Apparatus for detecting fibrous particle sizes by detecting scattered light at different angles
AssigneeVG Instruments Group Limited
InventorsNigel P. Smith, Neil A. Downie
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Abstract
The invention comprises apparatus capable of unambiguous determination of the length and diameter of fibrous particles, especially asbestos fibres, based on near-forward scattering of light by fibres aligned in a hydrodynamically focused gas flow. Three portions of scattered light are detected, two portions perpendicular to the fibre axis and one aligned with it, from which length and diameter can be independently determined. This independence is achieved by allowing only selected parts of the light scattered within certain selected ranges of angles to reach each detector. A two-detector instrument capable of accurate determination of fibre diameter is also described.
Claims23
Apparatus for determining the size of fibrous particles, said apparatus comprising:
- (1) means for generating at least one beam of radiation passing through a sensing volume;
- (2) means for aligning said fibrous particles and passing them in single file along an axis intersecting said beam in said sensing volume;
- (3) first, second, and third radiation detecting means, each having an output substantially proportional to the intensity of the radiation falling on it, respectively disposed to receive first, second and third portions of radiation scattered by said fibrous particles in near forward directions;
- said first portion comprising radiation scattered within a first range of angles to said beam and passing through a first area on a plane perpendicularly disposed to said beam, said first area including the orthogonal projection of said axis on said plane;
- said second portion comprising radiation scattered within a second range of angles to said beam and passing through a second area on said plane which includes the perpendicular in said plane to said orthogonal projection;
- said third portion comprising radiation scattered within a third range of angles to said beam and passing through a third area on said plane which includes the perpendicular in said plane to said orthogonal projection, the angles included in said third range being greater than those included in said second range;
- and
- (4) means for combining the outputs of said first, second, and third radiation detecting means to obtain information on the size and shape of said fibrous particles.
Apparatus for determining the diameter of fibrous particles comprising:
- (1) means for generating at least one beam of radiation passing through a sensing volume;
- (2) means for aligning said fibrous particles and passing them in single file along an axis intersecting said beam in said sensing volume;
- and
- (3) first and second radiation detecting means, each having an output substantially proportional to the intensity of radiation incident upon it, respectively disposed to receive first and second portions of the radiation scattered in near forward directions by said fibrous particles;
- said first portion comprising radiation scattered within a first range of angles to said beam and passing through a first area on a plane perpendicularly disposed to said beam, said first area including the perpendicular to the orthogonal projection of said axis on said plane;
- said second portion comprising radiation scattered within a second range of angles to said beam and passing through a second area on said plane, said second area including the perpendicular to the orthogonal projection of said axis on said plane and the angles included in said second range being greater than those included in said first range;
- the improvement comprising limiting the extent of said first and second areas in a direction perpendicular to said perpendicular to the orthogonal projection to ensure that the ratio of the outputs of said first and second detecting means is substantially independent of the length of said fibrous particles up to a selected maximum length.
Dependencies are inferred from the claim text.