Research Of Electric Field Coupling Induction Type Conductivity Detecting System

Electrical conductivity as an important measure of water quality,its measurement technology is an important field of engineering technology research,the conductivity sensor is widely used in human production and life,territory like environmental testing,wastewater treatment,industrial process control.In order to eliminate or improve the problems that the commonly used electrode type conductivity sensor has electrode corrosion,polarization effect and great temperature influence on its measurement precision,and further to achieve the purpose of measuring the electrical conductivity without metal conductor parts directly exposed to the electrolyte solution.An inductive conductivity detecting system is designed based on the electromagnetic energy transfer mechanism adopting electric field coupling method,the sensor probe was designed and optimized,the signal conditioning circuit is studied and designed,and the experimental design and characteristic compensation of the test system are studied,the main work is as follows:(1)An inductive conductivity sensor probe is designed based on the electromagnetic energy transfer mechanism adopting electric field coupling method,the working principle and structure parameters of the sensor are given,and the theoretical relationship between the measured conductivity and the output voltage is derived;(2)The signal excitation and conditioning circuit of the direct digital frequency synthesizer(DDS)and AD637 effective value detection circuit are designed,digital signal processing(DSP)chip TMS320F2812 was the core,control DDS chip AD9852 to generate excitation signal,meanwhile,the measured output signals after signal conditioning was collected,input to the system through A/D conversion,and keyboard input and display output and other functions are extended,constitute a complete electrical conductivity detection system;(3)For the influence of temperature and nonlinear characteristic on conductivity measurement,the voltage-frequency response and conductivity-temperature-voltage characteristics of the sensor are tested,the test data are processed with the least square surface fitting method,thus the nonlinear characteristic and temperature effect of the sensor are compensated,and the measuring method and compensation algorithm are verified.The results show that the sensor reaches a certain measurement precision,and it has the advantages of simple structure,high sensitivity and good durability,achieve the desired design purpose,it can be widely used in the measurement of liquid conductivity in various industries.