The report describes the design and performance of an instrument, based on the concept of instantaneous intensity ratio, for measuring particle size distributions of dense particulate matter. The method involves simultaneously measuring the intensity of light scattered by a particle at two small angles, and then taking their ratio. The ratio depends on particle size, but has minimal dependence on refractive index. By using a pulse height analyzer as the display device, particle size distribution changes can be detected rapidly. Thus in situ, real-time monitoring of size distributions can be achieved. The instrument allows more than one particle in the focal volume at any instant and selects the scattered light pulses randomly for processing, enabling dense particulate matter to be sized accurately. The concept is discussed. The instrument's detailed design features are presented. Calibration has been performed using monodisperse aerosols of accurately known diameter. The effect of refractive index is investigated, and the performance and limitations of the instrument are discussed. It is shown that, by incorporating the concept of random selection of input pulses, the concentration handling capacity is improved by an order of magnitude.

Prepared under grant no. R803532-01-0, ROAP no. 21ADL-018, program element no. 1ABO12. Issued Jan. 1977. Includes bibliographical references.