Measurement variations in reference sprays for nozzle classification

Variations in spray droplet measurements were identified for reference nozz les sewing as category thresholds defined for the standardized classificati on of agricultural spray nozzles. Spraying Systems, Delavan, and Lurmark ma nufactured brands of reference nozzles produced mean volume median diameter s (D-nu 0.5) that varied from 0.5 to 34 mu m within a given nozzle size, as measured with a laser diffraction instrument. Similarly, mean D-nu 0.1 and D-nu 0.9 values differed from 0.1 to 14 mu m and from 0.9 to 74.2 mu m, re spectively. Coefficients of variation (CV) in D-nu 0.1, D-nu 0.5, or D-nu 0 .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 pro be and a phase Doppler instrument. Relative droplet size differences betwee n nozzle brands were noted when using different types of laser instruments compared with number density weighted values. Similarly, droplet size diffe rences were observed between instruments compared with number flux weighted values. Results indicate that dedicated reference nozzle sets may be prefe rred to increase the overall uniformity of classification thresholds; any o f the tested brands of nozzles would be suitable; and laser instrument diff erences may contribute to relative shifts among thresholds for nozzle class ification, thereby reducing the precision of uniform nozzle classification.