METHOD FOR MONITORING A RAILWAY TRACK AND MONITORING SYSTEM FOR MONITORING A RAILWAY TRACK

Abstract

A method for monitoring a railway track (11) is provided, the method comprising detecting monitoring signals (MS) by a distributed acoustic sensor (10) being arranged along the track (11), where each monitoring signal (MS) comprises a monitoring signal value (MSV) for a first measurement segment (12) of the distributed acoustic sensor (10) and a monitoring signal value (MSV) for a second measurement segment (22) of the distributed acoustic sensor (10), determining a first event monitoring signal value (EV1) for the first measurement segment (12) from the monitoring signal values (MSV) that are detected during the passage of a rail vehicle over the position of the first measurement segment (12), determining a second event monitoring signal value (EV2) for the second measurement segment (22) from the monitoring signal values (MSV) that are detected during the passage of a rail vehicle over the position of the second measurement segment (22), and determining a difference value (DV) where the difference value (DV) relates to the difference between an average relative value (ARV) and a relative value (RV), where the relative value (RV) is given by the relative difference between the first event monitoring signal value (EV1) and the second event monitoring signal value (EV2), wherein the average relative value (ARV) relates to an average value of relative values (RV) determined from previous passages of rail vehicles. Furthermore, a monitoring system (15) for monitoring a railway track (11) is provided.

Claims

1. A method for monitoring a railway track, the method comprising: detecting monitoring signals by a distributed acoustic sensor being arranged along the track, where each monitoring signal comprises a monitoring signal value for a first measurement segment of the distributed acoustic sensor and a monitoring signal value for a second measurement segment of the distributed acoustic sensor; determining a first event monitoring signal value for the first measurement segment from the monitoring signal values that are detected during the passage of a rail vehicle over the position of the first measurement segment; determining a second event monitoring signal value for the second measurement segment from the monitoring signal values that are detected during the passage of a rail vehicle over the position of the second measurement segment; and determining a difference value where the difference value relates to the difference between an average relative value and a relative value, where the relative value is given by the relative difference between the first event monitoring signal value and the second event monitoring signal value, wherein the average relative value relates to an average value of relative values determined from previous passages of rail vehicles.

2. The method for monitoring a railway track according to claim 1, wherein the distributed acoustic sensor comprises an optical fibre arranged along the track and the monitoring signals are backscattered signals of an input signal which is provided to the optical fibre.

3. The method for monitoring a railway track according to claim 1, wherein an upper threshold value is given by the product of the variance or standard deviation of the average relative value and a k-value, and it is determined if the difference value exceeds the upper threshold value.

4. The method for monitoring a railway track according to claim 1, wherein a lower threshold value is given by the product of the variance or standard deviation of the average relative value and an 1-value, and it is determined if the difference value is below the lower threshold value.

5. The method for monitoring a railway track according to claim 1, wherein the first measurement segment and the second measurement segment each relate to a predefined distance along the distributed acoustic sensor.

6. The method for monitoring a railway track according to claim 1, wherein the first event monitoring signal value is proportional to the sum of the energy emitted by the passing rail vehicle within the first measurement segment or the first event monitoring signal value is proportional to the average of the energy emitted by the passing rail vehicle within the first measurement segment .

7. The method for monitoring a railway track according to claim 1, wherein the relative difference relates to the respective ratio.

8. The method for monitoring a railway track according to claim 1, wherein each monitoring signal value is a signal-to-noise ratio.

9. The method for monitoring a railway track according to claim 1, wherein the method further comprises determining the velocity of a rail vehicle passing over the position of the first measurement segment and normalizing the first event monitoring signal value with respect to the velocity of the rail vehicle.

10. The method for monitoring a railway track according to claim 1, wherein for determining the relative values from previous passages of rail vehicles the position on the track of these rail vehicles is determined by employing further information about the movement of the rail vehicles.

11. The method for monitoring a railway track according to claim 1, wherein a correlation is determined between the average relative value and the relative value.

12. The method for monitoring a railway track according to claim 1, wherein a first correlation between the average relative value and the relative value is determined and wherein a second correlation between an average relative value of another track and the relative value is determined.

13. The method for monitoring a railway track according to claim 1, wherein the method is carried out for a plurality of first measurement segments and a plurality of second measurement segments.

14. The method for monitoring a railway track according to claim 1, wherein after determining a relative value, one of the relative values determined from previous passages of rail vehicles is replaced by said relative value.

15. A monitoring system for monitoring a railway track, the monitoring system comprising: an evaluation unit that is connected to a distributed acoustic sensor being arranged along the track, wherein the evaluation unit comprises a detection unit that is configured to receive monitoring signals that are detected by the distributed acoustic sensor, where each monitoring signal comprises a monitoring signal value for a first measurement segment of the distributed acoustic sensor and a monitoring signal value for a second measurement segment of the distributed acoustic sensor, the evaluation unit comprises an event unit that is configured to determine a first event monitoring signal value for the first measurement segment from the monitoring signal values that are detected during the passage of a rail vehicle over the position of the first measurement segment, and to determine a second event monitoring signal value for the second measurement segment from the monitoring signal values that are detected during the passage of a rail vehicle over the position of the second measurement segment, the evaluation unit comprises a comparator unit that is configured to determine a difference value where the difference value relates to the difference between an average relative value and a relative value, where the relative value is given by the relative difference between the first event monitoring signal value and the second event monitoring signal value, and the average relative value relates to an average value of relative values determined from previous passages of rail vehicles.

Description

[0050] The following description of figures may further illustrate and explain exemplary embodiments. Components that are functionally identical or have an identical effect are denoted by identical references. Identical or effectively identical components might be described only with respect to the figures where they occur first. Their description is not necessarily repeated in successive figures.

[0051] With FIG. 1 an exemplary embodiment of the method for monitoring a railway track is described.

[0052] FIGS. 2, 3 and 4 show exemplary embodiments of the monitoring system for monitoring a railway track.

[0053] FIGS. 5 and 6 show exemplary signals employed in the method for monitoring a railway track.

[0054] With FIG. 1 the steps of an exemplary embodiment of the method for monitoring a railway track 11 are described. The order of the steps can be different from the order provided here.

[0055] In a first step S1 initial monitoring signals are detected by a distributed acoustic sensor 10 that is arranged along the track 11. The initial monitoring signals are detected during the passage of rail vehicles on the track 11. The distributed acoustic sensor 10 is divided into a plurality of measurement segments 12, 22. Each measurement segment 12, 22 relates to a predefined distance along the distributed acoustic sensor 10. The initial monitoring signals are especially detected for a first measurement segment 12 and for a second measurement segment 22. Each initial monitoring signal comprises a plurality of initial monitoring signal values IV. Each initial monitoring signal comprises one initial monitoring signal value IV for each measurement segment 12, 22.

[0056] In a second step S2 first event monitoring signal values EV1 and second event monitoring signal values EV2 are determined. Each first event monitoring signal value EV1 is determined from the initial monitoring signal values IV that are detected during the passage of a rail vehicle over the position of the first measurement segment 12. For example, each first event monitoring signal value EV1 is proportional to the sum of the energy emitted by the passing rail vehicle within the first measurement segment 12 or the first event monitoring signal value EV1 is proportional to the average of the energy emitted by the passing rail vehicle within the first measurement segment 12. Each second event monitoring signal value EV2 is determined from the initial monitoring signal values IV that are detected during the passage of a rail vehicle over the position of the second measurement segment 22. For example, each second event monitoring signal value EV2 is proportional to the sum of the energy emitted by the passing rail vehicle within the second measurement segment 22 or the second event monitoring signal value EV2 is proportional to the average of the energy emitted by the passing rail vehicle within the second measurement segment 22.

[0057] For determining the initial monitoring signal values IV that are detected during the passage of one rail vehicle on the track 11 it is necessary to know where rail vehicles are moving on which track 11. The position along the track 11 of these rail vehicles can be determined by employing further information about the movement of the rail vehicles. These information are for example obtained by a further analysis of the monitoring signals MS. The step of detecting initial monitoring signal values IV and thus determining first and second event monitoring signal values EV1, Ev2 can be repeated several times. In this way, for each measurement segment 12, 22 a plurality of event monitoring signal values EV1, EV2 is obtained.

[0058] In a third step S3 relative values RV are determined. Each relative value RV relates to the relative difference between a first event monitoring signal value EV1 and a second event monitoring signal value EV2. The relative difference can be the respective ratio. From the relative values RV an average relative value ARV is determined. The average relative value ARV is an average value of the relative values RV. The average relative value ARV can be determined for each measurement segment 12, 22. The entirety of the average relative values ARV for one track 11 is referred to as the fingerprint of that track 11.

[0059] In a fourth step S4 monitoring signals MS are detected by the distributed acoustic sensor 10. Each monitoring signal MS comprises a monitoring signal value MSV for the first measurement segment 12 of the distributed acoustic sensor 10 and a monitoring signal value MSV for the second measurement segment 22 of the distributed acoustic sensor 10. Instead of the respective monitoring signal value MSV the signal-to-noise ratio of each monitoring signal value MSV can be employed in order to improve the accuracy of the method.

[0060] In a fifth step S5 a first event monitoring signal value EV1 for the first measurement segment 12 is determined from the monitoring signal values MSV that are detected during the passage of a rail vehicle over the position of the first measurement segment 12. Furthermore, a second event monitoring signal value EV2 for the second measurement segment 22 is determined from the monitoring signal values MSV that are detected during the passage of a rail vehicle over the position of the second measurement segment 22. For example, the first event monitoring signal value EV1 is proportional to the sum of the energy emitted by the passing rail vehicle within the first measurement segment 12 or the first event monitoring signal value EV1 is proportional to the average of the energy emitted by the passing rail vehicle within the first measurement segment 12. For example, each second event monitoring signal value EV2 is proportional to the sum of the energy emitted by the passing rail vehicle within the second measurement segment 22 or the second event monitoring signal value EV2 is proportional to the average of the energy emitted by the passing rail vehicle within the second measurement segment 22. This step can be repeated for a plurality of other measurement segments 12, 22. Each event monitoring signal value EV1, EV2 is proportional to the energy emitted by the respective passing rail vehicle within the respective measurement segment 12, 22.

[0061] In a sixth step S6 a relative value RV is determined. The relative value RV is given by the relative difference between the first event monitoring signal value EV1 and the second event monitoring signal value EV2 determined in the fifth step S5.

[0062] In a seventh step S7 a difference value DV is determined. The difference value DV relates to the difference between the average relative value ARV and the relative value RV. The average relative value ARV and the relative value RV are determined for the same two measurement segments 12, 22.

[0063] In an optional eighth step S8 the difference value DV is compared to an upper threshold value UT. The upper threshold value UT is given by the product of the variance of the average relative value ARV and a k-value, and it is determined if the difference value DV exceeds the upper threshold value UT. Furthermore, the difference value DV is compared to a lower threshold value LT. The lower threshold value LT is given by the product of the variance of the average relative value ARV and an l-value, and it is determined if the difference value DV is below the lower threshold value LT. In this way, deviations that are larger than typical deviations can be detected. If the difference value DV exceeds the upper threshold value UT or is below the lower threshold value LT a warning signal WS can be provided.

[0064] The accuracy of the method can further be improved by determining the velocity of a rail vehicle passing over the position of the first measurement segment 12 and normalizing the first event monitoring signal value EV1 with respect to the velocity of the rail vehicle. Moreover, the velocity of a rail vehicle passing over the position of the second measurement segment 22 can be determined and the second event monitoring signal value EV2 can be normalized with respect to the velocity of the rail vehicle.

[0065] In an optional further step of the method a correlation is determined between the average relative value ARV and the relative value RV. If several tracks 11 are arranged next to each other, for each track 11 a correlation between the average relative value ARV and the relative value RV is determined.

[0066] In order to further improve the accuracy of the method it is possible after determining a relative value RV to replace one of the relative values RV determined from previous passages of rail vehicles by said relative value RV. This update of the relative values RV can be done continuously. This means, for each measurement segment 12, 22 and for each determined relative value RV, the current relative value RV replaces one relative value RV for the respective measurement segment 12, 22. For example, in each case the oldest relative value RV is replaced. The total number of relative values RV can stay constant. It is further possible to replace relative values RV for selectable measurement segments 12, 22 by relative values RV that were determined after the relative values RV that are to be replaced. This manual replacement can be advantageous if a rail was repaired or a part of a rail was replaced. Therefore, the accuracy of the method is improved by replacing the relative values RV by relative values RV that were determined after the repair or replacement of the rail.

[0067] The method can be carried out for a plurality of first measurement segments 12 and a plurality of second measurement segments 22.

[0068] In FIG. 2 an exemplary embodiment of a monitoring system 15 for monitoring a railway track 11 is shown. The monitoring system 15 comprises an evaluation unit 16 that is connected to a distributed acoustic sensor 10 being arranged along the track 11. The evaluation unit 16 comprises an input 21 which is connected with an output 13 of the distributed acoustic sensor 10. The evaluation unit 16 comprises a detection unit 17 that is configured to receive monitoring signals MS that are detected by the distributed acoustic sensor 10, where each monitoring signal MS comprises a monitoring signal value MSV for a first measurement segment 12 of the distributed acoustic sensor 10 and a monitoring signal value MSV for a second measurement segment 22 of the distributed acoustic sensor 10. The evaluation unit 16 further comprises an event unit 18 that is configured to determine a first event monitoring signal value EV1 for the first measurement segment 12 from the monitoring signal values MSV that are detected during the passage of a rail vehicle over the position of the first measurement segment 12, and to determine a second event monitoring signal value EV2 for the second measurement segment 22 from the monitoring signal values MSV that are detected during the passage of a rail vehicle over the position of the second measurement segment 22. The detection unit 17 is connected with the event unit 18. The evaluation unit 16 further comprises a comparator unit 19 that is configured to determine a difference value DV where the difference value DV relates to the difference between an average relative value ARV and a relative value RV, where the relative value RV is given by the relative difference between the first event monitoring signal value EV1 and the second event monitoring signal value EV2. The comparator unit 19 is connected with the event unit 18. Furthermore, the comparator unit 19 is connected with a storage unit 20 where the average relative values ARV are stored. The comparator unit 19 is connected with an output 13 of the evaluation unit 16 where a warning signal WS can be provided. The monitoring system 15 can comprise the distributed acoustic sensor 10.

[0069] In FIG. 3 the embodiment of the monitoring system 15 is shown together with the distributed acoustic sensor 10 and a railway track 11. The evaluation unit 16 of the monitoring system 15 is connected with the distributed acoustic sensor 10. The distributed acoustic sensor 10 comprises an optical fibre 14 that is arranged along the track 11. Therefore, the monitoring signals MS are backscattered signals of an input signal IN which is provided to the optical fibre 14.

[0070] The distributed acoustic sensor 10 is divided into a plurality of measurement segments 12, 22. As an example four measurement segments 12, 22 are shown. Each measurement segment 12, 22 relates to a predefined length along the optical fibre 14 of the distributed acoustic sensor 10.

[0071] In FIG. 4 another exemplary embodiment of the monitoring system 15 is shown. The only difference to the embodiment shown in FIG. 3 is, that two tracks 11 are arranged next to each other. By employing the method described herein, it is possible to determine on which of the tracks 11 a rail vehicle is moving.

[0072] FIG. 5 shows average relative values ARV for one railway track 11. On the x-axis the distance along the track 11 is plotted in arbitrary units and on the y-axis the amplitude is plotted in arbitrary units. The solid line shows average relative values ARV plotted at their positions along the track 11. This means, this line is the fingerprint of the track 11. The dashed lines are relative values RV that are detected after the fingerprint was determined. For most of the measurement segments 12, 22 the relative values RV lie within the range of the average relative values ARV. However, for a few measurement segments 12, 22 the relative values RV are higher than the average relative values AV. A defect or a change of the rail at this position can be the reason for the increased relative values RV.

[0073] FIG. 6 shows average relative values ARV for two railway tracks 11. On the x-axis the distance along the tracks 11 is plotted in arbitrary units and on the y-axis the amplitude is plotted in arbitrary units. The solid line shows the average relative values ARV for a first track 11. The dashed line shows the average relative values ARV for a second track 11. It can be seen that the average relative values ARV significantly differ for the two tracks 11. Therefore, by employing the method described herein it is possible to distinguish on which of the tracks 11 a rail vehicle is moving.

REFERENCE NUMERALS

[0074] 10: distributed acoustic sensor [0075] 11: track [0076] 12: first measurement segment [0077] 13: output [0078] 14: optical fibre [0079] 15: monitoring system [0080] 16: evaluation unit [0081] 17: detection unit [0082] 18: event unit [0083] 19: comparator unit [0084] 20: storage unit [0085] 21: input [0086] 22: second measurement segment [0087] ARV: average relative value [0088] DV: difference value [0089] EV1: first event monitoring signal value [0090] EV2: second event monitoring signal value [0091] IN: input signal [0092] IV: initial monitoring signal value [0093] MS: monitoring signal [0094] MSV: monitoring signal value [0095] RV: relative value [0096] UT: upper threshold value [0097] LT: lower threshold value [0098] WS: warning signal [0099] S1-S8: steps