Railroad grade crossing protection system

Claim 2

In a system for deriving from railroad tracks of low ballast information for predicting the time required for arrival at a given location of a distant train which is moving on said track towards said location, comprising: means for applying an AC signal of a constant current level on said track from said location; means for deriving a first voltage proportional to the reactance component across said tracks said first voltage having an output vs. train distance curve approaching substantially zero slope in the vicinity of a first train distance from said location; means for deriving a second voltage proportional to the impedance component across said tracks having a time rate of change indicative of the speed of said train approaching said location, said second voltage having an output vs. train distance curve of a slope substantially greater than zero over a train distance greater than said first train distance; said first voltage being indicative of the distance of said train from said location over said greater train distance and being substantially free from the effect of lumped resistance in said track; means for differentiating said second voltage to obtain a voltage representative of the instantaneous speed of said train at any train position over said greater train distance; and means for combining said first voltage and said differentiated voltage to provide a third voltage which is a function of the time required for said train to arrive at said given location from any train position over said greater train distance.

Claim 3

The system as defined in claim 1 and further comprising means for utilizing said third voltage for operating a warning device at said location.

Claim 4

The system as defined in claim 1 wherein said means for deriving said first voltage is a quadrature detector.

Claim 5

The system as defined in claim 1 wherein said means for deriving said second voltage is an amplitude detector.

Claim 6

The system as defined in claim 1 wherein said means for differentiating is an operational amplifier differentiator.

Claim 7

The system as defined in claim 1 and further comprising: means for providing a reference voltage; and comparator means responsive to said reference voltage and said third voltage provided by said combining means, said comparator means being adapted to provide an output when said third voltage exceeds said reference voltage.

Claim 8

The system as defined in claim 6 and further comprising means for utilizing the output voltage of said comparator means for operating a warning device at said location.

Claim 9

In a system for predicting the time of arrival of a train on a track comprising: a source of AC signals at a constant current level, said source being coupled across said tracks at a selected location; a quadrature detector being coupled to receive signals from said track at said selected location, said quadrature detector being adapted to proVide a first output voltage proportional to the reactance component across said track and having an output vs. train distance curve approaching substantially zero slope in the vicinity of a first train distance from said location; an amplitude detector being coupled to receive signals from said track at said selected location and to provide a second output voltage proportional to the impedance component across said tracks, said second output voltage having an output vs. train distance curve of a slope substantially greater than zero over a train distance greater than said first train distance, said first output voltage being indicative of the distance of said train from said selected location over said greater train distance and being substantially free from the effect of resistance variations in said tracks; a differentiator circuit being coupled to said amplitude detector, and being responsive to said second output voltage of said amplitude detector for providing a third output voltage indicative of the instantaneous speed of said train at any position over said greater train distance, and a summing amplifier being coupled to said amplitude detector and to said differentiator circuit and being responsive to said third output voltage of said differentiator circuit and said first output voltage of said quadrature detector, said summing amplifier being adapted to provide a fourth output voltage which is a function of the time required for said train to arrive at said location from any train position over said greater train distance.

Claim 10

In a system for predicting the time of arrival of a train on a track comprising: a source of AC signals at a constant current level, said source being coupled across said tracks at a selected location; a quadrature detector being coupled to receive signals from said track at said selected location, said quadrature detector being adapted to proVide a first output voltage proportional to the reactance component across said track and having an output vs. train distance curve approaching substantially zero slope in the vicinity of a first train distance from said location; an amplitude detector being coupled to receive signals from said track at said selected location and to provide a second output voltage proportional to the impedance component across said tracks, said second output voltage having an output vs. train distance curve of a slope substantially greater than zero over a train distance greater than said first train distance, said first output voltage being indicative of the distance of said train from said selected location over said greater train distance and being substantially free from the effect of resistance variations in said tracks; a differentiator circuit being coupled to said amplitude detector, and being responsive to said second output voltage of said amplitude detector for providing a third output voltage indicative of the instantaneous speed of said train at any position over said greater train distance, and a summing amplifier being coupled to said amplitude detector and to said differentiator circuit and being responsive to said third output voltage of said differentiator circuit and said first output voltage of said quadrature detector, said summing amplifier being adapted to provide a fourth output voltage which is a function of the time required for said train to arrive at said location from any train position over said greater train distance.

Claim 11

The system as defined in claim 8 and further comprising means coupled to said summing amplifier and to a warning device for utilizing said fourth output voltage of said summing amplifier for operating a warning device at said location.

Claim 12

The system as defined in claim 8 and further comprising: a reference voltage source adapted to provide an output voltage of a predetermined level; and an amplitude comparator being coupled to said summing amplifier and said reference voltage source and being responsive to said fourth output voltage of the said summing amplifier and to the output voltage of said reference voltage source and being adapted to provide an output signal when the voltage provided by said summing amplifier exceeds the voltage provided by said reference voltage source.

Claim 13

The system as defined in claim 8 wherein said source of AC signals includes: an oscillator adapted to provide an output signal at a predetermined frequency; and a power amplifier coupled between said oscillator and said tracks.

Claim 14

The system as defined in claim 11 and further including a band-pass amplifier coupled between said track and said quadrature detector and said amplitude detector.

Claim 15

The system as defined in claim 12 and further comprising means coupled to said amplitude comparator for utilizing the output voltage of said amplitude comparator for operating a warning device on said location.