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Fault tolerant apparatus for detecting the passage of a moving body

  • US 5,889,478 A
  • Filed: 03/31/1997
  • Issued: 03/30/1999
  • Est. Priority Date: 04/01/1996
  • Status: Expired due to Term
First Claim
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1. Apparatus for detecting the passage of a moving body at a determined point in its guided displacement along a track, the apparatus comprising, on the moving body, an active interrogation assembly connectable to an electrical power supply, and on the track, a passive responder, wherein:

  • the interrogation assembly has a low frequency transmitter and a medium frequency transmitter that continuously operates while the moving body is moving, each having a respective antenna directed to transmit towards a predetermined zone with respect to the moving body and selected to be traversed by the responder during displacement of the moving body; and

    the responder comprises a low frequency signal receiver circuit and a medium frequency signal receiver circuit having respective tuned radiating circuits associated in such a manner that a low frequency signal induced in the low frequency circuit by passage through the zone causes the medium frequency radiating circuit of the responder to be closed at the rate of the low frequency, with the interrogation assembly also having means responsive to disturbances in the medium frequency transmitter caused by closing the medium frequency tuned radiating circuit of the responder when the responder is in said zone;

    wherein said medium frequency circuit of the responder includes at least two assemblies having respective tuned radiating circuits that are strongly coupled together and each connected to a respective one or two logic units that arranged to deliver a digital message and causes the medium frequency radiating circuit to be closed only for bits of a determined value in the digital message, the digital messages originating from one of the logic unit being different from the digital message originating from the other and being transmitted asynchronously; and

    said low frequency signal receiver circuit includes a plurality of tuned radiating circuits connected in series that are spaced apart in the displacement direction of the moving body and that are provided with means for closing them simultaneously at the rate of the message originating from the associated logic unit.

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