration analysis circuit.

The latter here comprises two bandpass filters designated by 27 and 28 as a whole, arranged in parallel and to the inputs of which the output of the differential amplifier 21 is connected, the bandpass 27 being adjusted to the frequencies from 1100 to 1,500 Hz and bandpass 28 on frequencies from 6,400 to 9,600 Hz.

Each band pass filter is here composed (see fig. 3) of a high pass filter 27a or 28a followed by a low pass filter 27b or 28b, each of these high pass or low pass filters being here constituted by a filter of well-known type, the diagram of which will not be described further on and of which it will be sufficient to recall that the resistances connectable at the choice of these filters, respectively designated by 29 for the filter 27a, 30 for the filter 27b, 31 for the filter 28a and 32 for the filter 28b, determine with the associated capacitors 33 the cut-off frequency of these filters, while the high-pass output is taken from the output of the first differential amplifier constituting each filter while the output passes -bas is taken from the output of the last differential amplifier of each filter.

Thus, the filters are adjusted so that the high-pass filter 27a transmits to the low-pass filter 27b only the frequencies above 1100 Hz, the latter blocking the frequencies above 1500 Hz, so that its pass-through output low 34 transmits only frequencies between 1100 and 1500 Hz.

Similarly, the high-pass filter 28a transmits to the low-pass filter 28b only frequencies above about 6,400 Hz, the latter blocking frequencies above 9,600 Hz, so that its low-pass output 35 only transmits than frequencies between 6400 and 9600 Hz.

As shown in FIG. 2, the outputs of the bandpass filters 27, 28 can then be simply connected by an adaptation amplifier 36 to a switching device 37 for alarm signaling, which can take various forms.

In particular, this switching device 37 will be provided with memory or self-maintenance in response to any detection of landslides where the phenomenon is of a temporary nature but where the signaling must remain until security check and remedy brought to the incident.

Alarm signaling can also take various forms.

It may be a luminous visual signaling 38 provided on the track at an appropriate distance from the detector, or a signaling calling on the well-known track safety circuit known as an “luminous automatic block”, with track sections which can be short-circuited by the passage of trains, the signaling of landslides then resulting from the maintained closure of a circuit for short-circuiting the track section or sections adjacent to the area protected by the detector or more of them.

As memory switching device 37 actuated by the output of amplifier 36, it is thus possible in particular to use a trigger thyristor controlled by said output, a bistable flip-flop with control input linked to said output and with initialization or return input. at rest with manual control, or a self-sustaining relay with manual de-excitation control.

An example of a relay switching device is given in FIG. 3, in which an amplifier assembly also serving as a rectifier is provided for supplying a relay 39 with direct current, the closing contact 40 of which is placed on the supply circuit of the light signaling 38 and of which the reopening contact 41 with manual control is placed on its self-maintenance circuit.

This amplifier-rectifier assembly comprises at the output 34, 35 of each bandpass filter 27, 28 a separator amplifier 42 followed by a peak detector amplifier 43, the outputs of the latter being both connected to the input terminal of relay 39 solenoid.

Each separating amplifier 42 is formed using a differential amplifier 42a driven at its non-inverting input and arranged to have a gain of approximately 10dB.

Each peak detector amplifier 43 is constituted by means of a differential amplifier 43a driven on its non-inverting input by means of a writing diode 44 in derivation with respect to which a resistance circuit 45 is arranged. and capacitor 46 having a time constant RC of the order of 0.1 S, so that the capacitor 46 forms a capacitor continuous supply tank of the non-inverting input of the differential amplifier 43a when it is loaded by the half-waves passing through the clipping diode. This amplifier 43a also has a resistance feedback loop 47 between output and inverting input, which here gives it a gain of about 27 dB.

Thus, in response to the vibratory excitation of the accelerometer 1 and to a certain level of signal at the output of the bandpass filters 27 and / or 28, the solenoid of the relay 39 is notably supplied with inrush direct current. and maintaining its closing contact activating the light signaling 38.

As an indication, with an overall gain of the circuit of Figure 3 corresponding to 70 dB and for an output level of 5 V necessary to actuate the relay 39, a voltage of 2 mV is sufficient at the input of this circuit, which, taking into account the aforementioned characteristics of the accelerometer and its charge amplifier, corresponds to an acceleration threshold in transverse bending of the rail head of 0.1 mg.

Detection distances ranging from 200 to 300 and even 500 meters have thus been obtained experimentally, by simulating landslides by falling material of a nature and minimum quantity capable of causing an obstruction in a tunnel, depending on whether the fall affects the ballast alone, the ballast and at least one cross member, or the detection rail.

Of course, such a landslide detection device (s) must be neutralized in good time for the passage of the trains, and this can simply be done by track equipment with conventional pedal contacts actuated by the trains as they pass, in order to cut the electrical supply of the detection or signaling on a sufficient distance to avoid any untimely actuation coming from the vibrations induced in the rail by the rolling of the train (a margin of one kilometer compared to the protected zone seems to be largely sufficient in any case).

Finally, such a detection device is also applicable, as already mentioned, to the detection of approaching trains, for which a detection signaled at an average distance of 500 meters has been obtained experimentally, the alarm signaling then being sound in the case of sites under way.

It will be noted that with the circuit described in FIG. 3, it is then possible to use only a simple relay for switching the audible alarm, that is to say without self-maintenance, so that this emergency signaling will operate automatically before and until after a certain time in relation to the passage of the train in front of the detection device in question, without human intervention on it.

Of course, various alternative embodiments of such a detection device or its operating mode can be imagined without departing from the scope of the invention.

Claims (7)

1. Method for detecting landslip(s) on railway tracks, characterized in that the vibrations induced by the landlip(s) in at least one rail of the track are detected, the rail being used as the mechanical transducer and transmitter letting through preferentially at least one band of rail natural frequencies detected to set off an alarm signal system, and in that the detection system is neutralized each time a train passes.

2. System for detecting landslip(s) on railways, characterized in that it comprises a vibration sensor designed to be fixed on the side of a rail and producing electrical output signals which depend on the vibrations detected, means of amplifying the signals produced by the sensor, at least one band-pass filter set to a band of frequencies preferentially propagated through the track rails and connected to the output of the said amplification means, an alarm signal switching system responding to a certain signal level on the band-pass filter output and means of neutralizing operation of the system which can be operated each time a train passes.

3. The detection system according to claim 2, characterized in that the vibration sensor is a piezoelectric accelerometer designed to be fixed to the outer side of the rail head.

4. The detection system according to either of claims 2 or 3, characterized in that the band-pass filter is set to the 1 100 to 1 500 Hz frequency band.

5. The detection device according to either of claims 2 or 3, characterized in that it comprises two parallel band-pass filters, one of the filters being set to the 1 100 to 1 500 Hz frequency band and the other to the 6 400 to 9 600 Hz frequency band.

6. The detection device according to any of claims 2 to 5, characterized in that a matching or adaptation amplifier which may also rectify, is inserted between the band-pass filter(s) and the switching system.

7. The application of the detection system according to any of claims 2, 3, 4, 5 or 6 to the detection of approaching trains in the absence of the said means of neutralizing its operation.

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