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Apparatus for correcting theodolites

  • US 4,136,955 A
  • Filed: 08/27/1976
  • Issued: 01/30/1979
  • Est. Priority Date: 09/02/1975
  • Status: Expired due to Term
First Claim
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1. Apparatus for providing a relative measure of horizontal and vertical angles between first and second directions, comprising means to aim in said first and second directions, means to generate a periodic moire pattern with a relative position corresponding to the direction of said aiming means, four photoelectric receivers in line for sensing the relative position of said moire pattern, each of said receivers covering one fourth of one moire period and providing one signal of two pairs of electrical output signals in push-pull relationship, two differential amplifier means each connected to one of said push-pull output pairs, the differential output signals being in phase quadrature, a clock oscillator means having two output signals of corresponding phase quadrature, signal multiplier means, multiplying each differential output signal with one of the clock signals, forming two product signals, signal adding means, forming the sum of the two product signals and a phase meter for determining the phase difference between the output of said signal adding means and one of the clock signals, said phase difference being indicative of the relative position of said periodic moire pattern and of the direction of said aiming means.

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