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In order to achieve variable rate fertilization by
Venturi fertilizer applicator, a variable fertilizer applicator based on pulse
width modulation (PWM) technology has been developed which composed of pressure
sensor, Venturi fertilizer applicator, two pulse solenoid valves and
controller. By adjusting the duty factor of PWM technology, the tow pulse
solenoid valve is controlled to control the pressure difference between the
inlet and outlet of Venturi fertilizer applicator, 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
best frequency for controlling the solenoid valve using PWM 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 of
fertilizer applicator was in range of (0.15-0.25) MPa and the fertilizer
concentration can be adjusted within (1.25%-9.13%) by controlling the PWM duty
factor of solenoid valve. (Li Jianian et al., 2012).

In this article to achieve variable rate of
fertilization by Venturi fertilizer applicator, a variable fertilizer device
was designed based on PWM (Pulse Width Modulation) technology. An integrated
variable fertilization device for water and fertilizer, It was mainly composed
of pressure transmitter, Venturi fertilizer applicator, pulsed electromagnetic
valve and controller. By changing the duty factor of PWM, the pulse solenoid
valve is controlled to change the pressure difference between the inlet and outlet
of Venturi fertilizer applicator; so the absorption of venturi injector was
changed. The fertilizing concentration and fertilizing quantity can be
calculated according to inlet flow rate, and the flow rate was calibrated from
the pipe inlet pressure which measured by pressure transmitter through
experimental method. The experiment results showed: the optimum frequency of
PWM for controlling solenoid valve is 6Hz; the fertilizer concentration could
be adjusted from 0 to 10% by changing the PWM duty factor from 60% to 100%. (Li
Jianian et al., 2012).

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