| 摘要 |
PURPOSE: To monitor the quality of a fuel gas or other process gases by a method wherein a light beam is emitted to an inner flow part from a light source arranged within a housing, a first photodetector and a second photodetector which are positioned within the housing detect total intensities and base line levels of the light beam, and the ratio of the intensities is found. CONSTITUTION: A light beam 110 is emitted to an inner flow part 112 from a light source 104 which is positioned within a housing 102, A photodetector 106 is arranged so as to face the light source 104, and a photodetector 108 is arranged so as to be adjacent to a position which is deviated from the photodetector 106 in a range of about 10° to 60° in an angle direction. When particles or other interfering substances do not exist in a gas flow which is moved in the inner flow part 112, the photodetector 108 detects the baseline level of light reflected from the photodetector 106 and the Rayleigh scattering of the light from gas molecules in the flow, Then, when the particles or the like exist, the amount of the existing particles is found by a circuit 114 on the basis of the ratio of the total light intensity of the light detected by the photodetector 106 to the light intensity of the light detected by the photodetector 108.
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