Failure detection for highway grade crossing signal systems

Claim 2

A highway crossing signal system, for controlling highway warning signals where the highway is intersected by a stretch of railroad track, comprising in combination, a. an overlay track circuit, for detecting a train approaching the highway within an approach warning section requiring a warning to highway traffic, comprising, 1. a transmitter means connected to the rails at the distant end of the approach section and operable for supplying output signals to said rails, 2. a receiver means connected to the rails at said crossing on the opposite side of said highway from said transmitter means for receiving signals therefrom through the rails of said approach section when unoccupied by a train; b. an advance detection means for detecting a train when in approach to said approach warning track section, c. a modulation source connected to said transmitter means and controlled by said advance detection means for modulating the transmitter output signals by a first or second characteristic as a train is or is not detected, respectively, by said advance detection means, d. a demodulation means coupled to said receiver means for detecting the reception of said first or second modulation characteristic, e. a protection control means normally controlled by said track circuit and responsive to the detection of a train within said approach warning section for activating said warning signals to warn highway traffic of the approaching train, f. a testing means controlled by said demodulation means and coupled to said protection control means when an approaching train is detected only by said advance detection means for simulating the passage of a train through said approach warning section and for monitoring the operation of said protection control means to simulate the proper activation of said warning signals in response to the simulated passage of a train, and g. a failure warning means controlled by said testing means for registering a fault condition when an improper operation of said protection control means is detected during a simulated train passage test period, 1. said failure warning means operable for displaying an indication to highway traffic that an unsafe condition exists when a fault condition in said protection control means is registered, 2. said failure warning means also coupled for inhibiting further operation of said protection control means in response to the detection of a train by said track circuit when a fault condition exists.

Claim 3

A highway crossing signal system as defined in claim 1, for a stretch of track over which trains move in either direction, further comprising, a. a track circuit for each direction of travel for separately detecting a train occupying the corresponding approach warning track section, each track circuit including,

Claim 4

said failure warning means also coupled for inhibiting further operation of said protection control means in response to the detection of a train by said track circuit when a fault condition exists.

Claim 5

said failure warning means also coupled for inhibiting further operation of said protection control means in response to the detection of a train by said track circuit when a fault condition exists.

Claim 6

a receiver means connected to the rails at said crossing on the opposite side of said highway from said transmitter means for receiving signals therefrom through the rails of said approach section when unoccupied by a train; b. an advance detection means for detecting a train when in approach to said approach warning track section, c. a modulation source connected to said transmitter means and controlled by said advance detection means for modulating the transmitter output signals by a first or second characteristic as a train is or is not detected, respectively, by said advance detection means, d. a demodulation means coupled to said receiver means for detecting the reception of said first or second modulation characteristic, e. a protection control means normally controlled by said track circuit and responsive to the detection of a train within said approach warning section for activating said warning signals to warn highway traffic of the approaching train, f. a testing means controlled by said demodulation means and coupled to said protection control means when an approaching train is detected only by said advance detection means for simulating the passage of a train through said approach warning section and for monitoring the operation of said protection control means to simulate the proper activation of said warning signals in response to the simulated passage of a train, and g. a failure warning means controlled by said testing means for registering a fault condition when an improper operation of said protection control means is detected during a simulated train passage test period,

Claim 7

a receiver means connected to the rails at said crossing on the opposite side of said highway from said transmitter means for receiving signals therefrom through the rails of said approach section when unoccupied by a train; b. an advance detection means for detecting a train when in approach to said approach warning track section, c. a modulation source connected to said transmitter means and controlled by said advance detection means for modulating the transmitter output signals by a first or second characteristic as a train is or is not detected, respectively, by said advance detection means, d. a demodulation means coupled to said receiver means for detecting the reception of said first or second modulation characteristic, e. a protection control means normally controlled by said track circuit and responsive to the detection of a train within said approach warning section for activating said warning signals to warn highway traffic of the approaching train, f. a testing means controlled by said demodulation means and coupled to said protection control means when an approaching train is detected only by said advance detection means for simulating the passage of a train through said approach warning section and for monitoring the operation of said protection control means to simulate the proper activation of said warning signals in response to the simulated passage of a train, and g. a failure warning means controlled by said testing means for registering a fault condition when an improper operation of said protection control means is detected during a simulated train passage test period,

Claim 8

a receiver means coupled to the rails at the crossing on the opposite side of said highway from the associated transmitter means and responsive only to track current of the distinct frequency of said associated transmitter means for detecting the absence or presence of a train in the corresponding approach warning section as track current is or is not received, d. an energy conversion means also coupled to the rails in multiple with the transmitter means at the distant end of each approach warning track section and responsive only to selected frequency track energy from said energy source for supplying operating energy to the associated transmitter means, e. a train detector means coupled to each energy conversion means and responsive to the reception of energy from said energy source for detecting the absence or presence of a train in a predetermined length of advance track section more distant from the crossing than the associated energy conversion means rail connections, f. a modulating means connected to each transmitter means and controlled by the associated train detector means for applying a first and a second modulation characteristic to the distinct frequency rail current supplied by the associated transmitter means as a train is or is not detected in the corresponding advance track section, g. a demodulating means controlled by each receiver means for registering the modulation characteristic of the rail current received from the associated transmitter means, h. protection control logic apparatus connected for at times activating said warning devices to warn highway traffic of a train approaching within one approach warning section and for deactivating said devices when that train recedes from said highway through the other approach warning section, i. both demodulating means connected to said control logic apparatus for activating said warning devices when one demodulating means first registers the absence of both modulation characteristics, for holding said warning devices active when both demodulating means register the absence of both modulation characteristics, and for subsequently deactivating said warning devices when said one demodulating means registers a first or second modulation characteristic while the other demodulating means registers the absence of both modulation characteristics, j. a testing means coupled to said protection control logic apparatus for at times simulating the passage of a train through said stretch and for monitoring the operation of said protection control logic apparatus to simulate the proper operation of said warning devices in response to said simulated train passage, k. each demodulating means connected to said testing means for actuating a test period when the reception of said first modulation characteristic is registered, for ending a test period when neither modulation characteristic is received, and for retaining said testing means non-actuated when the reception of said second modulation characteristic is registered, and l. a failure warning means controlled by said testing means for registering a fault condition when an improper operation of said protection control logic apparatus is detected during a simulated train passage test period,

Claim 9

a receiver means coupled to the rails at the crossing on the opposite side of said highway from the associated transmitter means and responsive only to track current of the distinct frequency of said associated transmitter means for detecting the absence or presence of a train in the corresponding approach warning section as track current is or is not received, d. an energy conversion means also coupled to the rails in multiple with the transmitter means at the distant end of each approach warning track section and responsive only to selected frequency track energy from said energy source for supplying operating energy to the associated transmitter means, e. a train detector means coupled to each energy conversion means and responsive to the reception of energy from said energy source for detecting the absence or presence of a train in a predetermined length of advance track section more distant from the crossing than the associated energy conversion means rail connections, f. a modulating means connected to each transmitter means and controlled by the associated train detector means for applying a first and a second modulation characteristic to the distinct frequency rail current supplied by the associated transmitter means as a train is or is not detected in the corresponding advance track section, g. a demodulating means controlled by each receiver means for registering the modulation characteristic of the rail current received from the associated transmitter means, h. protection control logic apparatus connected for at times activating said warning devices to warn highway traffic of a train approaching within one approach warning section and for deactivating said devices when that train recedes from said highway through the other approach warning section, i. both demodulating means connected to said control logic apparatus for activating said warning devices when one demodulating means first registers the absence of both modulation characteristics, for holding said warning devices active when both demodulating means register the absence of both modulation characteristics, and for subsequently deactivating said warning devices when said one demodulating means registers a first or second modulation characteristic while the other demodulating means registers the absence of both modulation characteristics, j. a testing means coupled to said protection control logic apparatus for at times simulating the passage of a train through said stretch and for monitoring the operation of said protection control logic apparatus to simulate the proper operation of said warning devices in response to said simulated train passage, k. each demodulating means connected to said testing means for actuating a test period when the reception of said first modulation characteristic is registered, for ending a test period when neither modulation characteristic is received, and for retaining said testing means non-actuated when the reception of said second modulation characteristic is registered, and l. a failure warning means controlled by said testing means for registering a fault condition when an improper operation of said protection control logic apparatus is detected during a simulated train passage test period,

Claim 10

a receiver means connected to the rails at said crossing on the opposite side of the highway from, and responsive only to output signals of, the associated transmitter means, b. an advance detection means for each direction of travel connected for detecting a train approaching the associated approach warning section and also for detecting a train receding from said crosSing beyond that approach section, c. a modulation source separately connected to each transmitter means and controlled by the corresponding advance detection means for modulating the associated transmitter output signals by a first or a second characteristic as a train is or is not detected by the corresponding advance detection means, and d. a separate demodulation means coupled to each receiver means for detecting the reception of the first or second modulation characteristic by that receiver, and in which, e. said protection control means includes control logic apparatus initially responsive to the detection of an approaching train by either track circuit for activating said warning devices, f. said control logic apparatus being further responsive to the detection of the same train by the other track circuit while receding from said crossing in the opposite direction approach warning section for deactivating said warning devices, g. said testing means is controlled by each demodulation means for actuating a test period when the reception of said first modulation characteristic is detected, and h. said control logic apparatus is also controlled by each demodulation means for initially activating said warning signal when neither modulation characteristic is received by a first one of said receiver means, for holding said warning signal active when neither modulation characteristic is received by either receiver means, and for deactivating said warning signal when neither modulation characteristic is received by only the other receiver means.

Claim 11

a receiver means connected to the rails at said crossing on the opposite side of the highway from, and responsive only to output signals of, the associated transmitter means, b. an advance detection means for each direction of travel connected for detecting a train approaching the associated approach warning section and also for detecting a train receding from said crosSing beyond that approach section, c. a modulation source separately connected to each transmitter means and controlled by the corresponding advance detection means for modulating the associated transmitter output signals by a first or a second characteristic as a train is or is not detected by the corresponding advance detection means, and d. a separate demodulation means coupled to each receiver means for detecting the reception of the first or second modulation characteristic by that receiver, and in which, e. said protection control means includes control logic apparatus initially responsive to the detection of an approaching train by either track circuit for activating said warning devices, f. said control logic apparatus being further responsive to the detection of the same train by the other track circuit while receding from said crossing in the opposite direction approach warning section for deactivating said warning devices, g. said testing means is controlled by each demodulation means for actuating a test period when the reception of said first modulation characteristic is detected, and h. said control logic apparatus is also controlled by each demodulation means for initially activating said warning signal when neither modulation characteristic is received by a first one of said receiver means, for holding said warning signal active when neither modulation characteristic is received by either receiver means, and for deactivating said warning signal when neither modulation characteristic is received by only the other receiver means.

Claim 12

said failure warning means also coupled for inhibiting further operation of said protection control logic apparatus in response to the detection of a train by said primary detection means when a fault condition exists.

Claim 13

said failure warning means also coupled for inhibiting further operation of said protection control logic apparatus in response to the detection of a train by said primary detection means when a fault condition exists.

Claim 14

A highway crossing signal system as defined in claim 2 in which each advance detection means comprises an open end track circuit including, a. a power source common with the other advance detection means connected to the rails at the crossing and having a frequency characteristic different from each overlay track circuit, b. the rails of the corresponding approach warning track section and the rails of an advance track section extending a predetermined distance in approach to said corresponding warning section, and c. a normally active detector device coupled to the rails in multiple with the transmitter means of the associated overlay track circuit for receiving operating energy from said power source, d. each detector device responsive to a rail shunt within said predetermined approach distance for registering the occupancy of that advance section by a train, e. each detector device connected to the modulation source for shifting the modulation of the associated transmitter means from the second to the first characteristic when a train is detected in the corresponding advance track section, and f. said power source also coupled at the distant end of each approach warning section for supplying operating energy to the associated overlay track circuit transmitter means.

Claim 15

A highway crossing signal system as defined in claim 3 in which, a. said modulation source provides a first and a second code rate for selectively modulating a particular transmitter means output to supply signal pulses at the selected code rate to said rails as a train is or is not detected occupying the corresponding advance detection section, b. each demodulating means includes a first and a second decoder responsive only to received pulses of said first and second code rates, respectively, for operating to an active condition, c. said control logic apparatus jointly controlled by each pair of decoders for activating said warning signal initially when both decoders of one pair are in the inactive condition, for holding said warning signal activated when all decoders are in the inactive condition, and for deactivating said warning signal when only both decoders of the other pair are subsequently in the inactive condition, said warning signal being normally held inactivated while any one decoder of each pair is in its active condition.

Claim 16

A highway protection system for controlling warning devices for highway traffic where the highway is intersected by a stretch of railroad track over which trains move in either direction, comprising in combination, a. an approach warning track section extending a selected distance each direction from said crossing, b. a source of alternating current energy having a selected frequency coupled to the rails in the vicinity of the highway crossing for supplying track energy to the rails in both directions, c. an overlay track circuit for each approach warning track section, each including,

Claim 17

A highway protection system for controlling warning devices for highway traffic where the highway is intersected by a stretch of railroad track over which trains move in either direction, comprising in combination, a. an approach warning track section extending a selected distance each direction from said crossing, b. a source of alternating current energy having a selected frequency coupled to the rails in the vicinity of the highway crossing for supplying track energy to the rails in both directions, c. an overlay track circuit for each approach warning track section, each including,