ES8404746A1 - Forward scattering laser particulate sensor - Google Patents

Abstract

The sensor is used to monitor the level of particulates flowing through a large dia. pipe, e.g. in the catalyst dump at a petroleum cracking plant. A laser light source directs a beam across the flow. A lens collects light scattered along a certain axis from a sample volume within the gas flow. A photodetector receives light focussed by the lens to provide a proportional output signal. A second photodetector receives light from the source to provide a second, proportional, output signal. - A threshold level detector responsive to these output signals provides an indication of particulate level exceeding the desired maximum. A cylindrical mounting is attached radially outward from opposite sides of a pipe through which the gas flows. Each mounting opens at its inner end to the interior of the gas pipe, with a transparent window at each outward end. (0/3) EPAB- EP-108799 B A sensor for monitoring the level of particulates in a gas flow comprising: a laser (12) positioned to direct a beam of light across said gas flow (10); a first lens (18) for collecting light scattered along a certain axis from a sample volume (16) located within said gas flow (10); a first photodetector (22) positioned to receive a light focused thereon by said first lens (18), for providing a first detector output signal proportional thereto; a second photodetector (30) positioned to receive light energy from said laser (12) for providing a second detector output signal proportional thereto; and a threshold detector (64,70) responsive to the first detector output signal and the second detector output signal for providing an output signal indicating when the particulate level in said sample volume exceeds a predetermined level, characterised in that: said first lens (18) produces by means of scattered light an image of the beam cross section at the centre of said sample volume on said first photodetector (22) matching the radius (h) of the beam cross section to the detector radius (r), an annular stop (20) is located within said beam of light between said first lens (18) and said second photodetector (30) and has a central aperture and an annular aperture surrounding said central aperture and being sized to define limits of said sample volume in the direction of said beam of light; said second photodetector (30) is positioned between said first lens (18) and said first photodetector; and a second lens (28) is positioned within said central aperture of said annular stop (20) for focusing said light energy from said laser (12) onto said second photodetecor (30). (10pp) - EP-108799 B A sensor for monitoring the level of particulates in a gas flow comprising: a laser (12) positioned to direct a beam of light across said gas flow (10); a first lens (18) for collecting light scattered along a certain axis from a sample volume (16) located within said gas flow (10); a first photodetector (22) positioned to receive a light focused thereon by said first lens (18), for providing a first detector output signal proportional thereto; a second photodetector (30) positioned to receive light energy from said laser (12) for providing a second detector output signal proportional thereto; and a threshold detector (64,70) responsive to the first detector output signal and the second detector output signal for providing an output signal indicating when the particulate level in said sample volume exceeds a predetermined level, characterised in that: said first lens (18) produces by means of scattered light an image of the beam cross section at the centre of said sample volume on said first photodetector (22) matching the radius (h) of the beam cross section to the detector radius (r), an annular stop (20) is located within said beam of light between said first lens (18) and said second photodetector (30) and has a central aperture and an annular aperture surrounding said central aperture and being sized to define limits of said sample volume in the direction of said beam of light; said second photodetector (30) is positioned between said first lens (18) and said first photodetector; and a second lens (28) is positioned within said central aperture of said annular stop (20) for focusing said light energy from said laser (12) onto said second photodetector (30).