Device for the detection of the passage of a vehicle using a passive transponder.

摘要

The device comprises an interrogation unit and a passive transponder, the one associated with the vehicle and the other with the track. The interrogation unit (10) has on the one hand a low-frequency transmitter (26) and a middle-frequency transmitter (16) operating continuously, having respective antennas transmitting to an area specified in relation to the antennas and through which the transponder crosses during the motion, and on the other hand an element responsive to the characteristics of the transponder when the latter is inside the area. The transponder comprises a circuit for receiving the low-frequency signal provided for controlling a middle-frequency circuit. The LF and MF circuits have respective tuned radiating circuits associated in such a way that the low-frequency signal induced in the low-frequency circuit causes the short-circuiting of the middle-frequency resonant circuit of the transponder, in tempo with the low frequency. <IMAGE>