GB1520074A - Vehicle presence detector - Google Patents

Abstract

1520074 Vehicle presence detector SPETSIAL KONSTRUKTOR BJURO PROMYSHLEN AVTOMATIKI 29 March 1976 12520/76 Heading G1N [Also in Division G4] In a vehicle presence detector, the output of signal generator 1 being fed directly; and via resonance amplifier 2 including loop 4 buried beneath a roadway surface; to phase sensitive converter 5 whose output is altered by the presence or otherwise of a vehicle adjacent the loop 4, the converter output undergoing differentiation to provide signals operating a threshold device 8 whose output, Figs. 2d, 3d (not shown) passes to device 9, the differentiation is performed by arrangement 7, 10-13, wherein the converter output is fed to each of three or more differentiators 7, 10, 11 of distinct time constants, the differentiating networks being associated with the inverting input of the amplifiers, the direct inputs, used for linear amplification, of amplifiers 10, 7 receiving via converters 12, 13, the outputs of amplifiers 11, 10 respectively. The spread of differentiator time constants, amplifier 7 differentiating the type of signal produced by a low speed vehicle, amplifier 11 differentiating the type of signal produced at the highest vehicle speed, enables reliable detection over a wide vehicle speed range. The threshold circuit has hysteresis, being triggered at the distinct levels (18, 23) Figs. 2c, 3c (not shown). Unit 6 functions as an integrator, preventing transmission of short, noise pulses. The detector is part of a traffic control, or investigation, system.