Static spray deposition distribution characteristics of PWM-based intermittently spraying system

Owing to its intermittently spraying characteristics, spray deposition distribution uniformity of PWM-based variable rate application system is hard to control. A PWM-based variable rate application testing system was constructed by integration of a modified commercial boom sprayer and an IPC-based measurement and control system to study its static deposition distribution characteristics. The sprayer consisted of a fluid tank, a filter, a diaphragm pump, a proportional relief valve, 12 high speed on-off solenoid valves, 12 TR80-05 hollow-cone nozzles and various pipelines, mounted on a tractor, and was driven by the tractor via its power take-off shaft. The IPC-based measurement and control system was composed of a pressure sensor, 4 flow sensors, a signal conditioning module, an IPC, an analog input data acquisition card、a PWM signal output card、an analog output card, and 2 driving modules. Real-time monitoring of subgroup flow and boom pressure, feedback stable control of average boom pressure, setting of the average boom pressure, and setting of frequency and duty cycle of the PWM signal were performed by the measurement and control software which was developed with Labview. Droplets were collected with a matrix-styled droplet collection device, it had a horizontal collection dimention of 1000 mm×1000 mm and was divided evenly into 20×20 grids. Putting a paper cup in each grid, weighting the cups before and after each spraying test, droplet deposition of each grid could be deduced, and two-dimentional deposition distribution was obtained. Static deposition distributions of the PWM controlled nozzle were tested under various spray conditions of different spray pressures, different frequencies and duty cycles of PWM signal with the tractor holding still and the tested nozzle 0.5 m distance above the droplet collection area. And nonlinear regression analyses were performed on static deposition distribution specimens acquired under spray conditions of 0.3MPa spray pressures, 2Hz PWM signal frequency and different PWM signal duty cycles to construct their static deposition distribution models on dimension of droplet collection grid unit. Test and analysis results show that static deposition distribution models of the TR80-05 hollow-cone nozzles have a centrosymmetric shape of circular ring and accords with the two-dimensional dual normal distribution, droplet deposition and radius of the deposition circular ring increase with the increasing of spray pressure, droplet deposition is approximately proportional to the duty cycle of PWM signal, the duty cycle of PWM signal has less effect on radius of the deposition circular ring, and the frequency of PWM signal has less effect on the static deposition distribution.