Method and apparatus for electrooptical distance measurement
First Claim
1. A method for electrooptical distance measurement, whereby a beam of modulated light is transmitted over the distance and after reception is converted into an electrical signal corresponding to the modulation of light, said signal being compared with respect to time with reference signal used for modulating the light beam, at least one of said signals being shifted with respect to the other one until a given time relation between the signals is reached, and the distance being found from the extent of said signal shift, comprising the steps(a) mixing for temporal comparison the signal converted from the modulated light and the reference signal used for modulating the light beam,(b) time-shifting the reference signal by means of a control circuit and a driving signal obtained from said mixing step, until a given time relation with respect to the converted signal is reached,(c) frequency converting to a lower frequency the shifted as well as the unshifted reference signals, and(d) measuring the temporal difference of the frequency-converted reference signals to determine the temporal shift of the reference signal obtained in said time-shifting step.
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Abstract
With an electrooptical distance meter a reference signal is timeshifted by means of an electronic phase shifter (20), until it has a given phase relation to the measurement signal. Both signals are compared in phase by a double balanced mixer (22), the output of which directs the electronic phase shifter (20) by a control loop (20, 22, 23). The phase shift is measured after frequency conversion by two additional double balanced mixers (24, 25). Thus handy precision distance meters with measurement frequencies about 500 MHz may be built, comprising control loops for laser diode transmitter (1), avalanche diode receiver (13), phase shifter (20) and intermediate frequency, as well as a processor (5, 29) control for automatic function of the instrument.
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Citations
17 Claims
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1. A method for electrooptical distance measurement, whereby a beam of modulated light is transmitted over the distance and after reception is converted into an electrical signal corresponding to the modulation of light, said signal being compared with respect to time with reference signal used for modulating the light beam, at least one of said signals being shifted with respect to the other one until a given time relation between the signals is reached, and the distance being found from the extent of said signal shift, comprising the steps
(a) mixing for temporal comparison the signal converted from the modulated light and the reference signal used for modulating the light beam, (b) time-shifting the reference signal by means of a control circuit and a driving signal obtained from said mixing step, until a given time relation with respect to the converted signal is reached, (c) frequency converting to a lower frequency the shifted as well as the unshifted reference signals, and (d) measuring the temporal difference of the frequency-converted reference signals to determine the temporal shift of the reference signal obtained in said time-shifting step.
- 3. An apparatus for electrooptical distance measurement with a means for transmitting continuously modulated light, a receiving means for converting said modulated light into an electrical signal corresponding to the modulation of light, as well as a means for comparing, with respect to time, said converted signal with a reference signal used for modulating said light transmitting means, means for changing by a measurable amount the temporal shift between said converted signal and reference signal including means for obtaining the distance from said measured temporal signal shift, the apparatus comprising a first double balanced mixer (22) for temporal comparison of converted signal and reference signal, an electronic phase shifter (20) for time-shifting the reference signal, a local oscillator (27) and two double balanced mixers (24, 25) for frequency-converting respectively the shifted and the unshifted reference signals, as well as a phase meter (28) for the frequency-converted reference signals.
Specification