Most light signals are provided with a crocodile. It makes a phusical contact with a passing train, hence transfering the signal's state to the driver's cabin.
Each train carry in the bogie a brush that makes a physical contact with the crocodile. The crocodile can carry a positive or negative voltage (15V) depending on the signal status.
When the trainengineer passes a green signal (proceed at line speed), the crocodile carries +15V. A bell will ring in the driver's cabin.
When the trainengineer passes a yellow signal then:
1) By old trains a pneumatic piston will fall, which the driver has to push back in the original position within 30 seconds.
2) By new types, the trainengineer can confirm the signal just before or after passing the signal by pushing at a button.
He must repeat the action for every double yellow, green yellow horizontal and green yellow vertical signal. When the trainengineer doesn't respond within 30 seconds an emergency brake will energise.
A red signal will not be transferred to the cabin.
The crocodile can carry a negative (-15V) voltage when the signal is green and a positive (+15V) when the signal is yellow. When the signal is red the voltage over the crocodile is 0V. When the trainengineer passes a red signal, there is nothing that stops this train.
There are several reasons:
Signals in the opposite directions are red, the train moving in one directions will
also notice the signals standing in the opposite direction, but because the crocodile
voltage is 0V, the train doesn't react to them
Crocodiles that protect signals don't work for trains proceeding in the other direction.The crocodiles are
|The trainengineer must confirm the signal|
|The crocodile is not working for this train|
|The trainengineer must confirm only the double yellow signal|
In the Belgian network there are several test crocodiles. The' re placed lower than the normal crocodiles and they are used to test the depth of the brush under the train. When the trainengineer doesn't receive a signal in the cabin, the brush is worn out. The engineer must report it at the next locomotive service point. These test crocodile are signaled with
On the lines fit out with signals in both ways, the temporary
speed announcement signs have on there back a sign "crocodile". This sign
indicates that the crocodile conform to signals for the other direction
The driver may neglect this crocodile.
The signal is placed before the main signals when the visibility is poor. The light bar is steady or flashing according to the main signal that's steady or flashing.
The main signal commands stop or proceed with a speed execution
The main signal is clear
Not available yet.
The signal is placed on most platforms. The stationmaster can serve this signal when all passengers are boarded and the train is ready to leave the station.
>> after 7 sec. >>
All signals are announced by countdown markers.
But mostly, and than I mean 95% of the signals are announced with only two markers. The markers of the opposite track are different.
When the signal can not give a "stop", the last marker doesn't have an extra dot.
When the main signal doesn't have a distant signal the markers are different.
When the reference speed is less than 40km/h
When the reference speed is between 40 and 60km/h
When the reference speed is more than 60km/h
There must a distant signal