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The simplest version of an intensity-based measurement system is a point detector detecting the light reflecting off of a test surface. As the surface moves farther away, the amount of detected light decreases. Such a system needs to be calibrated to the specific type of part shape and surface being detected. Detectors of this type are typically used as proximity detectors, indicating when a part is in a particular position rather than measuring the actual distance to the part itself. Light detectors of this type may also be used as vibration monitoring tools. However, they can easily be in error due to a smudge on the part unless the light level is continuously monitored by another detector to compensate.
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