Optics: measuring and testing – For size of particles – By particle light scattering
Patent
1987-11-12
1989-10-03
Rosenberger, Richard A.
Optics: measuring and testing
For size of particles
By particle light scattering
356342, 377 11, G01N 1502
Patent
active
048712515
ABSTRACT:
Apparatus for analyzing particles contained in a fluent edium (12). The apparatus includes a body (20) having a window (30), an optical source preferably comprising a laser diode (100) having a small light emitting area (140), and an optical system (102) for focusing the light from the laser diode at a focal spot (84) such that the size of the focal spot is approximately equal to the size of the light emitting area of the laser diode. A photodetector (106) is mounted in the body and detects light backscattered from the focal spot by particles in the fluent medium, and produces an electrical signal that comprises a series of pulses associated with the particles. The electrical signal is input to a detector that counts the pulses and indicates the number of particles in the fluent medium. The detector includes discrimination means for preventing the counting of a pulse that has a rise or fall time above a predetermined threshold, thereby discriminating against particles that are not at the focal spot. Means are provided for measuring the integrated amplitude of the electrical signal, and for varying the distance between the focal spot and the window to maximize such integrated amplitude. An intrinsically safe embodiment is also disclosed in which the probe positioned at the measuring site does not include any electrical components. This embodiment may be implemented using light of multiple wavelengths for characterizing individual particles.
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Diehl, S., Smith, D.T., and Sydor, M., "Analysis of Suspended Solids by Single-Particle Scattering", Applied Optics, vol. 18, no. 10, pp. 1653-1658.
Preikschat Ekhard
Preikschat Fritz K.
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