An electrostatic cloud droplet sizing device (electrostatic disdrometer) originally developed by Keily and Millen has been tested, modified extensively, and calibrated in our laboratory. The investigations have shown that soon after entry into the probe orifice, the incoming droplet is broken into many fragments. These impact and splash on an electrode raised to a 510 V potential. Measured pulses for a given droplet size give a reproducible calibration curve.
Airborne tests of the probe have shown it to operate reliably with minimal maintenance. Comparisons were made between values of the liquid water content measured by the electrostatic disdrometer and by the Johnson-Williams hot-wire, liquid-water-content meter and between the droplet size distributions measured by the disdrometer and by impaction slide replicas. The comparisons were satisfactory within the limits of instrument measuring and sampling errors and actual variations in the droplets spectra resulting from the separation of the instruments on the aircraft during the tests.