Anuncio de Señales y Frenado Automático

Anuncio de Señales y Frenado Automático ("Automatic Braking and Announcement of Signals" in English) is an Automatic Warning System widely deployed on the Spanish rail network. It consists of a mechanism that stops a train if the driver does not properly heed signals.

ASFA is a directive of the Westcab intermittent train control technology commercialized by WABCO's Italian subsidiary and licensed to Dimetal of Spain for use on various Iberian rail systems. RENFE, the Spanish state-owned railway operator, was put in charge of the rail system in 1975. Before this, the rail networks of other countries had previously deployed similar systems which gave ASFA a technological advantage over its competitors.

It was progressively rolled out on all of the lines belonging to RENFE beginning with the principal lines and extending to practically the entire Spanish rail network totaling over 13,000 km of track, leaving few lines without ASFA installed. It is also widely deployed on narrow gauge railways belonging to FEVE and Ferrocarrils de la Generalitat Valenciana.

In 2005 Adif, the state-owned Administrator of Rail Infrastructure, began a systemic renewal process which would become known as "ASFA Digital". The changes in the new system do not affect the beacons, which continue to transmit their information in analogue form, but rather just the signal processing equipment in the train which once digitalised will allow for the use of braking curves or a better representation of the received signals in the cabin.

ASFA makes use of inductive coupling between a transceiver on the rolling stock and a tuned "beacon" that oscillates at one of 9 preset frequencies when activated by a magnetic field emanating from said transceiver. The beacon requires no external power, however, there is a cable for controlling small relays inside the transponder which switch capacitors in/out of the coil circuit and determine which frequency is detected by the passing train. The nine frequencies lie in the 60-100 kHz range (although only five frequencies are used in ASFA) and the wayside beacons are mounted between the rails offset from the track centerline to provide directionality. Each beacon is protected from debris strikes by a wooden ramp on each side and are typically placed at distances of about 5 and 300 meters before a signal.

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Wikipedia