| 摘要 |
PURPOSE:To eliminate error due to speckle in illuminance even for an object irradiated with light from an AC illuminator and solar beam by correcting an optoelectric converted output by means of a reference signal synchronized with flickering of the AC illuminator. CONSTITUTION:When an object is illuminated by a fluorescent lamp, for example, an optoelectric conversion element 4 produces a signal corresponding to flickering of the fluorescent lamp, i.e., a signal having frequency 2f two times as high as the power supply frequency f, and the signal is delivered as a reference signal to a phase detecting circuit 5. A band-pass filter 3 is set at a frequency band of 2f+ or -DELTAf and passes only the frequency two times as high as the power supply frequency or thereabout. Output signal from the filter 3 is subjected to phase detection using the output signal from the element 4 as a reference signal. The signal subjected to phase detection is fed to the filter 3 where only required signal is extracted thus obtaining a spatial filter output which is not susceptible to solar beam. The spatial filter output is converted through an A/D converter 7 into a digital signal which is then fed to an operation processing circuit 8 where the extent of congestion is operated and delivered to the outside through an output circuit 9. |
