Optical measurement systems often need to detect the positions of plural light spots illuminated by various types of light sources. The applications using these systems usually require the measurement performance to be fast, of high accuracy and capable of simultaneously detecting plural points. In this paper, we propose a new method for the measurement of plural light-spot positions that satisfies all three of the requirements listed above. The basic principle of the method is to detect which of the sensor elements produces the peak value and to calculate the actual peak positions of the light spot by employing an analogue interpolating circuit. We have designed and built a prototype position-sensor system that implements the proposed method. The experimental results are as follows: (i) the relative error is at most 1.6%; (ii) the sampling time is 9.5 µs times the number of detected spots; and (iii) the proposed method is insensitive to background light. In addition, with this method one can measure other properties with physical spot-like positions such as pressure and ultrasound.
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