基于频域法的便携式无线土壤水分测量装置设计与试验

针对农田土壤水分测量的实际需要,研制了一种便携式无线土壤水分测量装置。该装置结构一体化设计采用"T"型结构,将土壤水分传感器和信息采集与发送单元融合,可在0~300 mm的不同深度下测量土壤水分,并采用蓝牙传输技术,将测量数据实时发送给Android手机,手机可通过App软件对数据进行分析处理,实现了农田数据的大容量存储和智能化处理。在实验室环境下,使用砂土和壤土2种土样对测量装置进行了标定试验,土壤容积含水率与传感器输出电压服从二次曲线关系,决定系数均达到0.99以上;将测量装置与波兰Easy Test TDR土壤测试仪进行对比试验,二者测量结果呈线性相关关系,决定系数为0.987。试验结果表明该装置可准确测量土壤水分含量。

Design and experiment of portable wireless soil moisture measuring device based on frequency-domain method

Abstract: At present, soil moisture content is mainly monitored by wireless sensor networks and determined by portable soil moisture sensors. Generally, the sensor needs to be embedded into the specified depth of the soil, which obviously disturbs soil. The construction is difficult, and the cost of the equipment input and maintenance is high. When using the soil moisture measuring device which adopts split design, the instrument and sensor probe need to be connected by wire. For a large number of field measurements, it is inconvenient. According to the needs of soil moisture measurement, a portable wireless soil moisture measurement device was developed. The portable wireless soil moisture measuring device mainly consists of 3 parts: PVC (polyvinyl chloride) handle, support rod and soil moisture sensor. The integrated design of device structure adopts "T" structure. The soil moisture sensing unit of the measuring device, the information collecting and receiving unit and the battery unit are integrated into the handle. The power switch and the power charging interfaces are respectively arranged at both ends of the handle. Soil moisture can be measured at different depths of 0-300 mm. The soil moisture sensor and the information collection and transmission unit are combined to reduce the volume and weight of the device, which makes it easier to operate in the field. The handle adopts a closed structure to realize water-proof and dust-proof performance. Acquisition and wireless transmission system consists of soil moisture sensor, information collection and transmission unit and mobile phone with Android system. Soil moisture sensor uses frequency domain method to measure soil water content, and the soil moisture content information is sent to the collection and transmission unit in the form of analog voltage signal. The information collection and transmission unit is composed of MSP430F149 microcontroller, GPS (global positioning system) module, FLASH memory and Bluetooth module. This unit transmits the soil moisture content of soil moisture sensor to the mobile phone with Android system through the Bluetooth transmission mode and stores the measurement information by App (application). By the App, mobile phone analyzes the data processing, controls the test device and stores data, realizing the large capacity storage and intelligent processing of farmland data. In the laboratory environment, in order to obtain the function relationship between the output voltage of the sensor and the soil volumetric water content, the sand and loam were used to calibrate the measuring device. The relationship between soil moisture content and sensor output voltage obeyed the quadratic curve relationship, and the correlation coefficients were above 0.99. However, because of the different texture of soil samples in the 2 kinds of soil, the correlation coefficients were different. Therefore, in order to improve the measurement accuracy of soil moisture sensor, the soil texture should be calibrated before used. The measurement device was compared with the Poland Easy Test TDR (time-domain reflectometry) soil tester. Fifteen groups of soil samples with different moisture content were randomly taken and measured by the Poland Easy Test TDR soil tester and the portable wireless soil moisture measuring device respectively. The measurement results showed a linear correlation, and the correlation coefficient was 0.987, which indicated that the measuring device can accurately measure the soil moisture content.