Railway switches and signals – Block-signal systems – Automatic
Patent
1984-11-09
1988-01-19
Caldwell, Sr., John W.
Railway switches and signals
Block-signal systems
Automatic
246 63R, 246167R, B61L 320
Patent
active
047200677
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of increasing the number of differentiated signals that can be sent from a base station equipped with a coder to a rail vehicle, fitted with a decoder, that is located on a section of track connected to the said base station, and to a method for transmitting signals from at least two base stations, each provided with a coder, to two different railroad vehicles located on two different sections of track that are connected each to one of said base stations, said rail vehicles being provided each with a decoder and being capable of moving on both sections of track, the signals being sent separately from each other and being intermingled at least in part both with regard to time.
It is known that signals can be sent inductively from a base station to a locomotive located on a section of track by using pulse frequency modulation. To this end, the section of track is generally made up of two rails that are insulated from each other. These two rails are terminated at the start and the end of a block in each instance by a special transformer. In general, conventional systems transmit four different items of information by pulse frequency modulation at different levels. However, the introduction of high-speed railroad systems necessitates the transmission of more information than was formerly the case. For this reason, it has already been proposed that the number of installations be doubled, and that a second alternating current frequency be employed for the transmission of additional information. However, a system of this kind entails prohibitive costs.
It is a task of the present invention to provide a method that will permit an increase in the number of signals that can be transmitted from a base station to a railroad vehicle, using additional, simple means and, above all else, without any substantial modification of existing systems.
According to the present invention this task has been solved by a method of the kind described in the introduction hereto, in by effecting said transmission both by a pulse frequency modulated carrier and simultaneously by a pulse width modulated carrier.
In order to effect transmission by technical means available today it is advantageous if an electrical alternating current is used as a carrier, transmission being effected inductively.
If the signals are transmitted by alternating current pulses of different durations, the pulses containing several half-waves and alternating with spaces between pulses of different lengths, then in order to provide for the simultaneous transmission of two sets of information the frequency of the pulse frequency modulation should be determined by the time width of the alternating current pulses and by the time width of the current pauses. The pulse width should be determined exclusively by the width of the alternating current pulse.
In order to ensure that no modifications to existing equipment are required and that existing coders can process the signal generated using existing methods, it is advantageous that the width of the alternating current pulse for pulse width modulation is within the existing range of the frequency modulated alternating current pulse.
In order to ensure reliable differentiation of the pulse lengths, it is advantageous if the time widths of the alternating current pulses and of the pauses correspond to integer, preferably even-number, multiples of the alternating current half-wave time.
In order to permit pulses that are sharply defined in relation to pulse length, at the pulse length provided by the present systems it is desirable that the current pulse switches on an alternating current source at the voltage zero-crossing point and switches this source off at the current zero-crossing point.
Particularly reliable switching is provided when the zero axis is crossed if the alternating current source is switched electronically.
Furthermore, in order to provide for reliable acquisition of the pulses it is preferable that the decoding be carried out electronically.
It is also advantag
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"Cab Signalling on the New Tokaidoline", The Railway Gazette, vol. v56-123, No. 18, Sep. 1967, London (GB), pp. 701-704.
Goldberg and Bath, "Multiplex Employing Pulse-Time and Pulse-Frequency Modulation", Proceedings of the Institute of Radio Engineers, vol. 37, No. 1, Jan. 1949.
Caldwell Sr. John W.
Oberley Alvin
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