Continuous Automatic Warning System
The Continuous Automatic Warning System (abbreviation CAWS) is used jointly by the ATP on the Iarnród Éireann routes in Ireland for train protection. The system consists of coded track circuits and on-board devices. The codes are transmitted via coils that are mounted on the front of the train above each rail .
The 50 Hz carrier frequency is modulated with pulsed square wave codes according to the signal aspect. No code is generated for the stop aspect. The system is thus fail-safe because a code loss is displayed as a halt 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 ), a different carrier frequency of 83.3 Hz is used to avoid interference from the 50 Hz supply voltage . 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, 50 km / h, 50 km / h, 75 km / h and 100 km / h speed limit.
The driver of the diesel units must select the appropriate carrier frequency when they turn into an electrified area or extend.
advantages
Because CAWS is a continuous system, a signal aspect can be upgraded anywhere between two signals. The driver can then accelerate knowing that the signal in front of him shows a more favorable aspect (travel at higher speed), although it is not yet in sight. Likewise, the driver can react quickly to an unexpected devaluation (travel at lower speed, stop) of the signal aspect.
disadvantage
Because CAWS is based on track circuits, it cannot be used in areas where axle counters are used. CAWS does not react if a signal has been passed in the stop position if the driver has confirmed this signal aspect.