Opto-electric target detector - has movable transparent mask fitted with grills which produce modulation of given frequency during fraction of mask movement period

摘要

The detection and location system is of the amplitude modulation type. It uses an optical circuit which receives and focusses incident radiation from an observed field. It has a movable mask fitted with transparent grills on an opaque base which passes periodically transversally over the optical axis. The periodic transversal movement produces modulation of a determined frequency during a fraction of each period of movement. The system has a photodetector element and a pass band filter which delivers a carrier at the determined frequency amplitude modulated by a signal of frequency corresponding to the period. The system has also a demodulation circuit a modulation signal filter circuit and a phase analyser circuit. The grills are distributed along a number of optical tracks (Pl-Pn) to produce as many distinct frequencies (F1-Fn) during the fraction of the movement period (TD). The pass band filter circuit (5) is of the switchable type. Its central frequency presents successively the different values of track frequency, each during a period at least equal to the transverse movement period.