Edge-filter technique and dominant frequency analysis for high-speed railway monitoring with fiber Bragg gratings

Abstract

Structural health and operation monitoring are of growing interest in the development of railway networks. Conventional systems of infrastructure monitoring already exist (e.g. axle counters, track circuits) but present some drawbacks. Alternative solutions are therefore studied and developed. In this field, optical fiber sensors, and more particularly fiber Bragg grating (FBG) sensors, are particularly relevant due to their immunity to electromagnetic fields and simple wavelength-division-multiplexing capability. Field trials conducted up to now have demonstrated that FBG sensors provide useful information about train composition, positioning, speed, acceleration and weigh-in-motion estimations. Nevertheless, for practical deployment, cost-effectiveness should be ensured, specifically at the interrogator side that has also to be fast (>1 kHz repetition rate), accurate (∼1 pm wavelength shift) and reliable. To reach this objective, we propose in this paper to associate a low cost and high-speed interrogator coupled with an adequate signal-processing algorithm to dynamically monitor cascaded wavelength-multiplexed FBGs and to accurately capture the parameters of interest for railway traffic monitoring. This method has been field-tested with a Redondo Optics Inc. interrogator based on the well-known edge-filter demodulation technique. To determine the train speed from the raw data, a dominant frequency analysis has been implemented. Using this original method, we show that we can retrieve the speed of the trains, even when the time history strain signature is strongly affected by the measurement noise. The results are assessed by complimentary data obtained from a spectrometer-based FBG interrogator.

Railway monitoring system using optical fiber grating accelerometers

“…The relationship between the main geometry of the train (i.e. wheel set spacing, bogie spacing and carriage length) and the spectral content of rail vibration has already been demonstrated and successfully validated in a previous work [5]. The periodicity of the axle (L a ), the bogie (L b ), and the cars (L c ) lead to three different amplitude modulations of the spectrum having corresponding frequency components, f a , f b , and f c .…”

“…In these systems, as a train passes, the number of axles is counted. Two of such subsequent counting units determine whether the train is on a particular section or not [4][5][6]. The conventional technology to realize axle counting is based on magnetic sensors.…”

“…Through real time field trials, usage of FBG sensors has already been demonstrated as a feasible solution in train identification, axle counting, defect determination, flat wheel detection, measurement of lateral displacement, speed and acceleration estimation [5][6][7][8][9][10][11][12]. In almost all of these demonstrations, the FBG sensors were manually placed on particular locations (or orientations) and bonded to the foot of the rail (ideally between a sleeper bay [13]).…”

Coupled-core fiber Bragg gratings for low-cost sensing

“…To reduce the cost of the interrogation of FBG sensors, changes in the position of λ B can be converted to intensity changes by means of edge filters 7 , 13 – 15 , interferometers 16 , 17 , or similar wavelength-selective devices 18 in combination with inexpensive photodetectors. The so-called π-phase-shifted FBGs interrogated with narrow linewidth lasers have been proposed to develop intensity-modulated sensors 19 – 24 .…”

Low-Cost Interrogation Technique for Dynamic Measurements with FBG-Based Devices

“…Commercial OFS interrogators (designed based on a scanning laser or scanning filters) are able to probe the FBG spectrum with higher resolution and scanning frequency. However, they become extremely expensive whenever hundreds of scans per second are required [ 16 ]. Several solutions for dynamic monitoring have been proposed.…”