Variable-Rate Spray System Dynamic Evaluation

A MidTech TASC 6300 variable-rate spray control system was interfaced with a John Deere 4700 spray tractor. The dynamic response of the system was examined by measuring the response time between when a control signal was initiated and when the solution at the nozzle stabilized at the resulting concentration. These measurements were evaluated with three injection dyes at two tractor speeds and three application rates. Three FD&C dyes were chosen to simulate three chemicals in the injection tanks. A total of 1176 samples of solution from the nozzles were collected and analyzed with a spectrophotometer. Their absorbance characteristics were used to determine the response time of the spray system under various testing conditions. The results showed that the overall average delay time of the system was 38.3 seconds, and the rise time was 65.9 seconds. The response time varied with speed, but the product of speed and response time remained almost constant. The system took longer to achieve steady-state when the application rate varied from high to low than when it varied from low to high.