Sistema a basso costo ed elevata affidabilità per la misura dell’ uniformità di distribuzione delle irroratrici

To verify the real increase of the distribution uniformity quality of the computerized control of the flow rate in normal but, above all, in critical operating conditions (i.e. spraying on slopes, end of the run, etc.) a "dual" boom sprayer was manufactured, by fitting on a single frame two complete spraying systems, being the first a traditional type (distribution proportional to the engine speed) and the second equipped with a micro-processor based system, able to dinamically control the flow rate. The dual sprayer was tested on slopes, adopting an innovative method by using a great number of samples having a high absorbent capacity will be placed on the ground, to define an experimental scheme based on a sort of grid of 5x5 m indicatively. The samples were wetted in various amount during the distribution trials. Furthermore, the marker was extracted from every paper sample: the correspondent water samples were coloured with an intensity proportional to the marker amount extracted from the paper samples. For the evaluation of the marker concentration, the use of a spectrophotometer seems normally to be the more suitable solution but, due to the very high cost of such instrument, the purpose was to define a simple alternative methodology, based on the use of a set including a LED and a photo diode: the first is emitting light in a very narrow frequency range; the second is very sensible, in that range, to the light intensity variation caused by the different concentration level of the marker into the solution. Such device was positively manufactured and tested, and the resulting signal was treated through a data acquisition card driven by a dedicated software, and the more suitable data were obtained. The described system highlighted: - a very high sensitivity, showing an excellent measuring precision up to a marker concentration of 5 ppm; - a good repeatability of the results (max tolerance ± 7 % for further measurements of the same sample); - an excellent discriminability (up to 1 ppm); - a very short sample analysis time (few seconds); a very low cost of the device, also compared to that of an "entry level" mass spectrophotometer.