| 摘要 |
A device for measuring the distance to a surface comprising first and second energy emitting sources positioned at two different distances with respect to the surface and driven by a signal which is of common frequency, but which is of different phase from one another. The beams produced by the two energy sources are reflected from the surface and the resultant vector sum of the beams received by an energy responsive detector is used to produce a resultant signal which has a phase that varies with the distance to the remote surface.
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