Multiple pathlength sensor for determining small particle size

Abstract

A multiple pathlength sensor is disclosed that is installed substantially within a process stream containing particles at high concentrations. The sensor includes a transparent surface for receiving the first and the second light energy emissions projected by first and second light delivery arrangements. The first and second light energy emissions penetrate the transparent surface and enter the sensor in a first directional path. A first light deflecting surface modifies the first and second light energy emissions to travel into a second directional path through the sensor. A first passage exposed to the process stream is sized to receive particles of a first predetermined size range. The first light energy emission in the second directional path is projected through the first passage to irradiate the particle ensemble therein. A second passage exposed to the process stream is sized to receive particles of a second predetermined size range. The second light energy emission in the second directional path is projected through the second passage to irradiate the particle ensemble therein. A second light deflecting surface receives the light energy projected through the first and second passages and the light energy scattered by the particle ensemble in each of the first and said second passages. The second deflecting surface directionally modifies the light energy it receives to follow a third directional path through the sensor to the transparent surface, where the light energy escapes the sensor and is collected by a light collection arrangement.