Detection of anomalies in rail wheelsets
This application relates to methods and apparatus for the detection of anomalies in the wheelsets of rail vehicles, for instance for detection of defects such as wheel flats ( 303 ) of a wheel ( 301 ). The method using a distributed acoustic sensor ( 106 ) having a sensing optical fiber ( 104 ) deployed along at least part of a rail track ( 201 ) as a train ( 202 ) moves along that part of the track. The distributed acoustic sensor detects acoustic signals from a plurality of longitudinal sensing portions of the sensing optical fiber. A processor 108 analyzes the acoustic signals to determine the train speed v. Having determined the train speed the processor also analyzes the acoustic signals for a characteristic acoustic signal so as to detect an anomaly in a wheelset where the characteristic acoustic signal is based on the determined train speed. In particular the method may involve at least a first section of track where the train travels with a first speed v 1 and a second section of track where the train travels with a second different speed v 2 the characteristic acoustic signal may be a repetitive signal at a frequency that varies proportional to the train speed.
1. A method of detecting an anomaly in a wheelset of a train comprising:
taking data acquired by a distributed acoustic sensor having a sensing optical fibre deployed along at least part of a rail track as the train moves along that part of the track, wherein the data corresponds to acoustic signals detected by a plurality of longitudinal sensing portions of said sensing optical fibre;
analysing the acoustic signals to determine the train speed comprising identifying at least a first section of track where the train travels with a first speed and a second section of track where the train travels with a second different speed; and
analysing the acoustic signals from the longitudinal sensing portions for a characteristic acoustic signal so as to detect an anomaly in a wheelset comprising analysing the acoustic signals from the longitudinal sensing portions from the first section of track based on the first speed and analysing the acoustic signals from the longitudinal sensing portions from the second section of track based on the second speed to detect a repetitive signal at a frequency that varies proportional to the train speed;
wherein said characteristic acoustic signal is based on the determined train.
2. A method as claimed in claim 1 wherein said characteristic acoustic signal comprises a repetitive signal having a characteristic frequency proportional to the determined train speed and a characteristic value.
3. A method as claimed in claim 1 wherein said characteristic acoustic signal comprises a first repetitive signal in the acoustic signals from the longitudinal sensing portions from the first section of track having a characteristic frequency proportional to the first train speed and a characteristic value and a second repetitive signal in the acoustic signals from the longitudinal sensing portions from the second section of track having a characteristic frequency proportional to the second train speed and the same characteristic value.
4. A method as claimed in claim 2 wherein the characteristic value corresponds to a rotational parameter for a rotating component of the wheelset, the rotational parameter is related to the extent of rotation of that rotating component as the train travels a given distance.
5. A method as claimed in claim 4 wherein analysing the acoustic signals for a characteristic acoustic signal comprises analysing the acoustic signals for a repetitive signal having a frequency that is within a range of characteristic frequencies, wherein said range of characteristic frequencies correspond to a range of values of said rotational parameter.
6. A method as claimed in claim 4 wherein analysing the acoustic signals for a characteristic acoustic signal comprises analysing the acoustic signals for a repetitive signal having a frequency that corresponds to one of a plurality of characteristic frequencies, wherein each characteristic frequency is based on a different values of the rotational parameter.
7. A method as claimed in claim 6 wherein at least some of said different values of rotational parameter correspond to different possible values for one component of the wheelset.
8. A method as claimed in claim 6 wherein at least some of said different values of rotational parameter correspond to values of rotational parameters for different components of the wheelset.
9. A method as claimed in claim 4 wherein the rotating component is a wheel and the rotational parameter is based on a known or estimated diameter of the wheel.
10. A method as claimed in claim 1 wherein analysing the acoustic signals from the longitudinal sensing portions for a characteristic acoustic signal comprises forming at least one measurement signal from the acoustic signals detected by different contributing sensing portions in a sequence, where the sensing portions are selected such that the position of the contributing sensing portion along the fibre moves with the train.
11. A method as claimed in claim 10 wherein the longitudinal sensing portions are selected in sequence based on the determined train speed.
12. A method as claimed in claim 1 comprising acquiring said data by using an interrogator unit to repeatedly interrogate the sensing optical fibre with one or more pulses of interrogating radiation, detect any interrogating radiation which is backscatter from within said fibre and processing said detected backscattered radiation to provide said data.
13. A method as claimed in claim 12 wherein said sensing optical fibre is deployed along a part of the rail track where changes in the speed of a train as it moves along the track are expected.
14. A computer program on a non-transitory storage medium comprising computer readable code for instructing a suitable computer to perform the method of claim 1 .
15. An apparatus for detecting an anomaly in a wheelset of a train comprising:
a distributed acoustic sensor interrogator unit for interrogating a sensing optical fibre deployed along at least part of a rail track as the train moves along that part of the track to provide data corresponding to acoustic signals detected by a plurality of longitudinal sensing portions of said sensing optical fibre; and
a processor configured to:
analyse the acoustic signals to determine the train speed comprising identifying at least a first section of track where the train travels with a first speed and a second section of track where the train travels with a second different speed; and
analyse the acoustic signals from the longitudinal sensing portions for a characteristic acoustic signal so as to detect an anomaly in a wheelset comprising analysing the acoustic signals from the longitudinal sensing portions from the first section of track based on the first speed and analysing the acoustic signals from the longitudinal sensing portions from the second section of track based on the second speed to detect a repetitive signal at a frequency that varies proportional to the train speed; wherein said characteristic acoustic signal is based on the determined train speed.
16. An apparatus as claimed in claim 15 wherein said characteristic acoustic signal comprises a first repetitive signal in the acoustic signals from the longitudinal sensing portions from the first section of track having a characteristic frequency proportional to the first train speed and a characteristic value and a second repetitive signal in the acoustic signals from the longitudinal sensing portions from the second section of track having a characteristic frequency proportional to the second train speed and the same characteristic value.
17. An apparatus as claimed in claim 16 wherein the characteristic value corresponds to a rotational parameter for a rotating component of the wheelset, the rotational parameter being related to the distance that the train must travel for one rotation of that rotating component.
18. An apparatus as claimed in claim 15 wherein said sensing optical fibre is deployed along a part of the rail track where changes in the speed of a train as it moves along the track are expected.