Parameter selection for correlation-based particle velocity sensors

Two optical sensors were developed to measure velocities of glass beads, soybeans, and chopped wheat straw Velocities were determined using a cross-correlation method derived through fast Fourier transformations. Optimum sampling frequencies and sample sizes within different velocity ranges were determined for real-time velocity measurements. Statistical analysis showed that the optimum sample size is determined mainly by the size and type of the particles. For the glass beads, soybeans, and chopped wheat straw the optimum sample sizes were 512, 128, and 256, respectively. Once the sample size is determined the optimum sampling frequency can be determined based on the range of velocity to be measured With the optimum measurement parameters selected, the measurement errors can be limited within 5%, 6%, and 3% for glass beads, soybeans, and chopped wheat straw, respectively. This method is insensitive to particle shape and color For real-time measurement, digital signal processing using the fast Fourier transformation method is recommended.