Research And Development Of On - Line Detection System For Multi - Channel Nutrient Solution

Since entering the21st century, with the growing population base, increasing shortage of water resources, environmental pollution and worsening food security situation is increasingly grim, continued reduction of arable land, reduce rural labor availability and other issues increasingly severe, soilless culture technology which has advantage of high water and nutrient utilization rate、occupies less space has been widespread concerned、Hydroponics is an important environment control method and it belong to soilless cultivation technology, nutrient solution offers a variety of nutrients which normal growth and development of plant is needed, and the concentration and the amount of ions in the nutrient solution is the key to ensure plant’s healthy growth.There are two ion concentration detection methods of nutrient solution, one is based on EC and pH online detection, another is laboratory analysis, but all of these two kinds of method have disadvantages. This system uses multi-component ion concentration of nutrient solution line detection method to detect the ion concentration, by this way system can comprehensive analyze the elements concentration changing during the process of plant growth, and prevent inaccuracy by using the method which only based on the EC and pH value. This paper study and design a multi-channel online detection system of nutrient solution, the system can simultaneously detect the concentration of nitrate ion, calcium ion, potassium ion, pH and temperature of the liquid. To improve the defects of the existing system, this system adding the function of sensor calibration and temperature compensation, by this way the measurement data can be detected more accurate.The main research content is as follows:(1)Based on STM32F103ZET6microprocessors and Keil μVision4integrated development environment, using modular programming method, and use STM32firmware library complete hardware and software design and development work of nutrient solution online multi-channel detection system, achieved Real-time ion concentration information display solution, data storage, data transfer, parameter setting work, the system user-friendly, flexible and easy to operate, stable and reliable.(2) Due to asynchronism absorption of nutrient solution components in the process of plant growth, ion current detection device can only to test the single ion concentration, for a variety of complicated problems when ion detection, four specific ion concentration Ca2+, K+, NO3-,pH be detected in this multi-channel real-time online detection system, and based on ion-selective electrode’s characteristics of high resistance, conditioning circuit designed for ion selective electrode impedance matching and filtering output signals to achieve a real-time detection of changes in the components of the nutrient solution.(3) According to drift characteristics of ion-selective electrodes, the detection system provides a function of ion selective electrode calibration, can be a good solution to the problem of drift when the ion-selective electrodes measure the ion concentration, and can improve the ion-selective electrode accurate of detection system, calibration related characteristics stored in the EEPROM by system and that information will used in the system to detect.(4) Based on existing detection system lack of temperature compensation function when using ion-selective electrode, this system using DS18B20digital temperature sensor to measure the temperature of the liquid nutrient solution by studying the principles of ion-selective electrodes, elements concentration of nutrient solution measured by the liquid temperature and corresponding calibration data of calibration solution stored in the EEPROM.(5) After completed the multi-channel nutrient solution online detection system, also research conducted laboratory tests test, for a single ion concentration were measured in the first place, measurement of experimental data show that the system measuring accuracy can reach more than95%, then the multiple ion measurement was tested at the same time, through the four types of ion concentration on the unknown nutrient solution concentration measurement, the accuracy of the measurement results show that high repeatability of the system, verify the performance of the system. Two parts to test the reliability of the measurement system was explained in further steps.