Design Of Portable Measurment Instrument On Plant Leaves Moisture Content

Realizing rapid and non-destructive determination and utilization on moisture content ofplant are not only useful for research of plant physiology information, but also can adopt toprecision irrigation of plants, improving the use efficiency of irrigation water. The leaf is animportant organ for photosynthesis, respiration and transpiration of physiological processes,and make great significance to guarantee water metabolism balance of the plant. Leafmoisture content can reflect the plant water status and physiological information. However,the structure of existing detection instruments for plant leaves moisture content is complexand the price is relatively high. although the method of oven drying method is highlyprecisive, but detection cycle is so long, can’t achieve the leaf moisture content detectionrapidly and non-destructivly. So, it is particularly important to develop a moisture contentmeter with low price, convenient operating, and high precision. Analyzed and summaried theexisting non-destruction testing methods of moisture content of plant leaves, based oncapacitance detection method, a portable plant leaf moisture meter was designed with16-bitsingle-chip Msp430f149as control core. The main tasks and results of this paper are asfollows:(1) Maize leaves and soybean leaves were used as samples to study the influence ofmoisture content and pressure on obtained capacitance values, the best pressure for leaves’capacitance determination was obtained respectively. The model describing the relationshipbetween capacitance and moisture content of maize leaves at the best pressure wasestablished and verified separately. The best pressure for obtaining capacitance values ofmaize leaves was4N, and coefficient of the model describing the relationship betweencapacitance and moisture content of maize leaves was0.9359; The best pressure for soybeanleaves was3N, and the coefficient of the model was0.9161.(2) The hardware system of moisture content meter was designed. With a16bitsingle-chip MSP430as the control core, capacitance detection and processing module,pressure detection and processing module, single-chip control module, input and outputmodule, power module were designed, The system could show the moisture content of plantleaves calculated on the base of detecting capacitance and pressure.(3) The software system written in C language was developed based on IARsystem forthe moisture content meter. It includes system’s primary function, A/D conversion, liquid crystal display, keyboard identification and moisture content calculating, etc.(4) The hardware circuit board of the meter was designed and manufactured byAltium-Designer, and the detector was debugged overall.The capacitance detection error waswithin±5pF and the relative error is less than±3%;The maximum relative error of thepressure is2.04%.(5) The detection performance of the meter was verified by experiment with corn leavesand soybean leaves as test samples. The running test indicated that the absolute measurementerror of the designed detector for moisture content of maize leaves and soybean leaves wereboth within±2%at the moisture content from55%to80%, and the respond time was lessthan3s.