| 摘要 |
PURPOSE:To make it possible to prevent the light reflected from materials except dust from entering a photodetecting part by arranging a measuring device in such a way that the light beam projected from a light emitting part toward directions except a desired direction are shut off by a partition plate and the light beam incident to a photodetecting part from directions except the desired direction are shut off by a partition plate. CONSTITUTION:Clean gas is supplied into a measuring chamber 15 and after said chamber is cleaned by the clean gas, the gas to be measured including dust is supplied therein and when the supply is stabilized, a light beam is projected from a light emitting part 4 to the gas to be measured between partition plates 16 and 18. The direct light is made incident to a photodetecting part 8 for direct light and the scattered light is made incident to a photodetecting part 10. The outputs from both parts 8, 10 are inputted through amplifiers 11, 12 to an arithmetic circuit 13, by which dust density is determined and is stored. The supply of the gas to be measured is stopped after the measurement of the dust density. The clean gas is then supplied to the chamber 15 and after the chamber is cleaned by said gas, the light beam is projected from the part 4 to the clean gas between the plates 16 and 18. The light beam past the clean gas enters the part 8 and the output thereof is inputted to the circuit 13 which detects the dust density by the difference from the previous value. |
