Compliance with Interoperability Directive for Axle Counters

Leedeo Engineering has developed a low-cost pre-certification system for the verification of electromagnetic compatibility requirements of the European Railway Agency document ERA-ERTMS-033281, for axle counter systems.

The challenge of this system lies in the absence of a normative reference document where this test is defined. The text taken as a reference, as it is the closest to the description of an immunity test, is Annex C of UNE-EN 50617-2 standard. The system proposed in this document has several disadvantages in its practical implementation.

Firstly, it is based on field generation with a single loop antenna. Secondly, calibration must be carried out in the presence of the rail, which significantly affects the magnetic field generation capacity, especially in one of its spatial orientations.

The system proposed and developed by Leedeo Engineering consists of the use of Helmholtz coils since it has a much higher performance in generating magnetic field from the same circulating intensity than a system based on a single loop antenna. The magnetic field is always proportional to the intensity circulating on the loop antenna. On the other hand, the uniformity of the field created is defined, in a loop antenna, only in the infinitesimal plane of the antenna itself. This will decrease strongly regarding distance, as we move away from central plane. However, the great advantage of a configuration based on Helmholtz coils is that the field is uniform in a volume between the two coils.

Axle counters occupy a volume in space and usually consist of two detectors separated by a certain distance in order to determine the direction of passage of the train. Consequently, such counters cannot be considered infinitesimal. Since the magnetic field created by a single coil is strongly dependent on the distance to the centre of the coil, the actual field controlling a real system may differ significantly from the field calibrated with a single coil. However, by carefully choosing the parameters of the Helmholtz coils, a uniform volume can be achieved. This will cover all or most of the detector system to be tested. The whole system will be under the same degree of perturbation. In addition, the coil system designed by Leedeo allows you to vary the settings without making any physical changes, via an intelligent configuration system.

Handling a highly inductive load like magnetic field generating coils and with a wide spectrum to cover is not easy. It was originally designed to cover the lower working band and reach the middle band with a low cost 4 quadrant amplifier. The low cost of the initial system is limited by the high part of the frequency band, but it has allowed Leedeo to work and optimize the necessary impedance matching system. Subsequent tests have shown that using a low power RF amplifier allows to cover the whole range, with sufficient levels to cover the most demanding requirements of the document ERA-ERTMS-033281 version 4.0.

As described in the CLC/TS 50238-3 standard, one of the two monitoring antennas has also been manufactured with a negligible deviation from professional antennas in almost all bands. It has only one deviation that can be corrected at 10 kHz. Nevertheless, instead there is a system for monitoring the current circulating through coils. This allows measuring the real field by applying a factor that depends on whether the rail is there or not.

At Leedeo Engineering, we are specialists in the development of RAMS and Interoperability Railway projects, applying Interoperability Directives, CENELEC standards EN 50126, EN 50129, EN 50128, EU Implementation Regulation 402/2013 with the application of the Common Safety Methods CSM-RA.