Data acquisition system for evaluating spatial accuracy of selective-type sprayers

The purpose of this research was to test and evaluate a data acquisition system (DAS) that could record a real-time discrete (on/off) event and geo-reference that event with a GPS coordinate. For this research, two selective-type sprayers were used as the site-specific input. The objectives of this experiment were to geo-reference the discrete on/off signal from these sprayers with GPS, generate an application map for the sprayer systems, and compare these application maps to known vegetative coverage.

To accomplish these goals the selective-type sprayers, Detectspray and Weedseeker, were mounted on a three-point hitch sprayer equipped with a 55- gallon tank and a PTO driven 6-roller pump. An interface composed of opto-isolators was designed to isolate the sprayer systems supply voltage from the DAS, and to convert the +12-Vdc analog valve supply voltage to a digital +5-Vdc signal for the DAS. A Trimble AgGPS 132 receiver with differential corrections provided the DGPS signal for these studies.

To field test the system two experiments were performed. The first field test was conducted with a known vegetation/soil pattern setup using dense 15-ft. wide soybean rows with 30 ft. of bare soil between. Two speeds, 2.5 and 5.8 mph, were used to evaluate the affects of speed on the system. In addition, travel direction was oriented at a 45° angle to the orientation of the rows to activate and record each individual nozzle. The second field test was conducted using random vegetation/soil patterns setup with random tillage and random vegetative growth. Two GPS Input frequencies, 1 and 2 Hz, were used to determine if the system could record both rates.

A volumetric evaluation was conducted to verify the recorded data from the DAS to the actual application from the sprayer systems. Artificial activation devices were used to turn the nozzles on and off. The DAS recorded a file while fluid was collected from the solenoid-activated nozzles. A percent of continuous flow was calculated for the nozzles and compared to the percent recorded by the DAS.

Application maps generated for the field tests for both sprayer units display spatial applications of the sprayer systems. These maps were compared to known vegetation maps, and proved to be accurate. The volumetric evaluation verified that values recorded by the DAS were related to the actual application from the sprayer systems. Therefore, the DAS proves to record and reference a real-time discrete site-specific event with a GPS coordinate.