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Method and apparatus for eliminating the effects of varying sample distance on optical measurements
Method and apparatus for eliminating the effects of varying sample distance on optical measurements
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机译:消除变化的样本距离对光学测量的影响的方法和装置
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摘要
A method and apparatus for eliminating the effects of varying sample distance on optical measurements. In a first embodiment, a light source and a detector are both positioned in front of a measurement sample. A light source lens assembly focuses the light such that its focal point is behind the measurement sample, while a detector lens assembly focuses the light reflected from the measurement sample such that its focal point is in front of the measurement sample. Any movement of the measurement sample away from its nominal position does not affect the detector output because the effects of the source lens assembly and the detector lens assembly cancel each other. In a second embodiment, a light source and two detectors are positioned on one side off a measurement sample. The first detector is placed at a small angle relative to the sample normal, while the second detector is placed at a relatively large angle relative to the sample normal. A system output, which does not vary if the measurement sample is moved from its nominal position, comprises the weighted summation of the first and second detector outputs and a correction signal. The correction signal comprises a weighted difference of the first and second detector outputs.
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