Patent GB-929527-A (GB)
Title: An inductive communication system
IPC: B61L25/04
Filed: 1961-05-02
Abstract: 929,527. Controlled non-linear inductors. SIEMENS & HALSKE A.G. May 2, 1961 [May 2, 1960], No. 15941/61. Class 40 (9). [Also in Groups XXX and XL (c)] In an interrogator-responder system for coded vehicles moving on a predetermined track, magnetic memory cores are provided in the transponders attached to the vehicles and are adjusted initially in accordance with the vehicle identification code by A.C. signals transmitted from a priming station adjoining the track and rectified in the transponder. The energy of the received priming, interrogation, or erasing signals is used to power and control the transponders. As shown in Fig. 1, each transponder KA contains eight resonant circuits R1 to R8 tuned to frequencies f1 to f8 respectively and connected to respective windings W1 to W8 of transfluxors T1 to T8. Initially, all the transfluxors are magnetized so that the output windings W1 to W8 present a high impedance and the resonant circuits R1 to R8 are unaffected. For coding purposes four out of the eight resonant circuits are detuned. At the encoding or priming station KJ a coding unit C is adjusted to pass four of the frequencies f1 to f8 from generators J1 to J8 to a modulator MJ so that the carrier frequency fi from a generator J is modulated with the corresponding frequencies. As the vehicle passes, the modulated signal is transmitted inductively to the transponder loop EJ and is demodulated at DJ. The four frequencies are passed by corresponding filters M1 to M8 and after rectification are supplied to corresponding windings B1 to B8 of the transfluxors T1 &c., thus causing four of the transfluxors to be blocked and the corresponding windings W1 &c. to present a low impedance virtually short-circuiting four of the resonant circuits R1 &c. At the interrogation point, the interrogator KF provides frequencies f1 to f8 from generators F1 to F8 which continuously modulate a carrier ff from a generator F. The modulated signal is received inductively by a passing vehicle and after demodulation at DF the carrier ff is rectified at GF and supplies power for the responder oscillator A. The modulation frequencies are supplied to the chain of resonant circuits R1 &c., but only those frequencies are passed to modulate the oscillator A which correspond to the shortcircuited resonant circuits. The reply signal consisting of a carrier frequency fa modulated by the four selected frequencies is received by the interrogator receiver circuit EA and after demodulation is fed to filters El to E8, the resulting signal being either recorded or used to establish the subsequent route of the vehicle. The vehicle may be interrogated any number of times until it reaches the erase unit KL where a frequency fL is supplied by a generator L and supplied to the circuit EL of the transponder. After rectification at GL, windings S1 to S8 of the transfluxors are energized, thus returning the transfluxors to their initial state. In a modification, Fig. 2, the priming unit KJ continuously transmits a frequency fi from a generator J via circuit SJ and the circuit S transmits four of the frequencies f1 to f8 as selected by a coding unit C in sequence through a continuously rotating switch ZJ. Initially, the transfluxors T1 to T8 'are in the unblocked condition. The frequency fi is selected by a resonant circuit RJ and rectified at GJ to supply a potential unblocking the emittercollector circuit of the transistor Tr. The other four received frequencies are selected by appropriate circuits R1 to R8 and after rectification energize corresponding inhibit windings B1 to B8 to block four of the transfluxors. At the interrogator KF frequencies f1 to f8 are transmitted in sequence by a switch ZF, but frequency fi is not transmitted so that transistor Tr remains blocked. Only the unblocked transfluxors will pass the corresponding received frequencies via windings W1, A1, &c., and each frequency passed will cause a generator A, which is powered by a portion of the incoming signal rectified at G, to oscillate at a frequency fa. The receiver circuit EA receives the frequency fa when transmitted and the receiver output is passed via a switch ZA, synchronized with the switch ZF, to a code convertor U. Erasure of the code takes place at KL as in Fig. 1. In an alternative arrangement, Fig. 4 (not shown), a shift register in the transponder selects the appropriate magnetic storage devices for the identification code, or alternatively a counter may be used, Fig. 5 (not shown).