An approach to developing variable-rate sprayer technologies is to install electronic control systems on conventional\nsprayers. This study introduces a direct injection type electronic solution concentration control system. This control system\nwas installed on a field sprayer, and then a map-based variable-rate sprayer was developed. The control system consisted of a\nchemical tank, a chemical metering pump, the metering pump�s driver, the metering pump�s speed sensor, the implement�s\ntravelling speed sensor, an Electronic Control Unit (ECU), a GPS receiver and a mixing unit. The metering pump discharge\nwas measured at different carrier liquid (water) working pressures (3, 4 and 5 bar) and different chemical metering pump shaft\nspeed (100, 200, 300 and 400 r/min, i.e. pump�s working range). Data analysis showed that the effect of metering pump speed,\nsprayer working pressure and their interaction was significant (P<0.001) on the metering pump�s discharge. Metering pump�s\ndischarge function and the independent variables of pump speed and working pressure were calculated. In order to determine\nthe system response time, an electromotor replaced on the right hand front wheel of the tractor (the implement�s traveling speed\nsensor location), thus simulating the implement�s movement. An Electrical Conductivity (EC) sensor was mounted on\nrightmost nozzle of the boom. The chemical tank was filled with thick brine. The system response time was measured at\ndifferent working pressures (3, 4 and 5 bar), travelling speeds (3, 6 and 9 km h-1) and spraying concentration change rates (2, 3\nand 4 L ha-1). The working pressure was the only variable with a significant effect on the response time at the 1% level. The\nmean of response times were 25.8, 22.8 and 17.9 s at 3, 4 and 5 bar working pressures, respectively. The look-ahead firmware\nof the system was designed using the determined response time.
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