基于交流阻抗法的土壤湿度测量

Measuring Soil Moisture Based on Alternating Current Impedance Method

采用交流阻抗法快速测量土壤的湿度.将双探针传感器一端插入土中,作为阻抗器件,另一端与NE555芯片相连,组成电阻频率转换电路,使加载在被测土壤上的直流电变为交变电流,同时将土壤的交变阻抗转换成频率信号,不需要模数转换,就可以通过单片机测得频率值.通过频率与土壤湿度间的线性关系,获得土壤湿度值.交流阻抗法有效克服了在直流电作用下带来的土壤电极极化现象,在快速测量的同时保证了测量精度.实验结果表明该方法能有效测量0%～20%的土壤湿度范围.

The soil moisture was quickly measured by the alternating current impedance method. The doubleprobe sensor was inserted into the earth at one end,which was used as an impedance device,and the other endwas connected with the NE555 chip,which formed the resistance frequency conversion circuit. The circuit madethe direct current loaded on the soil changing into the alternating current,and converted the alternating imped-ance of the soil into the frequency signals;meanwhile,the frequency values were measured by a single chip,without analog to digital conversion. Finally,the soil moisture values were obtained according to the linear rela-tionship between the frequency and soil moisture. The alternating current impedance method overcomes effec-tively the polarization phenomenon of soil electrode under the action of direct current,with high precision andquick speed. Experimental results show that this method can measure the soil moisture in ranges of 0%-20%effectively.