AISY: Ground loops
The ground loops are made of stranded copper cables,
cross-section 2.5 mm².
Their shape is application dependant:
Basic selective detection : “O” shape, 2 turns
Selective and inductive detection : “8” shape, 2 to 3 turns
In case of controls for railroad switch, transmission and reception loops can be separated, in order to optimize very low vehicle speed operation.
In this case, the two loops have a “O” shape, except that, on the axis of incoming vehicle, the reception loop is in “advance” from the transmission loop, by say 30 cm.
Loop dimensions also are application dependant:
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In length: say 0.5 meter per 10 km/h speed, normal data exchange. As so, a 3 meter loop accepts vehicle speed up to 60 km/h. -
In width: from 0.35 meter (tramway APS application) up to 9 meters (loop covering up to 3 lanes for buses applications).
Selective
Selective en inductive
Implementation
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Loops for buses are directly placed in the road surface, at say 3 cm depth, by sawing the road finish surface.
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Tramway loops are made in rigid tubular structure.
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The loops are connected to the electronics through a shielded multiple twisted pair cable, with a cross-section of 0.75 mm³.
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Connection between the loops terminals and the cable is made through a Scotch 3M muff.
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The loops can be placed as far as 500 meters from the electronics. In this latter case, multiple pairs (up to 3) are connected in parallel in order to reduce the cable impedance.
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The tramway loops can be buried up to 17 cm below the rail rolling level.
