Acoustic Roughness Measurement of Railway Tracks: Laboratory Investigation of External Disturbances on the Chord-Method with an Optical Measurement Approach

Abstract

For acoustic roughness monitoring of the railway network at train travelling speed, new direct measurement methods are required. Common direct measurement methods need the blocking of track sections, as they are based on manually operated devices. Indirect measurement methods such as accelerometer or microphone measurements can be installed on the train, but require a conversion of the obtained measurement data to rail roughness. Optical measurement methods allow a direct measurement from the moving train, even at higher speeds, due to the contact-free nature of the measurement. This paper investigates the influence of various disturbances on the measurement result, which are expected on the train. The frequently used chord method deploying laser triangulation sensors is used. Four sensors are integrated into the setup, thus providing the possibility to combine the results from four chord methods. The measurements of the optical system are compared with a tactile measurement of METAS (Swiss Federal Institute of Metrology) on a test bench equipped with a reference rail segment. It is shown that dust and water on the rail have a significant influence in the range of small wavelengths. Displacements and tilting of the sensor array, as well as vibrations, can be compensated to a certain level by the chord method, while a single sensor is significantly disturbed. The combination of four different chord lengths and selection of the theoretically optimal method for each one-third octave band shows an improvement of the measurement result. Based on the observations made, recommendations for practical tests on the train are concluded.

Acoustic Roughness Measurement of Railway Tracks: Implementation of a Chord-Based Optical Measurement System on a Train

“…For the optimized method, the mean deviation was 3.74 dB. A comparable situation was obtained for test stand measurements with a wet rail, as experimentally illustrated by Mauz et al [18]. The spectrum of acoustic roughness for a measured section compared with the reference section B is shown in Figure 8.…”

“…The distances between the sensors were the following: 168 mm (sensor 1 to 2), 113 mm (sensor 2 to 3) and 105 mm (sensor 3 to 4). The identical longitudinal distances between the sensors on the sensor plate were used in the laboratory experiments as described by Mauz et al [18]. Four chord methods were evaluated, including their combination hereafter referenced as the optimized method.…”

“…The single-chord method, the 3AP1 (Three-Point Asymmetrical 1) method, as described by Mauz et al [18], was compared with the optimized method. The reference section was traversed with the calculated velocity of 79.6 km h −1 .…”

“…Measurement can be carried out without calibration measurements and at the line speed of a measuring vehicle. The functionality of the approach was demonstrated by Mauz et al [18] in laboratory tests on a test bench based on the chord method described by Grassie [19]. In laboratory tests, only low train speeds and artificial external disturbances of the train were tested.…”

Dynamic calibration method for track geometry measurement system-a case study in China

“…This method is commonly used in countries such as Germany and Japan. The chord measurement method is often used in countries such as Switzerland and Austria, which measures the deviation from the ideal chord [7]. Another common method is the laser detection system, which uses high-precision lasers and optical instruments to detect track defects and misalignments [8].…”