Development and Testing of an Optical Extinction Probe for Measuring Lofted Dust Flow Densities.

An optical extinction probe for measuring the mass concentration of dust lofted in high explosive field tests and shock tube experiments was designed and tested. Low cost optical components provide the necessary optical dynamic range for measuring mass concentration from 10 to the minus fourth power to 10 to the minus second power gm/cm to the third power. Fiber optics carry the light signal to the measurement points so that the electro-optics can be placed out of the blast environment. Tests using a laboratory version of the probe and representative dust samples demonstrated that the probe could make repeatable measurements in the range of 10 to the minus fourth power to 10 to the minus second power gm/cm to the third power. Laboratory tests also demonstrated that the measurement range could be varied by changing the optical path length. Information obtained from an independent service laboratory confirmed that the probe calibration curves scaled to the particle size distribution information differed from measurements made in the calibration tests by up to 75%. Based on the findings of this program it is recommended that the optical probe be characterized by direct calibration rather than calculated from particle size distribution information. A prototype measurement station was designed to withstand ideal and precursed shock with peak overpressures up to 100 psi.