The phase Doppler interferometry instruments measure drop size, velocity and volume flux at a point within a spray plume. These instruments provide the most detailed information of the spray characteristics by characterizing each droplet that passes through the probe volume and building up accurate ensemble statistics. The probe volume is formed by two (or four) intersecting laser beams, which provide a non-intrusive, high-spatial-resolution measurement point. In order to characterize a spray pattern, the measurement point, or more often the nozzle, is traversed to various locations within the spray pattern and many points are characterized through the spray pattern. This information is then combined to represent the drop size (or velocity or volume flux) distribution throughout the spray pattern. Further analysis allows combination of the information from the many individual data points to provide volume flux and area weighted average spray pattern statistics (ref: Bade_ILASS2013.pdf).
While the methodology is nearly identical, there are various commercial instruments available, such as the Phase Doppler Interferometer (PDI) and the Phase Doppler Particle Analyzer (PDPA). Spraying Systems Co. primarily uses the following instruments: