Abstract: An inductive sensor is driven by a series resonant oscillator circuit to produce an oscillator signal having a frequency which is a function of inductance of the inductive sensor. An inductive load, which includes the sensor, is connected in series with a capacitive impedance. Power to the series resonant circuit formed by the inductive load and the capacitive impedance is controlled as a function of current in the series circuit as sensed by a current sensor. A detection system provides a detector output based upon the frequency of the oscillator signal.

Abstract: This arrangement enables the identification of a plurality of vehicles (4) and determination of the instant of their passing over a reference line (30). It includes a moving station (1) mounted on the vehicle and a fixed station (2) arranged alongside a racetrack (3). The fixed station broadcasts a low-frequency synchronization signal of period T which is received by the moving station, the latter in turn broadcasting a series of signals of duration Tn located in a predetermined rank relative to the time t.sub.o marking each start of period T. Conjointly the moving station allocates an identification code peculiar to a given moving object to each signal Tn. The signals received by the fixed station are stored in a memory which for each signal memorizes its absolute time, its association with a given vehicle and its amplitude. The arrangement is used for motor vehicle races which include a large number of competitors.

Abstract: Apparatus for detecting an automatic guided vehicle's longitudinal position and to enable positioning of the vehicle at a load pickup/delivery terminal or other place. In one arrangement a mat having a passive short-circuited loop of wire embedded in it is positioned on the floor. On the vehicle an oscillator and a transmitting antenna provide a primary magnetic field that excites the loop in the mat, inducing current in the loop. The loop current produces a secondary magnetic field. Magnetic receiving antennas on the vehicle detect the secondary magnetic field that is caused by portions of the loop that cross the longitudinal axis of the vehicle. Onboard electronic apparatus ascertains and can control the longitudinal position of the vehicle relative to the mat. The same on-board apparatus enables the vehicle to detect a directly energized (connected to a power source) guidewire in the floor that lies across the vehicle's path between terminals and at terminals.

Abstract: A method and system for transferring information between a moving vehicle and a stationary information location having a vehicle detector system with a loop antenna by using the loop antenna as either the receiving antenna for signals transmitted from a moving vehicle or as the transmitting antenna for signals generated by a transmitter located at the vehicle detector site for transfer to a receiver mounted on a moving vehicle. The information is encoded on a carrier having a frequency outside the normal frequency range of the vehicle detector system, preferably by interrupted carrier pattern processing.

Abstract: The present invention provides a simulator which when used aboard a vehicle normally undetectable by a traffic signal control system (e.g. A.C. energized buried sensing loop type which detects predetermined changes in the characteristics of an electromagnetic field due to the presence of a detectable vehicle therewithin), will substantially simulate the characteristics of a detectable vehicle within its field and thereby cause any activation of the system. Operationally, the simulator derives an electrical signal from the field (e.g. via a receiving antenna), converts the electrical signal into a modified transmittable signal of an amplitude which when impressed upon the field (e.g. via a transmitting antenna) simulates electromagnetic influence of a detectable vehicle therewithin which is sensed by the detector circuitry and activates an associated traffic signal controller to provide the necessary signals (e.g. a green arrow) to allow safe and unobstructed traffic flow at an intersection.

Abstract: A method of updating the reference count in a period shift measurement vehicle detector permits conditional reference count updating in the No Call direction whenever the sample count minus reference count difference value lies between the upper limit of a jitter/vibration guard and band and a positive freeze reference threshold. Decrementing of the reference count is permitted in the call direction whenever the sample count minus reference count lies in a range from 0 to a negative freeze reference threshold. Variable hysteresis for call/no call signal generation is provided in a single vehicle detector, with the call direction threshold selectable between two values.

Abstract: A ground guidance system for airplanes in which loop coils of a predetermined shape are continuously buried in a specific section of a taxiway for airplanes, an airplane is continuously detected based on changes of self-inductances of the loop coils with movement of the airplane while discriminating airplanes from other objects and admission or inhibition of advance in the specific section to a subsequent airplane according to the presence or absence of the airplane in the specific section and which has a fail-safe structure not generating an output at the time of a system or circuit failure or accident.

Abstract: Timing and warning system for use on a track involving a plurality of vehicles (12,13,14) including a series of stationary transceivers (15) located at selected locations along the track (11) and a mobile transmitter (18) located in each vehicle.

Abstract: A method and system for transferring information between a moving vehicle and a stationary information location having a vehicle detector system with a loop antenna by using the loop antenna as either the receiving antenna for signals transmitted from a moving vehicle or as the transmitting antenna for signals generated by a transmitter located at the vehicle detector site for transfer to a receiver mounted on a moving vehicle. The information is encoded on a carrier having a frequency outside the normal frequency range of the vehicle detector system, preferably by interrupted carrier pattern processing.

Abstract: A vehicle detecting system for detecting the number of vehicles which pass the roadway, thereby realizing the smooth flow of vehicles. This system comprises: a transmitting coil and a receiving coil which are arranged on both sides of the vehicle detection area set over the roadway; a driving circuit to supply a high frequency exciting current to the transmitting coil; and vehicle detecting circuit to output a vehicle detection signal in response to a change in level or phase of the electrical signal which is induced in the receiving coil. The detection signal is outputted when the signal level exceeds a predetermined value or when the signal phase exceeds a predetermined angle. One or a plurality of pairs of transmitting and receiving coils may be buried under the roadway surface or on above the roadway at regular intervals. With this system, the installing construction of the coils is simplified and the possibility of the occurrence of the accident such as disconnection of the coil is reduced.

Abstract: A strip material (18) for forming an inductive loop (10) adapted to be applied to the surface of a roadway (12). The strip material (18) consists of and the loop (10) is formed from a ductile, flexible, flattened, extensible conductor (20) and a protective covering (22). A protective underlayment (24) is optional. The conductor (20) may be formed from a compressed, flattened metallic wire braid (28) or from a wire mesh containing 25% to 75% voids. The protective covering (22) may be formed from either combination unvulcanized elastomer precursor base sheet (30) and a vinyl based polymer support film (32), or a covering (26) selected from the group of epoxy, polyester, urethane and polyurethane.

Abstract: An induction loop and a method of making an induction loop having conduit sections connected by a coupling assembly. The coupling assembly includes a passageway-defining body having ends for receiving sections of conduit. An intermediate body portion includes an opening exposing an intermediate passageway exteriorly. A lid for sealingly covering the opening includes an extension placeable into the opening for mating engagement with corresponding wall portions of the coupling body. The body and lid provide lateral external-pressure-withstanding structure to prevent damage to the assembled loop by absorbing regional pressures. This structure also provides for internal-pressure-withstanding sealing between the two so that, after completion of insertion of conductor in the conduit loop, the conduit may be injected under increased pressure with a heated rubberized asphalt sealant which is flexible at ambient conditions.

Abstract: An induction loop vehicle detection system and method of making and installing such a system are disclosed wherein the conduit sections containing the induction loop are preformed and prewired integrally with all interconnects by using removable expansion joints to assemble sections of prewired and sealed conduit in any desired configuration. The expansion joints can be removed after assembly to enable the induction loop to be folded down for shipment. The expansion joints also enable longitudinal displacement of the induction loop conduit due to thermal differential expansion during installation and during extreme changes in temperature over the lifetime of the system, thereby preserving the integrity of the roadway and fault free operation of the induction loop. The wires forming the induction loop are completely sealed within the conduit with an asphalt rubber material thereby precluding any moisture penetration.

Abstract: A method and system for transferring information between a moving vehicle and a stationary information location having a vehicle detector system with a loop antenna by using the loop antenna as either the receiving antenna for signals transmitted from a moving vehicle or as the transmitting antenna for signals generated by a transmitter located at the vehicle detector site for transfer to a receiver mounted on a moving vehicle. The information is encoded on a carrier having a frequency outside the normal frequency range of the vehicle detector system, preferably by interrupted carrier pattern processing.

Abstract: A vehicle detecting system detects the existence of a vehicle on a roadway and communicates therewith in the following manner. A pair of transmitting and receiving coils are arranged on both sides of a detection area set over the roadway of the vehicle. The first high frequency signal of the first frequency is applied to the transmitting coil to form the high frequency magnetic field between those coils. The existence of the vehicle is detected on the basis of the point such that the characteristic such as level or phase of the signal induced in the receiving coil changes due to the vehicle which entered the magnetic field. The first high frequency signal which is applied to the transmitting coil is modulated by the data to be transmitted to the vehicle. Or, the second high frequency signal which has the second frequency different form the first frequency of the first signal and is transmitted from the vehicle is received by the receiving coil and demodulated.

Abstract: An interrogator-responder communication system in which responders are carried by vehicles (such as railroad vehicles) travelling along a route and in which an interrogating station situated along the route operates each passing responder to recall data from a memory in the passing responder. In one embodiment, the responder is equipped to receive data transmitted from a transmit station and to store the received data, for later recall, in a non-volatile, electrically erasable read/write memory.

Abstract: An inductive loop presence detector, more especially a vehicle detector, including a loop oscillator having an inductive loop connected as a frequency determining element of the oscillator, which inductive loop may be buried in a roadway to sense the presence of vehicles, and sensing circuitry to detect changes in the loop oscillator frequency due to vehicle movements in the vicinity of the loop, with a filter network inserted between the output of the loop oscillator and the sensing circuitry to improve performance when cross-talk occurs due to mutual interference between a number of inductive loop detectors forming part of a total installation. The filter network can be a phase-locked loop incorporating a low pass filter to attenuate high frequency components due to cross-talk.

Abstract: In a vehicle presence detection system in which an inductive sensor loop is the frequency-determining element of the tuned circuit of a loop oscillator, discrimination against variations in inductance due to environmental changes is achieved by comparing detect and tracking reference numbers with a sample number that is a function of the oscillator frequency and updating each reference number repeatedly at real time intervals independent of loop oscillator frequency. The current sample number is compared with either the tracking reference or the detect reference according to whether or not the system is indicating the presence of a vehicle.

Abstract: Timing system for use on a track involving a plurality of vehicles including a series of stationary transceivers located at selected locations along the track and a mobile transmitter located in each vehicle.

Abstract: An electrical proximity identification system which has lateral flux. The system has a reader section with a reader antenna which is comprised of a pair of coils. The coils are located in the same plane and are oriented such that when they are energized by radio frequency power, the flux lines travel between the coils in a direction parallel to, but above and below, said plane. The system also has an identifier section with an identifier antenna. The identifier antenna is positioned such that its axis is parallel to the plane and in line with the flux lines.

Abstract: A method and system for transferring information between a moving vehicle and a stationary information location having a vehicle detector system with a loop antenna by using the loop antenna as either the receiving antenna for signals transmitted from a moving vehicle or as the transmitting antenna for signals generated by a transmitter located at the vehicle detector site for transfer to a receiver mounted on a moving vehicle. The information is encoded on a carrier having a frequency outside the normal frequency range of the vehicle detector system, preferably by interrupted carrier pattern processing.

Abstract: A railway detection system in which the presence of a train is detected by means of first inductive loop apparatus. When the train is detected second inductive loop apparatus is enabled to detect the passage of wheels of the train.

Abstract: A microprocessor controlled loop detection system to be connected to a number of inductive loops which are buried in a road bed and which is used to detect the presence of motor vehicles above the loops to control the operation of traffic lights at an intersection. A common oscillator is connected to each loop on a time-shared basis under the control of a microprocessor, and the frequency of the oscillator in each instance is dependent upon whether or not there is a vehicle above the loop. The microprocessor provides a null time as the system is switched from one loop to another to prevent spurious responses in the system due to transient signals. The microprocessor acts to count the number of cycles of the output signal of the oscillator which occur during a predetermined time interval as each loop is connected to the oscillator by the microprocessor to determine the oscillator frequency for each loop and thereby detect the presence of a vehicle in the particular loop.

Abstract: In a vehicle detection apparatus having a plurality of channels, each arranged for detecting vehicles according to their influence upon the frequency of a respective loop oscillator the oscillation frequency of which is dependent on the inductance of a respective vehicle-sensing inductive loop, a common computer performs a calculation for each channel in turn whereby changes in the frequency of the respective loop oscillator are monitored and analysed. In one embodiment, the computer calculates an appropriate operational number, the time taken for that particular number of loop cycles to occur is measured and stored as a period count and the period count is compared with an environmental reference number to determine whether or not a vehicle detected flag should be raised or lowered. Neither the operational number calculated by the computer nor the reference number is fixed but provision is made for updating both.

Abstract: An inductive loop detector which includes a detector which is coupled to the loop by means of a parallel tuned circuit and a receiver which is coupled to the loop by means of a parallel tuned circuit, with the two tuned circuits having different resonant frequencies.

Abstract: An inductive loop has its frequency of oscillation controlled by means of a counter, a reference frequency source, a comparator, and an attenuator. The frequency of the loop is compared by the comparator to the frequency of the reference source to produce an error signal which controls the attenuator. The amplitude of the output signal of the attenuator is used to adjust the loop frequency to a desired value.

Abstract: An automatic information transmission system for a mobile object, the system including a response unit arranged to be carried along with the mobile object, and an interrogation unit arranged to be disposed alongside the path of movement of the mobile object for movement of the response unit past the interrogation unit. The interrogation unit is arranged to emit a carrier signal at a first frequency and to receive a signal at a second frequency different from the first frequency.

Abstract: An eddy-current loop detector operates to sense the presence of an electrically conductive object by applying D.C. onto a conducting loop so that a permanent magnetic field is induced, which field partly penetrates into the object; ensuring the quick cessation of self-inductive transient operation of the loop when the D.C. is switched off; and measuring the change in the part of the flux passing through the measuring loop arising from eddy-currents induced in the conductive object, and evaluating such change while the relatively slowly decreasing flux is maintained. By repeating these operations with the desired frequency, the eddy-current detector is well suited for continuous measuring of the position of the object.

Abstract: A railroad train moving along an approach to a grade crossing (or other location of interest) is detected by apparatus that is responsive to the change in effective track impedance caused by the moving shunt. A constant current AC signal is applied to the track adjacent the crossing, and the resulting voltage changed in amplitude and phase is picked off by a receiver on the opposite side of the crossing. Voltage and current information derived from these signals is inputted to a microcomputer which calculates the track impedance and determines whether or not a warning device or devices at the crossing should be activated. Such determination is made on a repetitive basis in accordance with a repeating program loop and stored in memory.

Abstract: An induction loop vehicle detector comprises an oscillator circuit having a plurality of capacitors switchable in circuit with a road loop under the control of a microcomputer to determine the oscillator frequency. The microcomputer monitors the oscillator frequency and controls the switching of the capacitors to periodically return the frequency to a predetermined value. A counter counts a predetermined number of oscillator cycles and gates of h.f. clock into a second counter whereby the count of the counter represents the oscillator period. A "vehicle detected" output is given when the monitored frequency alters by more than a predetermined amount, representing a decrease in the inductance of the loop. On detecting an increase in the inductance above a predetermined threshold the detector is inhibited for a predetermined time, e.g. about 1 second, to avoid errors caused by magnetic effects.

Abstract: Apparatus and method for a circuit which is connected in series between the call signal output of a vehicle detector and the call signal input of a traffic controller is disclosed. Under normal operating conditions the invention acts as a signal buffer and input of the invention will be applied to the input of the traffic controller when call signal inputs are continuously present or not present for preestablished times, then test procedures are implemented. During a test or failure condition of the vehicle detector, the detector output signal will be disconnected from the controller. The invention also provides a circuit which is connected between the loop and the loop input of the vehicle detector. The circuit along with the accompanying method is designed to modify the input impedance to the vehicle detector to apply a test or "forced" call signal to the vehicle detector input when a call signal input is not received after a predetermined period of time, a fault condition is established.

Abstract: Location-representative signals are communicated to vehicles (12, 14, 16) by modifying existing traffic detector stations of the type utilizing an inductive coil (20) embedded in the roadway (22). Circuitry (44-52) is provided for generating a carrier signal modulated in accordance with a modulating signal representative of the location of an associated traffic detector station. A transformer (56) couples the modulated carrier signal into the existing inductive coil such that the coil establishes a magnetic field above the roadway which is modulated by the location representative signals. The vehicles have inductive coils (70) mounted thereon for sensing the modulated magnetic fields, and circuitry (72, 74, 76) for extracting the location-representative signals therefrom. The location-representative signals may then be, e.g., automatically transmitted to a central dispatching station (18).

Abstract: A warning device, for a helicopter with a tail rotor and a mechanical protection device (15) therefor, for giving warning if the helicopter tail approaches too closely the ground or an obstruction. The warning device comprises a height-finder (11) with a transmitting/receiving antenna (26) mounted at the helicopter tail to produce a height-finding beam backwards and obliquely downwards. Height signals are processed by computing means (12) to determine the sink rate of the tail and in dependence upon this sink rate and the instantaneous height, a warning signal is initiated if this corresponds to a predetermined relative relationship. The higher the sink rate the greater is the height at which the warning signal is initiated and vice versa.In the preferred arrangement the beam is directed substantially along or parallel to the axis of the mechanical protection device (15).

Abstract: A Hall effect element, incorporated into an integrated circuit unit with temperature compensation, voltage regulation, and amplification, is mounted on top of a permanent magnet made of ceramic material with the critical Hall axis aligned with the magnet pole axis. To avoid saturating the Hall cell, it is positioned within a pole-to-pole hole in the magnet, which creates a flux null space. The permanent magnet and Hall cell assembly is mounted on the rail a predetermined distance below the top so that the flange of passing wheels occupies the air gap between the magnet and the rail through which the major portion of the magnet flux flows. Reduction of the air gap increases the level of the magnet flux and thus the level of voltage output of the Hall cell. The output of the Hall cell is applied to a Schmitt trigger whose switching level is set by a threshold voltage unit.

Abstract: A personnel monitoring and locating system is disclosed that is particularly well suited for monitoring and/or locating underground miners. A plurality of remote terminals having transceivers associated therewith are positioned in a mine and periodically are caused to transmit interrogation signals. Each miner to be monitored is equipped with a transponder that replies to the interrogation signal with the reply signal being timewise delayed by a predetermined amount of time that is different for each of the transponders in use so that the reply from each transponder is timewise spaced from every other interrogated transponder. A host computer at the surface is linked to each remote terminal for transmission of information with information from the remote terminal being indicative of the location of each transponder equipped miner.

Abstract: A vehicle detector has an inductive sensing loop that is a frequency determining element of an oscillator. A first counter is operated to sample the oscillator frequency or period and the count achieved is applied as a preset reference to a second down counter which is counted down in one sample period while a fresh count value is being established in the first counter. The residue in the second counter at the end of a sample period is examined by detection logic to determine the presence of a vehicle. Preferably the first counter is updated every Nth sample period whereas the second counter is activated every sample period. Upon vehicle detection the first counter is frozen at the value preceding detection, the second counter continuing operation.

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 vehicle presence detection system capable of detecting multiple entry and exiting comprising an electrical signal generating system comprising a tuned circuit having a magnetic field-producing induction loop for receiving a vehicle in proximity thereto to change the field configuration and corresponding signal resulting therefrom. Signals generated by said loop result from changes in the field of said loop and occur as a result of the entrance or exiting of a vehicle into or away from the proximity of the loop. A first or signal amplifier is used for amplification of the signal received from said loop. A second amplifier responds to positive or negative polarity input from said first amplifier to provide an output in response to a rapidly changing input which will activate a logic gate for sensing the polarity of said second amplifier output signal and producing a gated output signal.

Abstract: A vehicle detector installation includes a loop oscillator the loop of which is laid in the roadway and which is locked in operation to a voltage controlled oscillator (VCO). Vehicle detection is effected by a phase detector monitoring the phase difference between the oscillators. The VCO is incorporated in a phase-lock loop (PLL) that is capable of locking to a multiple of a reference frequency oscillator over a range of multiples. To achieve the locking of the loop oscillator to the VCO, means are provided for disabling the normal operation of the PLL and sweeping the VCO over its range of frequency until the phase detector indicates that the loop oscillator and VCO frequencies are equal. This indication activates the PLL to its normal operation to pull the VCO and therewith the loop oscillator to an adjacent multiple of the reference frequency. The PLL is maintained by a repeated charge/discharge cycle of the VCO capacitor that is dependent on the phase of the reference oscillator and the VCO.

Abstract: A convertor is used having an impedance responsive to the magnetic field intensity of the earth. The convertor may be coupled to a detector for monitoring the impedance of the convertor and generating a call signal responsive to the change in impedance. Generally, the impedance is primarily inductance and the detector is an oscillator using the convertor in a resonant circuit with a frequency monitor coupled to the detector. The convertor is an open magnetic structure having a non-linear BH curve biased by the earth's magnetic field. The open magnetic structure is a core of a highly permeable material which approaches saturation under the influence of the earth's magnetic field, with the axis of the core at least partially aligned with the magnetic flux lines of the earth's magnetic field, and a coil wound around the axis of the core.

Abstract: A circuit used in a traffic control apparatus for detecting changes in the frequency of an oscillator which has an inductive loop-sensor as a resonating element. The circuit comprises a phase-locked loop oscillator with restricted tuning range and a high impedance amplifier followed by threshold detectors adjusted to sense the entry and exit of a vehicle over the area covered by the loop-sensor. The high-resolution of the circuit overcomes long-term drift problems inherent to loop-sensor detectors with analog circuitry.