Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1989-05-19
1991-04-30
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356343, G01N 1507, G01N 2149
Patent
active
050121197
ABSTRACT:
A method and apparatus for determining the amount and size of particles and bubbles in a liquid process medium. The invention comprises the steps of providing a collimated light source to generate a light beam of a known wavelength, and directing it to illuminate a liquid sampling volume within a cell positioned within a sensor housing constructed to collect the light scattered by particles and/or bubbles within the sample caused by the impingement of the light beam. The scattered light is then separated into forward, and/or right angle and back scattering portions, and converted into separate electrical signals for each scatter direction. Since the scattering coefficient is a direct function of the density of the sampling volume, the presence of bubbles reduces the density and the amount of radiation scattered in the backward direction. Using the level of scattering resulting from the liquid medium alone as a reference, particles and bubbles within the sampling volume each scatter radiation at a level that results in significant and substantially similar positive signals in the forward and/or right angle scattered channels. As a result bubbles and particles are not distinguishable in the forward or right angle scatter channels. Heretofore it has been known that back scattering exists in sample volumes containing bubbles and particles, however the presence and amount of the back scattering has not been correlated to the presence or absence of bubbles. In this invention it has been found that in contrast to the forward and/or right angle scattering characteristics, the presence of bubbles within the sampling volume results in a significant negative signal in the back scatter channel while on the otherhand the presence of particles within the sampling volume results in only a small positive signal in the back scatter channel. This difference in the scattering characteristics of bubbles and particles permits the separate signals from both forward and/or right angle scattering and back scattering to be processed to determine the size and quantity of particles and/or bubbles relative to the medium being monitored.
REFERENCES:
patent: 4419903 (1983-12-01), Jackson
patent: 4662749 (1987-05-01), Hatton et al.
Nelms David C.
Oen William L.
Xinix, Inc.
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