Continuous Automatic Warning System

The Continuous Automatic Warning System ( CAWS abbreviation ) is used together of ATP on the routes of Iarnród Éireann in Ireland to train safety. The system consists of coded track circuits and on-board equipment. The transmission of the code via coils which are mounted on front of train on each rail.

The carrier frequency of 50 Hz is modulated by pulsed square wave codes corresponding to the signal aspect. For the maintenance aspect, no code is generated. The system is thus fail-safe, because a loss of code is displayed as the maintenance aspect.

• Codes 50, 120 and 180 cycles per minute
• Translation by CAWS as yellow, double yellow and green

In the electrified area around Dublin (DART ) has a different carrier frequency of 83.3 Hz is used to avoid interference from the 50 Hz power supply. The number of codes is greater because they also control the Automatic Train Protection ( ATP) of the vehicles for the DART area.

• Codes 50, 75, 120, 180, 270 and 420 cycles per minute
• Translation by CAWS as yellow, green, yellow, green, double yellow and green
• Translation by DART ATP as 29 km / h, 30 km / h and 50 km / h, 50 km / h and 75 km / h and 100 km / h speed limit.

The driver of diesel units will need to select the appropriate carrier frequency when they enter and leave in an electrified area.

Benefits

Because CAWS is a continuous system, a signal aspect can be upgraded anywhere between two signals. The driver can then accelerate with the knowledge that the signal before it a favorable aspect shows (traveling at a higher speed ), although it is not yet in sight. Likewise, the driver quickly react to an unexpected devaluation (traveling at a slower speed, stop) signal aspect.

Disadvantages

Because CAWS based on track circuits, it can not be used in areas where axle counters are used. CAWS does not respond when a signal was passed to a stop position when the driver has confirmed this signal aspect.

• Transport (Ireland )
• Command