| Water is the source of life,and it is vitally important to the survival and development of human beings.With the development of economy and the improvement of people’s living standard,people’s demand for water quality is higher and higher.Domestic water,industrial water,agricultural water and other industries have different requirements for water quality,so the detection of water quality is particularly important.Turbidity is an important parameter for water quality evaluation.It refers to the degree of obstruction caused by solution to light passing through,including the scattering of light by suspended substances in solution and the absorption of light by solute molecules.The turbidity of water is not only related to the content of suspended matter,but also to their size,shape and refractive index.The turbidity of water is mainly caused by sediment,bacteria,microorganism,suspended particles,colloidal organic matter and inorganic matter.These impurities will not only affect the quality of water,but also cause the spread of disease.Therefore,the detection of water turbidity is particularly important.According to the basic principle of turbidity detection and the analysis of turbidity detection methods,a water quality turbidity detection system with wide measuring range,high accuracy and good stability is designed in this paper by using transmission method,vertical scattering method and ratio method.The main contents of this paper are as follows:1.In the sensor design,a sensor with wide detection range and high accuracy is designed by using light-emitting diode,photodiode,lens and temperature sensor according to the selected turbidity detection method.2.In the hardware circuit design of the system,in order to restrain the interference from the source,improve the stability and reliability of the system,the design of light source driving circuit,I/V conversion circuit,signal amplification circuit and temperature detection circuit is completed;in order to collect,process and control the data,the design of STM32 minimum system circuit is completed with STM32F407 as the system core;in order to display and output the detection results,the design of LCD interface circuit and serial communication circuit is completed.3.In the system software design,in order to collect and process the data,the A/D conversion program and data processing program are designed;in order to improve the stability and accuracy of the detection system,the key chattering program and the digital filtering program are designed;in order to store and read the data,the data reading and writing program is designed;in order to display the detection results,The LCD display program is designed.4.In the experimental results and analysis,zero turbidity water and formaldehyde standard turbidity solution were prepared according to the experimental requirements,and data detection,performance index testing and influencing factors analysis were carried out according to the configured sample solution.Finally,according to the data analysis and performance index test,it is concluded that: in the range of 0-450 NTU,the linearity of vertical scattering method is good;in the range of450-650 NTU,the linearity of ratio normal method is good;in the range of 650-1000 NTU,the linearity of transmission method is good.The experimental results show that the system has wide measuring range,high accuracy and good stability. |
