Abstract: This invention relates to a system and method of detecting a broken rail in a railway system. The track sensing circuitry of the present invention applies a voltage source at each end of a block of rails and senses the current flowing through the circuitry. The present invention will detect broken rails continuously in a block, even with a train present (except for a break directly beneath the train). Since the rail is continuously checked, the only restriction imposed on train spacing by this track circuit configuration is that only one train can be present in a block at a time.

Abstract: A reliable and consistent electrical contact path between the rails of a section of railroad track established by the shunting effect of the wheels and axles of a train is ensured by applying time-spaced, short duration electrical pulses to the rails at a voltage level sufficient to overcome poor wheel/rail contact. Each of the pulses is produced by a generator that discharges a capacitor across the rails. The narrow pulse width inductively isolates the pulse generator and associated track section from adjacent stretches of track, and the spacing between pulses further avoids interference with other types of electrical track equipment. A detector responsive to the voltage on the rails disables the pulse generator when the received voltage exceeds a threshold and thus indicates that no train wheels are present in the track section. In a grade crossing warning system, once activated the pulse generator and detector assume the role of the island detection circuit and maintain the crossing warning.

Abstract: This invention pertains to model railroads and specifically to the problem of detecting the presence or absence of cars, locomotives, or obstructions which may occupy a particular section of track. Modulated signals of radio frequency are applied to the track via a balanced transformer and detected synchronously. A circuit is provided for nulling the detected signal in the absence of any occupation in such a manner that any change in detected signal represents an item which occupies that track section. The use of radio frequency signals and synchronous detection enables the system to be very sensitive, and to detect objects which do not necessarily form a direct current path across the rails.

Abstract: A track circuit is used in a railway plant or the like, and comprises a track segment which is isolated electrically from the adjacent segments by electrical splices which consist of a conductor connecting the rails in the shape of an "S" laid flat in the direction of the axis of the track. Stationary ground transmission and reception units we provided for each track segment, and on-board mobile reception units we provided on the trains in transit. The data or the information transmitted by the ground units to the on-board units being conveyed through the rails of each isolated track segment when the train is travelling thereon. According to the invention, with each track segment there is associated a compensation network consisting of capacitors connected to the rails of the track segment and suitably spaced apart. Particular embodiments are provided of the electrical splice and of the transmission/reception units.

Abstract: The invention provides for a cab signaling apparatus and method for use on board a railway vehicle propelled on a set of spaced rails by a traction motor. The cab signaling apparatus may reduce a noise component within a signal having a primary cab signal component and reduce a cab signal component within a signal having a primary noise component. The cab signaling apparatus may further include an adaptive filter to cancel the noise component within the signal having a primary cab signal component without specialized tuning of the cab signaling apparatus. The cab signaling apparatus may include a false code monitor for identifying a true cab signal code and a track signal monitor for identifying a true cab signal in the presence of noise.

Abstract: The position of a break in at least one of a pair of rails in an electrically isolated rail segment of a railroad is carried out by measuring current across the ballast between the rails of the segment from one end of the segment when one of the rails in the segment is not broken and subsequently when the rail is broken. A position of the break can be calculated as a function of the ballast current. A linear approximation using the ratio of the ballast current when the rail is broken to the ballast current when the rail is not broken multiplied by the distance of the rail segment from the one end gives a satisfactory approximation of the location of the rail break.

Abstract: This invention relates to railway track circuits. An active track circuit termination unit (4) is connected to the rails and, via a transmitter unit (4a), transmits signals into the rails to terminate track circuits (A,B). The transmitter unit also transmit data signals, for example track circuit signals, into the track circuits.

Abstract: A track code analyzer is disclosed that measures the duty cycle, carrier frequency, modulation frequency, and amplitude of track code signal and determines when these parameters are outside predetermined limits. The system also detects and records transient anomalies in the track code. The track code analyzer of the present invention is either mounted on a railway vehicle or used as a portable, wayside troubleshooting device. In a preferred embodiment, apparatus for processing a track code signal for indicating track conditions is provided that comprises a pickup for inductively receiving and decoding an analog track code signal. The signal is preferably received and processed by a conditioning circuit for processing the analog track code signal and transmitted to an analog-to-digital (A/D) converter for creating a digital track code signal.

Abstract: An improved railway cab signal transmitter for transmitting a cab signal onto a pair of rails for reception by a railway vehicle on said rails. A tuning arrangement is connected across the rails to generally resonate with the leaving end impedance bond at a preselected cab signal frequency. The cab signal is coded at the preselected frequency such that the resonant circuit acts in conjunction with the code signal generation to act as a constant current signal source feeding the rails. A reduction in the maximum cab signal rail current is achieved thereby mitigating runby cab signal currents which might be available for reception by following trains. Embodiments of the tuning arrangement use a capacitor on the primary winding of the feed transformer. Other embodiments include inductance in series with a capacitor. Receivers for wayside displays that also use the cab signal current include embodiments having a capacitor or a capacitor/inductor across the wayside receiver transmitter secondary.

Abstract: A railway track circuit system is described, in which there is a transmitter 15,16 and receiver 19,20 at each end of a track circuit section 4. Each receiver receives signals from the transmitter at the opposite end of the section and the received signals are analyzed to determine whether a vehicle is present in the track circuit section. Where adjacent track circuit sections are also provided with a transmitter and a receiver at each of their ends, the transmitters 14,17 and receivers 18,21 at adjacent ends of adjacent track sections 3,5 can be connected to a track circuit unit 8,9 to allow that unit to check, when a vehicle appears to have left one track circuit section, that it has entered an adjacent section.

Abstract: A receiver for use in receipt of signals on railroad rails which converts the rail signal to a higher frequency and feeds the higher frequency signal into an input transformer. The secondary of the input transformer is in a tuned circuit which is resonate at the higher frequency and which contains a winding of an output transformer. The tuned circuit can be tuned to the higher frequency by series components such as a resistor and capacitor.

Abstract: A railway signalling system for the detection of a train within a defined section of track by means of track circuit apparatus utilizes the rails within the section as part of the track circuit. The rails are electrically shunted by the wheels and axles of a railway vehicle of the train in the section. The presence of a train is detected by detecting the change in the shunt impedance between the rails of the track circuit when a train enters the section. To improve the reliability of the track circuit a shunt assist circuit is provided. This shunt assist circuit comprises an inductive loop aerial provided on the railway vehicle so that it is closely coupled, inductively, with the rails, whereby when the loop aerial is energized from an alternating source, a current is induced in the wheel-rail-axle circuit.

Abstract: A sensing device mounted on a railway locomotive vehicle axle assembly to sense signalling currents conducted through the axle. The device also serves to protect the critical traction motor support bearing from contamination by foreign substances. The sensing device includes a core member mounted in material at least partially covering the bearing and maintaining the core member in position encircling the axle. The core member conducts magnetic flux caused by the flow of current through the axle. An electrical conductor wound about the core member and/or a hall effect sensor embedded within the core member detect the presence of the flux. Clamping bands maintain the mounting material in position about the axle.

Abstract: The invention provides a single-element coded alternating current railway track circuit which may be adapted to a double-element Phase-Selective configuration. A transmitter, via a transmitter transformer, provides a coded track signal to the track. A receiver transformer having one primary winding and a pair of secondary windings receives the track signal. One of the secondary windings is connected directly across a rectifier.The other secondary winding is connected in series with a secondary winding of a local transformer. This serial combination is electrically connected across another rectifier. A DC code-following relay is electrically connected across a rectified output of the first rectifier via two output terminals. A third output terminal allows substitution of a magnetic stick relay for the code-following relay if a double-element configuration is desired. The primary winding of the local transformer has terminals for connecting an AC source when using the optional double-element configuration.

Abstract: A reliable and consistent electrical contact path between the rails of a railroad track established by the shunting effect of the wheels and axles of a train is ensured by applying an alternating current signal to the rails at a voltage level sufficient to overcome poor wheel/rail contact and cause a wetting current to flow between the rails. This likewise provides a current path for railroad control and communication signals, such as the island circuit signal of a grade crossing warning system. The effective range of the wetting current signal is limited by providing the signal with a frequency of 10 KHz or higher to inductively isolate the signal source and associated stretch of track from any shunts beyond that stretch. To avoid interference with other types of electronic track equipment, the signal is applied only when required. In grade crossing warning systems, it is controlled in a fail-safe manner.

Abstract: A railway track circuit for protection of an extended track block having a master unit at one end of the block and a satellite unit at the other. Each master and satellite unit having transmitting and receiving capabilities. The output impedance of the transmitters or of the receivers is of a low impedance as connected to the rails. Through an alternative transmit and receive sequence a link-up between the master and satellite units provides detection of broken rail and/or shunts from each end of the track circuit. The use of low impedance and detection at both ends of the section permit extended length track circuits.

Abstract: A device for protecting track relays from electrical disturbances originating from a train's traction current. The device has: a control signal generator; a signal inverter, to invert periodically the polarity of the signal emitted; and a receiver for the control signal. A distinguishing circuit is provided downstream from the receiver for assessing the frequencies forming the receive signal and switching the track relay to the "line clear" position only after recognition of the frequencies forming the periodically inverted control signal.

Abstract: A multi-frequency shunt is provided for use between the rails of a railroad track to define the approach distance for a railroad crossing using a constant warning time or motion detection device. The shunt includes a housing with a PC board having rail terminals thereon being mounted in the housing. There are connections from the rail terminals of the PC board, extending outwardly through the housing, to the rails. The PC board includes a plurality of inductive and capacitive elements mounted thereon and connected to header terminals which are mounted on a header board. There are straps for interconnecting the header terminals with the interconnections between the header terminals determining which inductive and capacitive elements are connected between the rails and thus determining the nominal frequency of the shunt.

Abstract: The invention is a conveyor control system having self-propelled vehicles having wheels, each driven by a motor (14) to move along rails. The system includes power rails (18) for supplying power to the vehicle (12) and at least one command rail (20, 21) which transmits a constant command signal indicative of requested speed. The command rail (20) is comprised of isolated sections of rail for carrying different command signals along each isolated section to enable the vehicle (12) to travel at different speeds dependent on which section of rail the vehicle is within. The command signal may be in the form of an analog signal on one rail (20) or a digital signal on two rails (20, 21). Each vehicle (12) includes a control circuit (22) which interprets the command signal to drive the vehicle (12) at the requested speed. An override circuit (28, FIG. 2b, FIGS. 3 and 4) senses external activity for proper control of the circuit.

Abstract: A railroad track fault detector is mounted on a tracked vehicle and uses the track ahead or behind the vehicle as a transmission line for a high frequency signal. The transmission line has a known characteristic impedance in a condition of no track fault. The impedance is included in a bridge network that is excited with the high frequency signal. Bridge imbalance is detected as an indication of a track fault that can be a complete or partial short circuit or open circuit. The bridge excitation is applied to the track through moving contacts like brushes ahead of the front wheels or behind the last wheels. The shunt effect of wheels close to the brushes is eliminated by a tuning impedance that creates an effective infinite impedance to the portion of the track between the moving contacts and the shunting wheels.

Abstract: A communication system for a railway train has a proving circuit for proving conditions of the railway track ahead of the train. The proving circuit comprises a transponder associated with at least one rail of the track to form a rail circuit therewith. The response of the transponder to an interrogater on the train is dependent upon the condition of the rail circuit.

Abstract: The apparatus of this invention is a broken rail detection system that detects rail and/or rail breaks in dark territory track sections, i.e. track sections that do not have signalling systems. In one embodiment of this invention a system is disclosed in which a communications link exists between the ends of the track sections and in another embodiment of this invention no communications link exists between the ends of the track sections.

Abstract: An automatic vehicle protection system, e.g. for a railway vehicle, in which continuous contact is maintained with a train via transmissions carried by the normal track circuit signals. Information relayed to the train through these transmissions may concern speed limits, forward section occupancy and so on which can replace normal track side visual signalling systems as a means of controlling trains. It is, therefore of utmost importance to ensure that a train receives the correct transmission, which it is intended to receive, and not those meant for other trains. By arranging for track circuit signal freqencies in predetermined sequences and providing the train with means for determining whether or not the sequence of frequencies it encounters as it traverses a line the safety of the train, and the integrity of the system may be continuously proved.

Abstract: In railway signaling systems which transmit rate code signals along track circuits, which signals are picked up by the trains and used for signaling purposes, such as speed control, the rate code signals of the same repetition rate received when the train passes between adjacent track section may suffer a phase shift, also known as a phase jump. To prevent loss of the rate code signal during a phase jump, an improved rate code decoding system is provided wherein a correlation process is applied to the received rate code signal by multiplying the signal in separate multipliers with reference signals which are in quadrature and then cross-correlating the output of the multipliers with a step function and summing the absolute values of the outputs of the cross-correlators to provide a level which is substantially constant in the presence of a phase jump.

Abstract: Broken rail detection in a block of track without the need or expense of conventional signalling uses a chain of transmitters and receivers connected to the rails and defining sections of the block between the ends of the block. Either cyclically at a predetermined code rate or upon command of an external unit; an alternating current (AC) signal is launched from one end of the block and is repeated at different frequencies in each of the sections. When received at the end of the block, an indication of the absence of a broken rail condition is given either (a) by way of pole line or radio communication to a central control or dispatcher point and thence back to the trains, or (b) signals at the ends of the block are flashed at the code rate. The detected signal at the code rate may be used to modulate a direct current which is transmitted along the rails in the block to a signal at the opposite end of the block which also flashes at the code rate to indicate a safe condition.

Abstract: An improved audio frequency track circuit system utilizes a synchronous train detection arrangement and reduces the number of fixed code rate modulated carrier signals. As few as two carrier signals are alternately applied at discrete points along a pair of jointless track rails to define the transmitter ends of the track sections, with complementary receivers defining the opposite ends. The two carrier signals are coded at one of two phase angles which are 90.degree. out-of-phase so that, when assigned, the nearest possible interfering signal is 90.degree. out-of-phase and is rejected thereby. Like carrier frequency transmitter/receiver arrangements are disposed on opposite sides of an insulated joint but are coded 180.degree. out-of-phase so that a breakdown of the insulated joint is detected and the false code signal is rejected.

Abstract: An alternating current code, alternately transmitted in each direction through the rails of a railroad track section, includes a selected number of pulses of alternately positive and negative polarity similar to a bi-polar DC code. Data is transmitted by pulse length, with long and short pulses representing binary digits 1 and 0, respectively. The code pattern, polarity and pulse length, is balanced to eliminate code distortion by track energy storage. The code pattern transmitted is determined, and received pulses are decoded, by a microprocessor with associated memory (PROM) which processes local input and output data. The processor also checks the operation of the associated apparatus, including input and output circuit and hardware integrity through monitor devices and feedback signals. A unique check signal output is produced only when the various monitor networks determine all operation is proper and that the various elements are free of faults.

Abstract: A device for detecting the unbalance .DELTA.i between the two fractions of the return traction current flowing in the two rails of a railroad track, in the presence of a signalling current in the respective track circuit, includes a linear combination circuit (3) that receives two signals (i.sub.1 and i.sub.2) which are proportional to the two currents actually present in the two rails and obtains both the difference (i.sub.1 -i.sub.2) and the sum (i.sub.1 +i.sub.2) thereof. A demodulating circuit (4), fed with the difference signal, takes from it the modulating signal of the signalling current and feeds it to a sample generator circuit (5), which generates a sample function M(t). The sample function is supplied to two successive sampling circuits (106 and 206), one of which also receives the difference signal and produces a sampled difference signal M(i.sub.1 -i.sub.2), while the other also receives the sum signal and produces a sampled sum signal M(i.sub.1 +i.sub.2).

Abstract: A vital, or fail-safe, track circuit wheel detector for detecting the presence and position in a given detection zone of wheel-axles on railroad cars; in order to provide the requisite fail-safe indication, the operation of the system relies on a sensing means which produces two distinct output signals. The sensing means includes a biasing arrangement for providing, even in the absence of wheel-axles, a steady output signal derived from the path of normal feed current flow. This bias signal is countered or opposed by a wheel sensing signal from the same sensing means responsive to flux level changes resulting from the presence of particular directional components of wheel-axle shunt current, whereby a dip or net reduced signal is effectuated; in the case of open circuit conditions, the output indication goes to zero when there are no wheel-axles in the detection zone.

Abstract: This vital solid state relay incorporates only passive elements and is intended for use as a replacement for a two element AC track relay in AC track circuits. The local input signal is applied to a transformer whose secondary output, across a Zener diode, is a pulsed, square wave DC with regulated peak. The track input is applied through a noise rejection filter, tuned to track circuit frequency, to a coupling transformer. A series loop registry circuit includes the secondary of each transformer, a DC relay, and a varistor element. The sum of the transformer output signals, due to the Zener diode rectification, has a DC component. When local and track signals are both present and substantially in phase, the varistor switches to its high current condition to pick up the DC relay to indicate an unoccupied track section. Absence of the track input, out of phase conditions, or unmatched frequencies retains the varistor in its low current state and the DC relay releases to register an occupied section.

Abstract: A railway signalling receiver in which a signal carried by the railway lines is sensed and the sensed signal is sampled, digitized and subjected to a discrete Fourier transform operation which transform the time domain samples into the frequency domain. The frequency content of the signal may then be examined in order to identify the original signal or to decode the information carried. The signal may be a frequency shift keyed carrier signal. A technique of maintaining the safety of the system by discriminating against potentially confusingly similar ASK signals, which can arise spontaneously in electric traction territories, is described. A technique of digitally heterodyning down a carrier signal so that the transform operates on the lower sidebands frequencies in order to maximize efficiency of the transform calculations is also described. The receiver is useful as a jointless track circuit receiver and also in a part of the train borne equipment of an automatic train protection system.

Abstract: A railroad train detector and communication system relies on the track rails for communicating information among a plurality of locations. The equipment located at each of the locations eliminates relay based current detection, relay based current transmission, and relay based logic functions, and rather these functions are implemented with microprocessors. An extent of signal trackway is defined between a pair of head ends, intermediate the head ends at intermediate insulated joint locations, a microprocessor implemented transmitter/receiver pair is provided. One half of the transmitter/receiver pair manages communication flow for each direction of information flow at the joint. At each of the head locations, only a single transmitter/receiver is required. Associated with each microprocessor in a transmitter/receiver is auxiliary apparatus to couple the microprocessor's input/output ports to the track rails themselves.

Abstract: A voltage variation detector is connected to a receiver which is associated with a transmitter inducing an alternating signal permanently in the rails of a railroad track and, accordingly, in a conductive loop positioned between the rails. The respective variations of the voltage induced in the loop and of a feeding voltage to the loop furnish redundant information of the presence of a car in the transmission zone.

Abstract: A receiver for sensing track currents includes a toroid coupled to the track rails via a single conductor. The toroid has an air gap in which a linear Hall sensor is inserted. The voltage of the Hall sensor is applied to signal processing circuitry including a low pass filter, amplifier and level detectors. In one embodiment of the invention comprising a track occupancy detector, second and third windings coupled to the toroid are selectively energized from a potential source to provide MMF's in the toroid of one and another polarity, and of a level less than the MMF provided by an occupied track section. The amplifier includes first and second channels for amplifying signals of opposite polarities. Each channel of the amplifier is coupled to a pair of level detectors, one of the level detectors in each pair is a vital level detector with the threshold set at about 50% of the threshold of the other level detector in the pair.

Abstract: An improvement in apparatus for the secure transmission of information through rails in zones of propagation independent from the sections of the track block-section system embodying the use of series resonant circuits tuned to the information carrier frequency and connected between the rails at the end of a transmission zone and comprising two identical series resonant circuits disposed in parallel and each comprising a capacitor in series with the primary winding of a transformer, with the secondary windings of the two transformers being connected in series and in opposition, so that an oscillating signal appears at the terminals of the circuit thus formed in the case of failure of one of the resonant circuits.

Abstract: The two inputs of a first flip-flop (FF) are alternately energized over a pair of opposite contacts of a code transmitter. Outputs of a second FF alternately enable a pair of logic gates to pass first or second output pulses of the first FF as clock pulses which drive a counter which produces an output pulse after each preselected count X. Each counter output pulse, equal in length to a half cycle of the code, triggers the second FF to its opposite state. A magnetic stick code repeater relay is driven between its two positions by energy supplied from a normally active driver circuit over another pair of opposite contacts of the code transmitter. The driver circuit is optically coupled to be turned off during each counter output pulse, thus inhibiting repeater relay operation during the corresponding half code cycle. This relay holds in its existing position, blanking a half cycle code period, and then is held by the again active driver circuit during the subsequent half cycle.

Abstract: A railroad signal circuit includes a transmitter and a receiver which have a common connection to the track rails at one end of a signal block. There will be a similar transmitter and receiver at the opposite end of the signal block. A transmit/receive switch is connected in circuit with the transmitter and there is a code following element connecting the receiver to the transmit/receive switch and transmitter. The code following element comprises a Hall effect cell whose output is connected to the receiver.

Abstract: Coded energy applied to the track circuit rails for cab signal control when a train occupies the section is also applied over a line circuit to the local input of the solid state track relay unit and to a code reset module in which it drives a code following relay and charges a timing capacitor during a predetermined number of code pulses. When the section becomes unoccupied, the track relay unit produces a coded output, from the combined rail and local inputs, to which the track registry relay is non-responsive. An analog storage circuit in the reset module receives and stores this coded output energy during each timing period. During each code off-time, the timing capacitor is connected to a switching relay circuit controlled by a DIAC unit.

Abstract: A tuned transformer element has its primary winding coupled, in series with a fuse of preselected rating, to the rails of the track circuit. A secondary winding supplies input energy to the track circuit receiver unit which detects occupancy conditions of the track section. A third winding is capacitor tuned to resonate with the primary winding at the track circuit frequency. Thus the transformer appears as a parallel resonant load of high impedance in multiple with the track receiver which then operates normally. At propulsion frequency, the impedance of the primary is small while the parallel capacitive reactance is large, so that the parallel network gives the transformer unit a low impedance at this frequency.

Abstract: A railroad signal system includes an A type transmitter and receiver for sending and receiving signal messages in one direction and a B type transmitter and receiver for sending and receiving signal messages in the opposite direction. The A transmitter and the B receiver are located at one end of a signal block and the B transmitter and A receiver are located at the opposite end. The A transmitter provides an A type DC message and the B transmitter provides a B type DC message. The A receiver is responsive to only an A type message and the B receiver is responsive to only a B type message.

Abstract: A vehicle train tracking apparatus and method are provided for responding to detected occupancies and unoccupancies of each of a plurality of signal blocks of a roadway track system to establish a position or location record of the movement of each vehicle train operating with the roadway track system.

Abstract: An audio frequency track circuit with improved security in the train detection function for rapid transit applications for use with uninsulated rails includes an improved transmitter and receiver. The transmitter modulates a track frequency carrier with a fixed code rate, regardless of the code rate employed to modulate the train information frequency. The receiver includes a decoder tuned to the track frequency modulation rate. By using such a sharply tuned decoder, the noise protection threshold is increased. Because of its application to uninsulated rails, with the associated lack of hard track circuit boundaries, adjacent track circuits have different track frequency modulation rates to insure that the modulated track frequency signal, from one track circuit, is not effective to operate a track relay in another circuit even under failure conditions.

Abstract: A process for coding track circuits allows particularly information to be transmitted to a vehicle travelling over a railway track divided into a succession of sections each equipped with a track circuit, in which each of the carrier frequencies for energizing the track circuits is frequency modulated by means of a number of modulation frequencies each representing a piece of information to be transmitted. This process includes the steps of comparing the modulation frequency obtained by demodulation of the modulated carrier frequency with another source of modulation so as to check that said modulation frequency is indeed correct, and to allow transmission of the modulated carrier frequency in the corresponding track circuit only when this check is positive. This process and device applies to high-speed railway trains.

Abstract: Disclosed is an aerial transport system which comprises an aerial track having therealong a pair of electric current-carrying cables in a parallel relationship with respect to one another and with respect to the track, and self-propelled carriages. Each carriage has an electric current collector to collect electric power from the current-carrying cables and to supply the power to an electrical driving mechanism mounted thereon for driving wheels engaging with the track. The current-carrying cables are separated at longitudinal given intervals so as to define respectively independent electric power supply zones. The transport system further includes a system for controlling electric power supply for the vehicle or carriage including a mechanism for detecting a vehicle or carriage position in the track provided in each power supply zone.

Abstract: A railroad track monitoring device has a response device disposed at the front and end of every train, the response devices being capable of transmitting one of a number of different signals to a sampling device. The number of signals is at least twice as large as the number of trains on the system. The track is subdivided into a number of successive path segments and an interrogation device is disposed at the boundary of every two adjacent path segments. Each interrogation device has a memory allocated thereto for storing the last-received signal from a train passing the interrogation device, and a series of comparators for comparing the signals received from interrogation devices associated with adjacent track segments releases an occupied signal or a open track signal upon coincidence or difference of the most recently received information from the two track sections behind the front of the train.

Abstract: A railroad highway crossing warning system including pickup coils for sensing current flowing in the track rails of an approach zone, a circuit for sensing the voltage across the track rails, band-pass filter circuits for filtering the voltage and current derived from the track rails, impedance calculator circuits for calculating the track impedance, phase detector circuits for detecting the phase angle between the voltage and current, a multiplier circuit for linearizing the track impedance by multiplying the track impedance by a function of the phase angle, a data sampler circuit for sampling the linearized track impedance at given periodic intervals, a motion detector and crossing predictor circuit for detecting the motion of a train and for predicting the time of arrival at the crossing by comparing the predicted time of arrival with an advanced warning time, and a logic gate circuit for activating the warning apparatus at the crossing when the predicted time of arrival is less than the advanced warning t

Abstract: A selected unique digital comma-free code word is transmitted through track section rails from one end and, when received at the other end, is applied serially to a shift register which supplies a parallel readout of shifting pattern to one input of a fail-safe comparator. The second comparator input is selected from the different possible digital code patterns of the track code word stored in a memory device. When inputs are equivalent, the comparator passes an input test signal to its output. Absence of comparator output causes the selected stored code word to be stepped through the stored patterns, in reverse order to track code shift, until equivalence is again obtained. The periodic output signals, of approximately 50% duty cycle, are processed through a series filter-rectifier network, tuned to test and periodic output signal frequencies, to energize a track relay to register an unoccupied track section indication.

Abstract: An electronic system which emulates the operation of a polar relay for applying coded pulses to railway tracks has separate signaling circuits having signaling devices responsive to a separate inputs which provide operating power to the circuits. The circuits are interlocked by connecting the inputs to the signaling devices in inverse relationship. One input excludes the other. The signaling devices may be light emitting isolators with switching transistors which control the application of current pulses through the rails of the track while isolating the track battery which supplies the current for these pulses from the local battery which provides the inputs to the signaling circuits. The signaling circuits establish current paths through the light emitting signaling devices at predetermined times after the inputs are applied to emulate the pickup and drop away time of the polar relay.

Abstract: A highway crossing warning system for monitoring the motion and predicting the time of arrival of an approaching train at the highway crossing and for detecting the presence of a broken rail in the approach zone by feeding dual frequency signals into the track rails and measuring the track impedances at the two frequencies and the phase angle of the lower of the two frequencies.

Abstract: A cross field transformer circuit arrangement for use as a solid-state, synchronous detector track relay device for alternating current track circuits. The track signal at the receiver end is applied to the primary winding on the main magnetic circuit and the local input signal to another primary winding on the modulating magnetic circuit of the saturable core of the transformer. Each input is transformer isolated from its source and passed through a noise-rejecting filter tuned to track circuit frequency. The main magnetic circuit flux is modulated by the modulating magnetic circuit cross field flux so that the secondary winding, on the main magnetic circuit, produces an output signal at double the track frequency, i.e., its second harmonic. A band pass output filter passes only this second harmonic signal to a full-wave rectifier to energize a biased track relay only when both inputs, in phase and of the same frequency, are received.