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Phase-Sensitive Detector (PSD) measurement
PSD method based on the same method which is used for focusing in SLR cameras. The light is divided with beam splitter in two rays and then by comparing the two rays' phase the distance can be measured. There is movable lens and its position is known.
Figure 2: Distance measurement with PSD.Figures 1 to 4 represent conditions where the lens is focused (1) too near, (2) correctly, (3) too far and (4) much too far.
PSD method is similar to CMOS but PSD is more accurate only matte or specular surfaces. While with CMOS one can choose the brightest pixel to be the center of the laser beam but with PSD the beam centroid is determined by whole reflected dot. If reflective surface is rough, the beam spreads quite large area and distance is calculated inaccurately. So PSD method suites well for example surveying where one need to use some specular stick anyway at the other end. However, that method is not so good for universal laser meter which is usually used with various materials which are often quite rough.
Figure 2 illustrates how different methods differ from each other. Of course this is the worst case scenario what can happen in certain conditions.
Figure 23: Accuracy comparison between PSD and CMOS
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Pulsed time-of-flight measurement
Figure 34: Basic principle of time-of-flight (TOF) measurement
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