| 摘要 |
A device for accurately measuring a dimension associated with a remote object without contacting the object itself is disclosed. A beam of light is directed at a surface of the object and a reflected portion of the beam is detected at a photodetector element. The particular dimension of the object is determined mathematically by measuring the distance by which the reflected light signal is offset from a predetermined point on the photodetector which is aligned with a reference plane at the object. By the use of two heads and respective light beams and photodetectors, a remote object's thickness can also be measured. In order to compensate for the angular relationship between the object's surface and that of the photodetector, a linearizing calibration circuit is included in which preset corrections are recorded in programmable memory units. The calibration settings are determined during manufacture and correct for each normally non-linear reading at incremental distances within a prescribed measurement range. Further accuracy of the system is obtained by using a high frequency sampling circuit to modulate the light source, with a demodulating circuit serving to discriminate between the input light beam and extraneous ambient light signals.
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