| The monitoring on water content in plants is very important to irrigate plants in time and accurately, and to increase crop yield. In agricultural producing process of our country, the watery situation in the plant is usually monitored indirectly by monitoring soil moisture. The indirect technique may result in unreasonable usage of water resources because of its hysteretic nature. But in some developed Countries, the water content in the plants has been monitored directly by some new techniques, thus the plants have been served with the fine quantity irrigation. The effects of saving water 35% and increasing crop yield 40% are achieved. China is a large agricultural nation where water resources are extremely scarce. The studies on non-destructive monitor technique for plant water content are important to fine quantity irrigation in farmlands, to save the fresh water resources, and to increase crop yield.It the recent decade, the technique to monitor the water content in the plants has been given large attention by Chinese investigators. So far, one effective technique suggested by Chinese investigators is to measure the thickness of plant leaves using a machinery sensor. The measuring accuracy of the sensor can achieve the 0.001mm magnitude. The technique dose have high precision, but still have the following disadvantages: Firstly, slow drifting is existed in sensor and metering equipment; Secondly, the error of the micrometer mechanical system return trip is also included in the observed value; Thirdly, the error in measuring the thickness of the plant leaves and the mechanical error may result in the accumulation of the error. In order to develop the technique to non-destructive monitor on the water content in the plants, and avoid previous disadvantages, a capacitive sensor and system to non-detective monitor plant moisture content is developed in the study. The main contents of the study are as follows:(1) Based on analyzing the operating principle of capacitive sensor and mechanism of plant moisture content distribution, the investigating scheme for changing medium capacitive sensor and measuring position on the water content of the plants leaves are determined. Based on comparing the properties of several different capacities, a plate capacity which can be easily used to grip and fix the plant leaf is chosen as a sensor capacity. (2) A changing medium capacitive sensor is developed to monitor the water content in the plants. In the circuit of the sensor, the adjustability of output signal and limiting frequency in filtration are considered, the usage of the sensor is therefore very convenient. Because the capacity sensor itself can not be affected by environment temperature, the problem of The sensor can monitor the plant moisture content directly, thus the problem of temperature drifting is existed for the sensor. The sensor can be used to monitor directly the water content in the plant, and the output signal can directly reflect the change of the water content, the problem of accumulating errors doesn't exist.(3) Based on the software Multisim 8, the reasonability of the electric circuit of the developed sensor is simulated. In the simulation, the properties of every part in the circuit is examined, analyzed and optimized. The little change of the water content is simulated by the change of sensor capacity. Base on the simulation, the relationship between the plant moisture content and the output signal of the sensor is obtained. The results indicate that the relationship is linear with great related coefficient, and the properties of the developed sensor are very well.(4) Based on theoretic analyzing the effects of environment temperature on the conductance of the plants and environment humidity on the electric signal of the sensor, a system to real-time monitor the plant water content is developed. In the system, the influence of environment temperature and humidity can be considered, and the consideration can improve the accuracy of the sensor. |
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