| 摘要 |
PURPOSE:To ensure a quick compensation in a wide range for the variance of characteristics of a photodetector, by distributing a light diffusing plate plus plural polarizing plates in front of the photodetector and then giving a relative shift among these polarizing plates to control the quantity of incident rays to the photodetector. CONSTITUTION:A pair of polarizing plates 32 and 33 are provided to the light diffusing dome 31 having the light transmitting performance and provided in front of the photodetector 30. A relative rotation is given between the plates 32 and 33 so that the output voltage of photodetector 30 reaches a certain set value when a given quantity of light is irradiated to the dome 31. Thus the quantity of light passing through the polarizing plates is controlled to give a compensation to the variance of the photodetector 30. The dome 31 diffuses evenly the external beams of a wide range to irradiate them to the photodetector in the form of the beams having no direction. At the same time, these beams are diffused by the dome 31 to lose their polarizing properties. Thereafter, the light quantity is reduced again through the plates 32 and 33 to give a control to the light quantity. |
