MEASUREMENT VARIATIONS IN REFERENCE SPRAYS FOR NOZZLE CLASSIFICATION
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Variations in spray droplet measurements were identified for reference nozzles serving as category thresholds
defined for the standardized classification of agricultural spray nozzles. Spraying Systems, Delavan, and Lurmark
manufactured brands of reference nozzles produced mean volume median diameters (Dv0.5) that varied from 0.5 to 34 µm
within a given nozzle size, as measured with a laser diffraction instrument. Similarly, mean Dv0.1 and Dv0.9 values differed
from 0.1 to 14 µm and from 0.9 to 74.2 µm, respectively. Coefficients of variation (CV) in Dv0.1, Dv0.5, or Dv0.9 within a
nozzle brand and size ranged from 0.19 to 3.62% across the test. Two additional laser instruments that were tested
included an imaging probe and a phase Doppler instrument. Relative droplet size differences between nozzle brands were
noted when using different types of laser instruments compared with number density weighted values. Similarly, droplet
size differences were observed between instruments compared with number flux weighted values. Results indicate that
dedicated reference nozzle sets may be preferred to increase the overall uniformity of classification thresholds; any of the
tested brands of nozzles would be suitable; and laser instrument differences may contribute to relative shifts among
thresholds for nozzle classification, thereby reducing the precision of uniform nozzle classification.