GB1294874A - - Google Patents

Abstract

1294874 Optical distance measuring CARROL & REED Ltd 18 Aug 1970 [3 Sept 1969] 43696/69 Heading H4D [Also in Division G4] Although the claims relate to a general method of determining the phase difference between two signals of equal frequency, the only described embodiment relates to a pulsed light radar, wherein a quartz oscillator 10, Fig. 1, feeds a 10MH 3 signal to a "by 20" divider 11. to give a 500KH 3 signal. This, after squaring at 13, modulates the output of GaAs photo dicde 14 such that pulses of light at 500K.p.p.s. are directed towards and reflected by remote reflector 15. The reflected pulses are detected at receiver 16 and the modulation at 500K.p.p.s. is fed to one input of a summing device 25. The summing device is a mixer and receives at its other input a signal at 499À9K.H 3 produced by a series of frequency dividers and mixers 17-23 from the output of oscillator 10. The output of the summing device 25 thus contains a component at 100H 3 which is separated out by filter 31 and squared off by zero cross detector 33 to give waveform 36, Fig. 3. -Part of the 500KH 3 signal from divider 11 is similarly processed in chains 24, 26, 28, 30, 32 to give 100H 3 waveform 35a, Fig. 2. The phase difference between waveforms 35a and 36 is proportional to the distance of the reflector 15 and is indicated by a digital phase comparator 37 receiving the waveforms and yielding "non- overlap" waveforms 38, Fig. 4, having pulses of width W indicative of said distance. A pulse signal at 10MH 3 from oscillator 10 is fed to gate 39 together with waveforms 38 to give the series of pulse bursts 40, Fig. 5, each burst having a number of pulses indicative of said distance. A digital counter and display 41 determines this number and . displays it as a distance. The system is zeroed by variable phase shifter 45 and calibrated by offset control 46. Gain control of the receiver 16 by level control 34a receiving the output of filter 31 ensures the correct amplitude of waveform 35a. By changing the frequency ratio of the signals applied to gate 39, a direct readout in 41 in degrees or radians is possible.