Exploration Of Using FBG Sensor For Axle Counter In...

Exploration of Using FBG Sensor for Axle Counter in
Railway Engineering
K.Y. LEE, K.K. LEE, S.L. HO
Department of Electrical Engineering, The Hong Kong Polytechnic University
Hung Hom, Hong Kong SAR, CHINA

Abstract: - Fibre Bragg Grating (FBG) sensors are finding increasing applications in smart structures.

They can be embedded in civil structures such as bridges, buildings etc for the detection and monitoring of parameters such as strain, pressure and temperature. It allows assessments on the integrity of structures at various manufacturing and construction stages, and facilitates health management of many important structures in their subsequent operations. However, their application in railway engineering is rare. This paper explores the technical feasibility and potential usage of FBG sensor for axle counter application in railway engineering. In essence, an axle counter system is used for counting the number of train axles coming in and out of a section of rail track. Field tests have been carried out and concluded that FBG is having great potential for replacing conventional railway axle counter system, which is based on the principles of magnetic field disturbance technology as the wheels are passing by.
FBG axle counter have lots of advantages over their conventional counterparts due to its electrical immunity to noise, multiplexing capability, compactness and more importantly, its relatively low cost of construction. Provided there is a weather proof and robust mounting methodology in the next phase, the FBG axle counter will become a strong competitor to conventional systems. Once the physical integrity of FBG systems is proven to be satisfactorily, one can extend its application to build a smart railway, particularly as part of a new generation of signaling systems.
Key-Words : - Fibre Bragg Grating, Axle Counter, Train Detection & Identification

1 Introduction
Railway engineers are understandably very conservative in the use of any new technology for train operations. Only proven technology with good track record will be used. Any change to the conventional equipment and methodology must be brought-in under a technically and commercially prudent manner.
Fibre Bragg Grating (FBG) technology has been widely adopted in smart structure engineering with good records. Its application on railway engineering is limited at this stage, although there are applications in, for example, the monitoring of the strain/stress on the train bogie frame composite structure [1]. An in-depth review on the FBG characteristic revealed that it can bring massive benefits to railway operation by giving additional train operational information to rolling stock engineers and signaling engineers in the monitoring and planning of the train traffic. One of its possible

applications is on the railway axle counter in tracks. Due to its unique construction nature, the cost of FBG axle counter is relatively low when compared with those of conventional technologies that are used to provide the same technical and operational information. There is a good future in using FBG axle counter to operate a smart railway service.

2 Fibre Bragg Grating Technology
The fabrication of refractive index grating is reported by Hill et al. in 1978 [2]. Subsequently,
Meltz et al. devise a method to controll the fabrication of grating using UV laser [3].
Basically, when a germanium-doped silica core fibre is exposed to ultraviolet (UV) radiation
(with wavelength around 240 nm), it produces a permanent change in the refractive index of the germanium-doped region, due to the photosensitivity nature of the fibre and, using such an exposure, it is possible to obtain realize

changes in the refractive index by factors as large as 10-3 in germanium-doped silica fibre. If the fibre is exposed to a pair of interfering UV beams as shown below, then in regions of constructive interference which

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Exploration Of Using FBG Sensor For Axle Counter In Railway Engineering

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Exploration Of Using FBG Sensor For Axle Counter In Railway Engineering

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