Fabry–Pérot Interferometer Monitoring System for Counting Train Axle

A measurement component based on fiber Fabry–Pérot (FP) interferometer integrated into a monitoring system for train axle counting is demonstrated. To better understand the characteristics of the sensors and their suitability for rail transport, two sensors with slightly different sensitivities were placed on the foot of the rail in the middle of the sleepers. During the measurement campaign that was carried out on Slovakia regional railway line, the sensors registered passage of the trainset more than 70 times, and their speeds were in the range of approximately from 15 to 65 km/h. The trainset consists of a diesel locomotive and four wagons with different weights and different wears. The traces were divided into five groups according to speeds, while the actual speed differs from the average one by ±1 km/h. Traces obtained by the sensors were filtered. Subsequently, the phase of the signal was obtained and interpolated, and the derivation of the function was performed. If the maximal value of the first derivation of the function is observed, then the axle (wheel) is identified. In case of good technical condition of the vehicle, it is possible to determine the number of axles regardless of the vehicle speed (in our measurement campaign up to 65 km/h and real operation up to 98 km/h) and sensitivity of the sensor. In addition, the noise level in the trace can tell us something about the vehicle’s technical condition.