RS4 Codici is a train protection system employed in Italy. The name is an acronym for the Italian name Ripetizione Segnali a 4 codici what is called in German signal repeating system with 4 terms.
The system transmits the position of the next in the direction signal to the cab of the engine vehicle. The device helps the driver to safely recognize the signals even in poor visibility conditions or at signal locations in curves.
RS4 Codici consists of the following parts:
- Two receiver coils on the rails in front of the first axis of the traction vehicle or the control vehicle
- An electronic rack to decode the received signals
- A braking action group
- A display and control device in each cab
In the rails, an alternating current flow at a frequency of 50 Hz, which is modulated with a frequency dependent on the position signal:
A change in the code, this must be acknowledged by the driver with the RIC button within 3 seconds, otherwise on the brake active group rapid braking is triggered.
A further development of RS4 Codici represents BACC