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Heterodyne interferometer arrangement

Image Number 4 for United States Patent #5331400.

A heterodyne interferometer arrangement comprises a two-frequency light source, an optical reference branch for producing a reference signal, an optical measuring branch, which includes an interferometer unit causing a phase rotation of the light beams in response to a length to be measured, as well as a measuring transducer arranged at the output of the interferometer unit, and a phase comparator arranged subsequent to the reference transducer and the measuring transducer. In order to minimize linearity errors, the measuring transducer comprises first and second optoelectric measuring transducer units, which respond to light components orthogonal to each other and which are followed by two phase comparators whose output signals represent phase differences between the first or the second measuring signal on the one hand and the reference signal on the other, and a mean value generation circuit whose output signal represents the mean value of the first and second phase differences. The mean value of the phase differences is virtually free from non-linearity.

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