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How we created a solution to verify axle counters reliability in train detection systems

Home » Case studies » Axle counters verification
Client
Leading railway company
Completed
April 2021
Timeframe
6 months

Overview

Axle counters to be compliant with EN50617-2 standard

Axle counters are vital for safety of railway traffic. They inform about the position of trains and allow to correctly regulate access and crossings, avoiding any potential disruption or accident.

Tracks are divided on section blocks whose ends are delimited by sensors that detect when axles enter and exit these areas. These are magnetic field sensors detecting metallic wheels when passing by and must be compliant with EN 50617-2 standard about railway applications.

The coach includes equipment like condition air devices or power converters with very high currents that could generate magnetic fields. This can not interfere with functionalities and efficiency of axle counters, that shouldn’t be affected by external agents.

European official regulation states that essays must be conducted to simulate the situation of magnetic fields generated when the coach crosses axle counters, but it does not establish the ideal procedure to follow, it only suggests a possible working system.

However, the equipment and resources required for a lab to conduct these essays in that way is extremely high. It is difficult to be fully equipped for them, as most of centres do not invest in this because the volume of work in that area would not guarantee profitability of this high expense.

We realized that there was no lab in the country with a system able to perform this essay in full. We then decided to create our own by putting into practice some bright ideas, smart solutions to develop a complicated system out of few resources, but equally offering the levels required by the standard.

The challenge

Having our Lab to perform the essay making the most of the resources available

Solution

An alternative method:
Helmholtz coils

Implementation of this essay system is quite difficult due to the calibration needed on a first step. This process must be a vacuum calibration but that implies having the track itself, which is a ferromagnetic piece weighting around 54kg per meter and absorbing the magnetic field completely. To compensate this loss a very powerful system is needed.

Magnetic field is recreated with a coil, which allows the current to pass. This is the method suggested by the norm, but it requires a high power amplifier. But there is a technique consisting in making a coil out of turns: the Helmholtz coil. In this way a small amplifier is able to generate the field needed.

This system works fine with low frequencies, but for high frequences the power needed is increasingly higher. This essay starts on 10.000 Hz and ends on 1.300.000 Hz, with an increasingly powerful amplifier needed.

Our smart solution was changing the number of turns, something never done before on the market. Taking into account the right conditions, the varying turns will generate the proper field requested for the essay. This solutions offers a perfectly suitable system to perform the EN 50617-2 standard essay.

Our added value

  • Search of an alternative method: using Helmholtz coils instead of a single coil is a pioneering solution optimising the standard suggestions
  • The Helmholtz coils with a configurable turns number can adapt to an incredibly wide range of frequencies, something not seen before on the market
  • Creating an adaptated network capable of running the system in this bandwidth so that with a small amplifier the whole system can be practically covered
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