Multiple wavelength instrument for measurement of particle size distributions

Apparatus for measurement of the size distribution of particles suspended in a gas or liquid comprising:

• a source of substantially collimated beam of light, said beam having a collective spectrum which consists of a plurality of substantially monochromatic light components chosen from the blue, green, and red portions of the visible light spectrum, such that at most one of said light components lies in the blue, at most one lies in the green, and at most one lies in the red;
• a lens for collecting part of the light scattered by the particles, said lens being positioned and oriented such that it does not intersect said beam;
• a set comprising a plurality of spatial filters consisting of color transparencies;
• means to present filters of said set sequentially in an image window located in the focal plane of said lens;
• a photodetector to produce a sequence of signals each of which is substantially proportional to light transmitted by a respective filter.

Apparatus for measurement of the size distribution of particles suspended in a gas or liquid comprising:

• a source of substantially collimated beam of light, said beam having a collective spectrum which consists of a plurality of substantially monochromatic light components chosen from the blue, green, and red portions of the visible light spectrum, such that at most one of said light components lies in the blue, at most one lies in the green, and at most one lies in the red;
• a lens for collecting part of the light scattered by the particles;
• a set comprising a plurality of spatial filters consisting of color transparencies;
• means to present filters of said set sequentially in an image window located in the focal plane of said lens;
• a photodetector to produce a sequence of signals each of which is substantially proportional to the light transmitted by a respective filter;
• and
• means for acting upon said sequence of signals from the photodetector by a linear transformation and using the results as coefficients in a linear combination of basis functions to yield the particle size distribution.

A method for measurement of the size distribution of particles suspended in a gas or liquid, comprising:

• passing into the particle suspension a substantially collimated beam of light, whose collective spectrum is a spectral set consisting of a plurality of substantially monochromatic light components chosen from the blue, green, and red portions of the visible light spectrum, such that at most one of the said light components lies in the blue, at most one lies in the green, and at most one lies in the red;
• with a lens collecting part of the light scattered by the particles;
• sequentially placing the members of a set of spatial filters consisting of color transparencies, one of which has uniform transmittance in an image window located in the focal plane of said lens, thereby transmitting light through said set of filters and, in the process, performing a linear transformation;
• collecting the light transmitted by each of said spatial filters sequentially by a photodetector to produce a signal substantially proportional to light transmitted by respective filters;
• acting on the resulting photodetector sequential signals by a linear transformation;
• and
• using the resulting data sequence as coefficients in a linear combination of basis functions to yield the particle size distribution.