Calibration of mass flux measurements of a phase-doppler interferometer
 
A phase-doppler interferometer (PDI) is a laser-device that can simultaneously measure size and velocity for transparent liquid drops. By summing the mass and velocity of each drop and dividing by the probe area, the mass flux of the liquid phase may be calculated. There are numerous challenges in making PDI measurements, mainly related to the effects of a Gaussian profile in the laser beam cross section, so that the light intensity is highest at the center of the probe volume and lower at the edges, with the result that large drops are detected over a wider effective area than small drops. PDI measurements are sensitive to equipment parameters, including the voltage gain on the photo-multiplier tube (PMT) detector. The mass flux in particular is sensitive to the voltage, more so than the mean drop size. The calibration of the PDI voltage for use in mass flux measurements of agricultural sprays is discussed.