Automated Analyzer for Particle Size and Shape Distribution Developed
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TECHNOLOGY ADVANCES Automated Analyzer for Particle Size and Shape Distribution Developed An automated testing system that uses the novel concept of digital image analysis of free-falling particles to measure particle size, shape, and distribution has been developed at Clarkson University and the University of Tennessee, Knoxville. The automated PSDA system, shown in Figure 1, was specifically developed to measure particle size distribution over a wide range for materials that do not cohere and have equivalent diameters that fall in the range of 25 µm to 60 mm. This system has four major components: (1) particle-sizing hardware and software, (2) an optical lens system driven by a stepper motor, (3) a horizontal vibrating feeder, and (4) an appropriate lighting system. A progressive-scan, charge-coupled device (CCD) camera with a computercontrolled optical system that has a large range of magnification is used to obtain high-contrast, two-dimensional digital images of free-falling particles. The vibrating feeder causes the material to flow and free-fall in front of the lens. The feeder is adjusted to obtain images of individual particles projected onto the image plane. Custom-developed application software continuously records the images of particles for analysis in real time. Software then counts the particles in each image, using a specified intensity threshold, and measures the size, shape, and various other features of each particle. A graphic interface is used to display the updated measurement results for real-time analysis and control. After obtaining information from a number of particles, convergence of the measured size distribution is evaluated. The analysis automatically stops once statistically admissible results are obtained on the sample being tested. Output data such as the particle size distribution curve and shape information are displayed in real time throughout the analysis, as shown in Figure 2. In many industries, particle size distribu-
tions above 50 µm are obtained by sieve analysis, which produces a weight-based size distribution curve. Among the advantages of using PSDA for this application
Figure 1. Automated laboratory particle size and shape distribution analyzer.
are that it is automated and has a relatively low cost, it eliminates the noise and vibration often associated with sieve analysis, and it provides particle shape information plus the grain size distribution representative of the sample in a short period of time. Since the PSDA technique uses area-based measurements from twodimensional images, techniques have been developed to translate this information into volume/weight-based results. The size distribution of various types of materials compares well with traditional sieveanalysis data of the same materials. For refractory and abrasive materials, information about particle shape and texture is important. PSDA technology can provide statistically admissible shape information (e.g., roundness, aspect ratio). For applications related to flow behavior and particle degradation
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