| 摘要 |
1,183,640. Vehicle detectors. GRUNDIG E.M.V. ELEKTRO-MECHANISCHE VERSUCHSANSTALT Inh. MAX GRUNDIG. 10 Nov., 1967 [10 Nov., 1966], No. 51320/67. Heading G4Q. [Also in Division G1] A synchronous demodulator for demodulating an alternating signal U<SP>1</SP> obtained by detection of a fluctuating light beam comprises a photoelectric switch 1 which is illuminated by light modulated in synchronism with the fluctuating light beam. The capacitor 4 is thus charged to a positive or negative D.C. voltage U through load resistor 3. The photo-electric switch 1 may be a photoconductive cell. Since this may not respond sufficiently rapidly to provide the required phase relationship in the demodulation, a photodiode may be used, Fig. 2 (not shown). In order to remove the photo-electric voltages produced by illumination of a photodiode, two photodiodes connected in series and in opposite polarity may comprise the switch 1. Alternatively an arrangement of photodiodes 9, 9<SP>1</SP> and non-radiation responsive diodes 10, 10<SP>1</SP> are used. When unilluminated the switch is non-conductive in either direction, but on illumination it may conduct, photo-electric voltages generated in the photodiodes however being blocked by diodes 10, 10<SP>1</SP>. The apparatus may be used in vehicle detectors, the light beam modified in some way by the presence of a vehicle providing the signal U<SP>1</SP> and the light illuminating switch 1, being light unaffected by the vehicle. |
