Design And Experiment Of The On-line Detection Device Of Capacitor Liquid Concentration

As the problem of water and fertilizer resources excessive utilization becomes worse and worse,fertigation system with advantages of water and fertilizer saving section received extensive attention.Fat liquid concentration detection is a key link in the process of fertigation system adjusting the ratio of water and fertilizer.The liquid fertilizer concentration detection with problem such as low measuring accuracy,unable to real-time online detection,based on above insufficient,the paper develop a on-line capacitive liquid fertilizer concentration detection device.The main research work is as follows:?1?Design a concentric cylindrical ring capacitive sensorsBased on the dielectric constant method,using of fat liquid dielectric property,design a concentric cylindrical ring capacitive sensor and its control circuit that is a kind of easy to install in main pipe of fertigation system.?2?On the basis of performance test for capacitive sensor excited by different frequency signal,determines the optimal excitation signal frequency and calibrates the frequency of the sensor.within the concentration scope of 1×10^-3?8×101-mol/L using of five kinds of water soluble fertilizer such as calcium super phosphate,potassium sulfate diammonium phosphate and potassium nitrate mixed with deionized water to configure a series of liquid fertilizer.the characteristics of capacitive sensor,output voltage relation with fat liquid concentration,temperature variation and stability were tested by ten kinds of frequency signal under range of 1?10 MHz.Test results show that:?1?sensors consume current increases with the frequency increasing Under the specific operating voltage;?2?under any frequency,sensor output voltage is negatively related to the liquid fertilizer concentration and R2>0.96,sensor temperature variation rate below 1.53%under any frequency;?3?the best stability of the sensor output is 4 MHz under 5.0 V working voltage.Considering actual engineering of fertilizer solution concentration change fast and fertilization time long,need better stability,low power consumption so choose 4 MHz as fixed frequency of the sensor and tests have been carried out to calibrate and verify its performance and the result show that the sensor output voltage is negatively related to the concentration of liquid fertilizer and R2>0.987;the maximum measure error of sensors is 9.8%,with better accurate performance.?3?liquid fertilizer concentration on-line detection device is developed and its performance was tested.Based on the core of capacitive sensor,a on-line detection device of liquid fertilizer concentration was developed.It be consisted by single chip microprocessor,select button and electronic display,etc,that could realize liquid fertilizer concentration on-line and display the result.within the concentration scope of 4×10-1?4×10^-3 mol/L,using of urea,calcium super phosphate,potassium sulfate,diammonium phosphate and potassium nitrate water soluble fertilizer with deionized water allocation series of liquid fertilizer detects the timeliness and accuracy of measurement and the result show that:the device detection time<0.1 s,timeliness is strong;the maximum error of measuring accuracy is 9.83%,the performance good.To sum up,the liquid fertilizer concentration on-line detection device can be installed in the main pipeline of fertigation system to do the real-time on-line detection with high measuring accuracy,good stability and can improve water resource utilization,save fertilizer and water,protect the environment,promote the development of precision agriculture.