CAJ | 학술논문

研究土壤含水率的测定对于农作物生长，灌溉及农业自动化发展具有重要意义。该文针对传统含水率传感器电极输出信号谐波失真较大的问题，设计了一种差分信号控制的土壤含水率传感器。鉴于传感器电极输出的信号失真是由于土壤非线性因素引起的，该文利用集成时基计时器设计差分输入信号控制电路，减少输出信号的总谐波失真度。此外，建立相应的数学模型，得到土壤阻抗与信号周期变化关系。构建传感器硬件结构，通过微处理控制器测量信号周期得出土壤含水率变化数值。试验表明，传感器输出端的信号总谐波失真较传统结构减少12.56%。土壤质量含水率在5%~30%时，土壤含水率测试最大误差不超过4.89%，土壤阻抗测试误差不超过2%。
연구토양함수솔적측정대우농작물생장，관개급농업자동화발전구유중요의의。해문침대전통함수솔전감기전겁수출신호해파실진교대적문제，설계료일충차분신호공제적토양함수솔전감기。감우전감기전겁수출적신호실진시유우토양비선성인소인기적，해문이용집성시기계시기설계차분수입신호공제전로，감소수출신호적총해파실진도。차외，건립상응적수학모형，득도토양조항여신호주기변화관계。구건전감기경건결구，통과미처리공제기측량신호주기득출토양함수솔변화수치。시험표명，전감기수출단적신호총해파실진교전통결구감소12.56%。토양질량함수솔재5%~30%시，토양함수솔측시최대오차불초과4.89%，토양조항측시오차불초과2%。
Measurement of soil moisture is important for water management in crop cultivation, design of irrigation schedule and development of agricultural automation. Harmonic distortion of soil moisture sensor is high so that the measurement of soil moisture content by using those sensors has a large deviation. Therefore, a new design of soil moisture sensor based on differential signal was proposed in this study. The sensor consisted of six parts, which were circuit based on differential signal, correcting circuit, waveform generator, microcontroller unit, power conversion module and electrode module. Since the output signal of senor electrode had harmonic distortion due to the nonlinear factors of soil, a new circuit scheme was proposed using integrated time-based timer to design differential signal control circuit. The relationship between soil resistance and signal period was analyzed by mathematical models. The soil moisture could be obtained by constructing the hardware structure of sensor and measuring the signal period on microprogrammed control unit (MCU) controller in terms of the relationship. The two ends of input waveform in differential signal control circuit were with equal amplitude and phase difference of 180o. Thus these electrodes were almost equal to differential signal. Energy of even order harmonic distortion reduced, while odd order harmonic distortion energy increased at the same time. Moreover, considering the probability of mismatch to electric characteristic parameters, the variance ratio of period of signal in the output was less than the proposed circuit. To verify harmonic distortion of the proposed sensor, frequency spectrum was obtained by utilizing the software of electronic design automation for the proposed sensor with two ends of input-output and classical sensor with a single end of input-output. Total harmonic distortion of traditional circuit for a single end of input-output was 47.40% where the voltage amplitude of two-order harmonic and three-order harmonic was as high as 0.325 and 0.516V, respectively. In contrast, differential signal control circuit could be applied to improve harmonic distraction where the voltage amplitude of two-order harmonic was 0.097 V and that of three-order harmonic was 1.161 V, respectively. Experiment on the proposed sensor was organized as follows. Firstly, the sensor was calibrated by utilizing two types of soils including loam and sandy soil. Secondly, the sensor was evaluated in the soil samples with different soil moisture content. The result showed that the total harmonic distortion of this sensor of output signal was lower than traditional one. The maximum absolute error of soil moisture was less than 4.89% and the error of soil resistance was less than 2% when soil moisture was between 5% and 30%. The absolute error of soil resistance was less than 10% in the condition that soil moisture was in the interval of 30% and 47%. The study provides an effective method for design of soil moisture sensors.