Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1990-12-20
1993-05-04
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
250214B, H01J 4014
Patent
active
052084523
ABSTRACT:
The present invention provides a photodetection apparatus having such an arrangement that when signals from the light receiving means in the photodetection device are sampled at a frequency substantially equal to the lowest frequency at which the source of pulse rays is lighted on, one of the noise signal I.sub.nc due to the pulsed illumination as from the fluorescent lamp and the normal output signal I.sub.sc from the laser beam necessarily presents for each of the sampling periods. In the preferred forms, output signal values sampled in the number of cycles corresponding to at least three times the sampling period are compared with each other. If it is judged that one output signal is larger than the other two output signals which are substantially equal to each other, it is determined that the one output signal is a normal output signal I.sub.sc from the laser beam. The one output signal is then taken for the subsequent signal processing step. In the other case, all the output signals are determined to be noise signals from disturbance rays as from the fluorescent lamp, including AC components and will not be taken for the subsequent signal processing step. In such a manner, any adverse affection due to the pulsed AC rays can be eliminated.
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Allen Stephone B.
Kabushiki Kaisha Topcon
Nelms David C.
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