Train Wheel Detection Systems: Present Technologies and Future Trends

PATRICIO G. DONATO; JESÚS UREÑA

Railway Transportation: Policies, Technology and Perspectives

Novascience

Lugar: Nueva York (EEUU); Año: 2009; p. 279 - 302

Safe automation and traffic control are two of  the main R&D lines in the railways scope. New technologies in infrastructure and vehicles require more sophisticated railway signalling systems. Train wheel detectors or axle counters perform an essential safety function in the railway signalling system. These modules can detect the  passing of a train over critical points, also known as detection points, along the railway network without using any vehicle-mounted device. The train wheel detectors are used to determine  the train position and direction, to measure its speed, to confirm track circuits and treadles,  among others. Almost all commercial electronic train wheel detectors use magnetic or inductive devices as physical sensors. Most of them are based on RLC circuits located next to the rail at the detection points, where the impedance of the sensor is directly related to the magnetic permeability of the physical medium. Other train wheel detectors use a pair of coils (located on either side of the rail) at each detection point, which work as emitter and receiver. The interruptions in the magnetic flux between the coils are used as a detection signal in these cases. Over the past few years, new solutions based on the use of coded signals and new sensor array implementations for magnetic or inductive train wheel detectors have been proposed. These novel detection systems allow to work with low signal-to-noise ratios (SNR) without the presence of signal processing electronic equipment near the track. Train wheel detectors based on non-magnetic principles, such as fiber optic or infrared (IR) sensors, have also been proposed and developed. These new technologies are aimed at ensuring reliability levels similar to those of magnetic or inductive detectors, while reducing maintenance tasks and costs. Future developments in the field should encourage new or improved solutions for critical aspects regarding railway safety applications, such as: multiple detection points, fault tolerance, robustness regarding external noise, interferences from other sources and attenuation of wires, and easy installation and maintenance tasks.