| 摘要 |
PURPOSE:To avoid the measuring error caused due to misarrangement of chopper drive, by giving the output of the photodetector of the detector using optical chopper to the signal processing circuit to obtain the laser current modulation signal and applying this to the laser current source. CONSTITUTION:The light emitting element 10 and photodetector 11 are provided with the chopper blade 7 sandwiched outside the path of the laser light. The output signal of the photodetector is given to the signal processing circuit 12 together with the output signal of the infrared-ray detector 6. Thus, the laser current modulation signal of frequency in response to the revolution of the motor 8 of the chopper blade 7 is obtained, and this signal is applied to the laser current source 13 to modulate the laser current. Thus, even if the rotating speed of the motor 8 is varied, the ratio of fundamental frequency of electric signal output from the infrared-ray detector 6 and photodetector 11 is determined only with the ratio of the pitch of the through- hole pattern of the chopper blade 7 independently of the rotating speed of the chopper blade 7. |
