Keywords: signalling equipment, vibrations, shocks, testing, signal processing, railway standards.

Standards in force [1,2] define the vibration tests to be performed on signalling equipment for homologation or acceptance. It is unfortunately a common experience to find out that a non negligible number of equipment failures in service arise from unforeseen and unexpectedly high vibration levels. Signalling equipment directly fastened to rails and to sleepers is prone to failure that, although preserving the safety of passengers, induces large disruptions in traffic schedules.

The equipment considered in this paper is a rail-mounted treadle (wheel detector) which exhibits a root cause for failures, i.e. too strong vibrations, which is common to a number of different signalling equipment.

The paper describes the outcomes of a complex test programme (including measurements of treadle vibrations, rail vibrations, track vertical deflection measurements, vertical track decay rate estimation and rail roughness compared to those found in a "standard track" section) which shows how local conditions may affect life of such equipment.

The identification of spurious peaks in pass-by signals by using the kurtosis function allows the identification of unfavourable local conditions due to installation or unevenly worn wheels (wheel flats). While vibrations in the "standard track" were rather low due to the good surface quality of the rails, the stresses of the wheel detectors installed in proximity of aluminothermic welds and insulated joints are dominated by a series of shocks also for rolling stock with "round" wheels (no wheel flats or other defects detectable).

While vertical deflections identify the track as "in good conditions" for a conventional line, the estimated vertical rack decay rate showed poor track damping properties. The latter is one of the fundamental parameters to identify the minimum distance of signalling equipment from a weld or a joint, as a lower track decay rate results in higher acceleration values far from local discontinuities. High rail vibration and shocks, together with the high transmissibility of vibrations along the rail, are in fact the likely reason for the failures observed on the wheel detectors measured in the present work.

It is concluded that standards for type tests should better consider the conditions found in service about the geometry of welds and track properties (vertical decay rate and roughness) to define the minimum distance from welds and insulated rail joints.

An attempt was made to count the number of shocks starting from the simultaneous use of RMS and kurtosis data, nevertheless the proposed algorithm needs to be validated by further work.

1

EN 50125-3, "Railway applications - Environmental conditions for equipment. Part 3: Equipment for signalling and telecommunications", 2004.

2

Rete Ferroviaria Italiana, "Prove di Tipo e di Accettazione per le apparecchiature elettroniche ed elettromeccaniche destinate agli Impianti di Sicurezza e Segnalamento", Specifica Tecnica IS 402, 2000.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £130 +P&P)