基于电容特性的植物叶片含水率无损检测仪

Non-destructive Moisture Detector for Plant Leaves Based on Capacitance

为实现植物叶片含水率的无损和准确检测,利用圆形平行板电容传感器检测植物叶片电容,利用直径为12.7 mm的圆形FSR402型压力传感器测量平行极板对植物叶片的压力,以MSP430型单片机为微控制器,设计了一种基于植物叶片电容检测其含水率的仪器。以玉米叶片为对象,研究了玉米叶片含水率和极板对叶片的压力对电容的影响规律,选取了极板对玉米叶片的最佳压力,建立了最佳压力下玉米叶片的电容与含水率之间的关系模型,并对模型的可靠性进行了检验。结果表明,玉米叶片的电容随含水率和极板对叶片压力的增大而增大,检测玉米叶片电容的最佳压力为4 N。玉米叶片湿基含水率为55%～80%时,所设计检测仪的含水率绝对测量误差为-1.2%～1.7%;在晶振频率为8 MHz下检测含水率的响应时间小于3 s。

To realize precise and non-destructive determination on moisture content of plant leaves,a moisture detector based on leaf capacitance was designed.Circular parallel plate capacitor was used to detect capacitance values of plant leaves,FSR402 pressure sensor was used to detect pressure on plant leaves given by circular parallel plates,and MSP430 single-chip microcomputer was used as microcontroller.Maize leaves were used as samples to study the influence of moisture content and pressure on obtained capacitance values,and the best pressure for maize leaves＇ capacitance determination was obtained.The model describing the relationship between capacitance and moisture content of maize leaves at the best pressure was established and verified.The results showed that the capacitance values of maize leaves increased with moisture content and pressure.The best pressure for obtaining capacitance values of maize leaves was 4 N.The running test indicated that the absolute measurement error of the designed detector for moisture content of maize leaves was-1.2% ～ 1.7% in wet basis when the moisture content was between 55% and 80%,and the response time was within 3 s at oscillation frequency of 8 MHz.