Response time of a direct injection type-variable-rate sprayer

Abstract

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

Keywords: direct -injection system; variable-rate sprayer; system response time