MODIFICATION AND TESTING OF A COMMERCIAL SPRAYER WITH PWM SOLENOIDS FOR PRECISION SPRAYING

A commercial sprayer was modified for variable–rate control of 25 individual nozzles on an 18.3–m (60–ft) sprayer boom. The variable–rate control system consisted of pulse–width modulation (PWM) solenoids, a pressure controller, and a nozzle control system interfaced to a computer. Map–based application software was developed. The application software is compatible with remote–sensing–based nitrogen prescriptions and is capable of providing highly accurate application rate control. Tests were conducted to evaluate the volumetric application accuracy of the variable–rate sprayer. The flow rate changes due to inaccuracy of the pressure controller ranged from 0.5 to 2.2% in our tests. The valve–to–valve differences in flow rate response to PWM signals were the primary causes of the volumetric inaccuracy. When a single flow rate calibration curve was used, flow rate control errors for valves ranged from
15 to 12%.