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.
A method and apparatus is provided for determining if a vehicle with an operating engine is at a particular location, the apparatus comprising: an antenna comprising a continuous wire formed into at least one loop; and a means to determine when the antenna is exposed to an oscillating electromagnetic field having a frequency between about 700 and about 2100 Hz of a strength characteristic of a vehicle's alternator operating in the vicinity of the antenna. In a preferred embodiment of the present invention, the sensor of the present invention further comprises a means to generate a signal when the antenna is exposed to the oscillating electromagnetic field having a frequency between about 700 and about 2100 Hz of a strength characteristic of a vehicle's alternator operating in the vicinity of the antenna, and the signal is used as an input into a logic system that requires that the signal not be generated in order for a refuelling system to refuel a vehicle in the vicinity of the antenna. The antenna is preferably a figure eight loop antenna placed in pavement below the location at which the vehicle is expected to be. The sensor of the present invention is particularly applicable as a input to disenable a fuel pump at a refuelling station.
An inductive loop sensor for detecting vehicles travelling along a lane of a roadway comprises a figure-of-eight conducting loop. The loop is arranged with its three segments transversely across the roadway to detect the wheels of vehicles travelling along the roadway. The length of the loop in the direction of travel along the roadway is less than 60 cms. Traffic monitoring apparatus energises the loops and detects the passage of vehicle wheels over the loops to provide for the classification of vehicles by axle count.
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.
A passive detection system for a levitated vehicle includes track circuits. Each track circuit includes a detection loop having a cable with a first end, a length and a second end. The track circuit also includes a transmitter electrically connected to the first end of the cable and adapted to source a current to the detection loop, and a receiver electrically connected to the second end of the cable and adapted to sense the current from the detection loop. An inductor core includes two openings adapted to receive the length of the cable and two openings adapted to avoid the first and second ends of the cable. The inductor core is adapted to change the sensed current of the receiver, in order to detect a presence of the levitated vehicle at the detection loop. A member is adapted to support the inductor core from the vehicle.
Loop sensing apparatus for detecting vehicles traveling along a lane of a roadway comprises an outer loop producing a region of magnetic field with the same polarity and an inner loop sized to fit within this region of constant polarity. The inner loop provides two regions of opposite polarity, so that field produced by the outer loop has a null effect on the inner loop. Detection circuitry energizes both the outer and inner loops individually for separate detection of vehicles passing over the loops.
