Bi-directional Operation
Because the permanent magnet is located in the centre of the track, it operates in both directions. The permanent magnet can be suppressed by an electric coil of suitable strength.
Where signals applying to opposing directions of travel on the same line are suitably positioned relative to each other, a common magnet may be used, comprising an unsuppressed permanent magnet associated with both signals' electro-magnets.
Read more about this topic: Automatic Warning System
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