Frame levers

We have in our signal box a 23-lever London Underground frame that came out of service from Hyde Park Corner.

Although the mechanical interlocking has been removed, we retain the electromechanical locking by the use of solenoids on each of the bars. This allows the system to lock levers in a manner similar to that which mechanical interlocking would provide.

Each lever has two inputs and a single output. The inputs read when the levers are all the way in the frame (normal), and when they are all the way out of the frame (reverse). The use of two inputs means that the system can detect when a lever is not fully either out of or in the frame. The output is used to lock the lever in the event that it should not be pulled (for example to protect pointwork).