Design and experiment of Venturi variable fertilizer apparatus based on pulse width modulation

In order to realize variable rate fertilization with Venturi Injector, a variable fertilizer apparatus based on PWM (pulse width modulation) technology has been developed, which consists of a pressure sensor, a venturi injector, two pulse solenoid valves and a controller. The apparatus is based on the Venturi effect with the ratio of flow in the main pipe to that in the venturi nozzle being controlled by the pressure difference. The pressure difference between inlet and outlet of Venturi Injector is controlled by controlling the pulse solenoid valve controlled using PWM technology with a duty factor, a function of the pressure difference. With the PWM duty factor changed, fertilizer concentrations can be changed. The fertilizing amount and fertilizing concentration were determined based on the inlet flow rate calibrated from the pipe inlet pressure. Experimental results showed that the optimum frequency of PWM for controlling the solenoid valve was 6 Hz and the inlet flow rate had a positive linear relationship with the inlet pressure and the correlation coefficient was 0.9936. The optimum inlet pressure range of the fertilizer apparatus was 0.15-0.25 MPa and the fertilizing concentration can be adjusted within 1.25%-9.13% by controlling the PWM duty factor of solenoid valve.