Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
164 words
A DC track circuit sensitive to current variations comprising: a quasi-DC pulse source of current coupled to a pair of track rails, a current sensitive receiver coupled to said pair of track rails, said current sensitive receiver comprising: a toroidal core with an air gap, said core coupled to said track rails via a single conductor, a Hall sensor located in said air gap to sense a magnetic field induced in said core by current coupled from said track rails, operational amplifier means for amplifying a signal emitted by said Hall sensor, and level detector means coupled to said operational amplifier means to emit a distinctive signal in the event that an input to said level detector means exceeds a threshold established at said level detector means, whereby changes in current level in said track rail produce distinctive outputs from said level detector means as said signal emitted by said Hall sensor varies above and below the threshold established by said level detector means.
Claim 2
Dependent Claim
164 words
A DC track circuit sensitive to current variations comprising: a quasi-DC pulse source of current coupled to a pair of track rails, a current sensitive receiver coupled to said pair of track rails, said current sensitive receiver comprising: a toroidal core with an air gap, said core coupled to said track rails via a single conductor, a Hall sensor located in said air gap to sense a magnetic field induced in said core by current coupled from said track rails, operational amplifier means for amplifying a signal emitted by said Hall sensor, and level detector means coupled to said operational amplifier means to emit a distinctive signal in the event that an input to said level detector means exceeds a threshold established at said level detector means, whereby changes in current level in said track rail produce distinctive outputs from said level detector means as said signal emitted by said Hall sensor varies above and below the threshold established by said level detector means.
Claim 3
Dependent Claim
101 words
The DC track circuit of claim 1 in which said pulse source is connected across said pair of track rails at a first location, said current sensitive receiver is coupled across said pair of track rails at a second location, spaced along said track rails from said first location, whereby decreases in current level in said single conductor produce a distinctive output from said level detector means as said signal emitted by said Hall sensor decreases below a threshold established by said level detector means to thereby indicate occupancy of a section of track defined between said first and second location.
Claim 4
Dependent Claim
58 words
The apparatus of claim 2 which further includes at least a second conductor magnetically coupled to said toroidal core and coupled to a switched source of voltage, wherein said level detector means comprises a first level detector and a second level detector, said first level detector having a threshold different from a threshold of said second level detector.
Claim 5
Dependent Claim
29 words
The apparatus of claim 3 wherein said first level detector is a vital level detector and has a threshold about 50% of a threshold of said second level detector.
Claim 6
Dependent Claim
158 words
The apparatus of claim 2 which further includes: a second and third conductor each magnetically coupled to said toroid in opposite senses, a pair of switches, each connecting one of said second and third conductors to a potential source, and wherein said operational amplifier means includes first channel means for amplifying signals of one polarity and second channel means for amplifying signals of an opposite polarity, said level detector means includes two pairs of level detectors, a first pair coupled to said first channel means and a second pair coupled to said second channel means, each pair of level detectors including a single vital level detector with threshold below the threshold of the other level detector of said pair, whereby lack of occupancy is indicated by pairs of level detectors tripping and safe operation is checked by closing first one and then the other of said pair of switches and noting the tripping pattern of said level detectors.
Claim 7
Dependent Claim
51 words
The apparatus of claim 5 wherein said potential source, number of turns of said second and third conductors and thresholds of said level detectors is selected to ensure that one and not the other level detector of each pair is tripped in response to energization of said second and third conductors.
Claim 8
Dependent Claim
68 words
The apparatus of claim 1 wherein said pulse source and current sensitive receiver are coupled in series across a pair of track rails whereby increases in current level in said track rail produce a distinctive output from said level detector means as a signal emitted by said Hall sensor varies above the threshold established by said level detector means to indicate a vehicle approaching said source and receiver.