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: Traffic measurement equipment has a pair of coaxial cables having barium titanate piezo-electric responsive crystals embedded in the polymer together with a vehicle presence detector to indicate all measurements required of traffic including vehicle count, vehicle length, vehicle time of arrival, vehicle speed in any required measure, number of axles per vehicle, axle distance per vehicle, vehicle gap, headway and axle weights.

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: 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: 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: 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 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.