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Speed Control Photos

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Speed Control Photos

An example of how the driver sees speed control signals operating.

Fig.1: The Approach to Acton Town.

Acton Home Sigs1.jpg (46507 bytes)

This is the driver's view of the eastbound approach to Acton Town (Piccadilly Line) when coming from Ealing Common.  He is shown four red signals indicating that the platform ahead is occupied.  The first signal will be cleared if the driver controls the train so that its speed is detected as being low enough to enable a stop at the second signal. 

The short section of "current rail" on the right hand side is the instantaneous speed detector.  This contains a series of electro-magnetic coils of alternating polarity, mounted on a magnetic base plate, which are activated as the trains current collector shoe passes over it.  As the shoe passes, an alternating current is generated with a frequency proportional to the speed of the train.  This is passed through a frequency filter and, if within the correct range, a relay is activated to clear the signal.  Photo by Tube Troll.

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Fig.2: The Signal Clearing Sequence

Acton Home Sigs2.jpg (62649 bytes)

In this second photo, the driver has reduced the speed of the train, the first, speed controlled signal has cleared and the train is now approaching the next signal.  This signal has also cleared to green because the train in the platform has started to leave.  The remaining signals will now clear in sequence.  Photo by Tube Troll.


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