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Development of a new wheel independent speed sensor for trains
Umeå University, Faculty of Science and Technology, Department of Physics.
2017 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

A ballasted railway track consists primarily of two rails discretely supported by sleepers. When a train passes over a sleeper a small vertical force arises due to the dynamic stiffness of the track. This force can be detected by an accelerometer mounted on the train. By analyzing the frequency content of the accelerometer data, it is possible to determine at what frequency the train is passing the sleepers. The train speed is obtained by multiplying this frequency with the distance between the sleepers. This work focuses on the development of an algorithm which identifies and tracks the measured vertical accelerations corresponding to the sleeper crossings, to produce an estimate of the train speed.

The frequency content of the measured vertical accelerations are analyzed by performing a Fourier transform. A Blackman-Harris window is used to ensure periodicity of the signal and the signal is zero-padded to increase frequency resolution. The search for the sleeper crossing frequency is constrained using knowledge of the previous speed estimate when available and the maximum vehicle acceleration. The peak in the frequency spectrum which corresponds to the sleeper crossings has been observed to be the largest peak within the region of interest, especially at higher speeds. The root mean square value of the vertical accelerations were used as a criterion for standstill as this was observed to be a good indicator of movement.

Two mounting locations for the accelerometer have been investigated; the axle-box and the car-body. The axle-box is the preferred mounting location due to the higher amplitude of the vertical accelerations which makes it possible identify sleeper crossings at lower speeds. It has also been found that the usage of combing two accelerometers improved the overall result.

Measurements have been received from the tracks at Stockholm metro and the high-speed train Zefiro on the Velim test track, Czech Republic. Using the Zefiro measurements, the algorithm shows very promising results and can continuously track the sleeper passing peak with an error estimate of ±  m/s. The Stockholm metro measurements posed a more difficult case since there were many start and stops at low speeds, but the algorithm follows the sleeper passing peak except for a few cases where the estimate becomes temporarily erroneous.

Place, publisher, year, edition, pages
2017.
National Category
Signal Processing
Identifiers
URN: urn:nbn:se:umu:diva-138809OAI: oai:DiVA.org:umu-138809DiVA: diva2:1137518
External cooperation
Bombardier Transportation
Subject / course
Examensarbete i teknisk fysik
Educational program
Master of Science Programme in Engineering Physics
Presentation
2017-08-25, Universitetsklubben, Umeå University, Umeå, 11:00 (Swedish)
Supervisors
Examiners
Available from: 2017-08-31 Created: 2017-08-31 Last updated: 2017-08-31Bibliographically approved

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