基于脉宽调制的文丘里变量施肥装置设计与试验

为利用文丘里施肥器实现变量施肥,基于脉宽调制(pulse width modulation,PWM)技术设计了一种水肥一体化变量施肥装置,它主要由压力变送器、文丘里施肥器、脉冲电磁阀及控制器组成。通过改变PWM的占空比对脉冲电磁阀进行控制以改变文丘里施肥器进出口压力差,从而改变文丘里施肥器的吸肥量。以压力变送器检测管道入口压力,通过试验标定的方法将入口压力转化为相应的流量信息,从而获得施肥量和施肥质量分数。在多个入口压力水平下进行了试验,试验结果表明:电磁阀PWM控制的最佳频率为6 Hz;入口流量与入口压力呈线性正相关关系,决定系数为0.9936;施肥装置的最佳入口压力范围为0.15～0.25 MPa,在此压力范围内改变PWM的占空比对电磁阀进行控制,可实现施肥质量分数在1.25%～9.13%范围内可调。

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.