| 摘要 |
1,139,272. Road traffic detectors. LABORATORY FOR ELECTRONICS Inc. 5 April, 1967 [20 May, 1966], No. 15563/67. Heading G4Q. [Also in Divisions H3 and H4] In an ultrasonic vehicle-detector a transmitted ultrasonic pulse is generated by passing the output of a continuously running oscillator through a gated amplifier to a transducer, and echoes from a vehicle within a selected range are detected in a receiver amplifier gated off during transmission and then gated on by a " range period " pulse. In the embodiment of Figs. 3 and 4 the pulse repetition rate is controlled by free-running multivibrator 20. Continuously running oscillator 24 supplies 19kc. signals through amplifier stages 23, 25, 26, 27, 28 to a transmitting/receiving transducer located over or at the side of a roadway, the output of stage 23 being normally clamped by shunt transistor 58 but being unclamped when a pulse from multivibrator 20 switches transistor 58 off. Capacitors 59, 69 give an appreciable rise and fall time to the envelope of the resulting 19kc. pulse train and this, together with the selection of equal ohmic values for resistors 63, 65, eliminates " key clicks " by preventing large D.C. voltage changes on coupling capacitor 84. Returned echo signals pass through limiter 31 and a tuned amplifier comprising stages 32, 33, 34 to a range gate 35, 36, 37 which is blocked during transmission and is opened under the control of multivibrator 20 a predetermined time after transmission. The gated echo signals switch stages 39, 40 to actuate lamp and relay drive circuits 42, 43, 44 for indicating the presence of a vehicle and actuating a vehicle counter or traffic control system. Details of the operation of the Fig. 4 circuitry are given. In various modifications more than one transmitter/ receiver unit may be used with a single 19kc. pulse modulator (stages 20 to 26) or separate transmitting and receiving transducers may be used.
|
