| 摘要 |
1,099,917. Photo-electric distance measurement. SOUTH AFRICAN INVENTIONS DEVELOPMENT CORPORATION. Aug. 31, 1966 [Sept. 3, 1965], No. 38947/66. Heading H4D. In electronic distance-measuring apparatus utilizing phase comparison of the amplitude modulation of a transmitted infra-red or shorter wave and the echo, the transmitted and echo waves being demodulated to derive measuring frequency signals which are mixed with a locally generated reference frequency to provide two comparison frequency signals, the phases of which are compared to give the distance, a single mixer 19 is utilized to provide the two comparison frequency signals and a switch 17 is provided for feeding the measuring frequencies alternately to the mixer. A switch 25 may be synchronized with switch 17 to connect the mixer output to integrators 26, 27. A number of measuring frequencies may be utilized sequentially. Typical measuring and comparison frequencies are 75 Mc/s. and 10 kc/s. respectively. To allow for instabilities in oscillators 11, 24 a discriminator 23 is added. A switch 33 permits spurious phase error to be cancelled out.
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