Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1988-10-25
1990-07-10
Willis, Davis L.
Optics: measuring and testing
By particle light scattering
With photocell detection
G01N 2153
Patent
active
049403273
ABSTRACT:
A real time asbestos aerosol monitor and method are provided. An ambient air sample is passed through a first sensing zone where fibers in the sample are electrically aligned and oscillated as they are illuminated perpendicular to the fiber axes with high intensity laser light. The scattered light signal pulse train from a first detector is analyzed to determine the presence and size of fibers in the sample. The air sample is then passed through a second sensing zone including a hybrid electric/magnetic field to electrically align and magnetically oscillate asbestos fibers. The sample in the second sensing zone is illuminated perpendicular to the fiber axes, with the scattered light signal pulse train from a second detector being analyzed to determine whether each fiber detected in the first sensing zone is an asbestos fiber. Advantageously, clean air is circulated across illumination optical surfaces to protect against abrasive elements in the air sample. Zeroing and calibration are also provided.
REFERENCES:
patent: 3692412 (1972-09-01), Chubb
"Rotational Electrodynamics of Airborne Fibers", Lilienfeld, J. Aerosol. Sci., vol. 16, No. 4, pp. 315-322, (1985).
"Light Scattering from Oscillating Fibers at Normal Incidence", Lilienfeld, J. Aerosol. Sci., vol. 18, No. 4, pp. 389-400, (1987).
"Alignment of Respirable Asbestos Fibers by Magnetic Fields", Timbrell, Ann. Occup. Hyg., vol. 18, p. 299, (1975).
"Rapid Screening for Detection of Asbestos Fibers in Water Samples", Chatfield and Riis, EPA-600/4-83-041, Sep. 1983.
MIE Fibrous Aerosol Monitor, Model FAM-1 User's Manual, MIE, Inc., 213 Burlington Road, Bedford, Mass. 01730, Aug. 1988.
Diagram entitled "FAM-1 Optics-Flow Diagram".
Diagram entitled "Optical Configuration of Fibrous Aerosol Monitor".
Diagram entitled "Quadrupole electric field configuration and optical detection geometry of GCA Fibrous Aerosol Monitor model FAM-1".
Koren Matthew W.
TRC Companies Inc.
Willis Davis L.
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