Research On The New Multi-index Measurement Technology Of Surface Water Quality

pH and conductivity are important indexes for surface water quality, the mostwidely used measurement methods in home and abroad for this two indexes are pHglass electrode measurement and conductivity electrode measurement. However, suchmeasurement methods still have many problems when they are used in the practicalapplications. Such as the glass electrodes are easily broken, the electrodes should befully soaked before using, the accuracy of measurement is easily being influenced bythe temperature and the solution which is under test; The ability of anti-pollution andcorrosion resistant of conductivity electrodes are poor, the effects of electrodepolarization affect the accuracy of measurement.In order to overcome these problems, this paper designed a three-electrode sensor,which used boron-doped diamond electrodes as working electrode and counterelectrode. Boron-doped diamond electrode is a new kind of electrochemical electrodes,the electrode uses boron-doped diamond thin film of sp3bond structure as theelectrode material, so that the electrode has excellent electrical conductivity andelectrochemical properties, such as wide potential window, low background current,strong physical and chemical stability and poor adsorbability. Based on thethree-electrode electrochemical system, this paper used Chronopotentionmetry andaquare-wave current methods to achieve the simultaneous measurement of pH andconductivity. Overcomed the effects of alkali cations in the solution to the acuuracy ofpH, and the effects of electrode polarization to the accuracy of measurement. Thispaper also designed a turbidity sensor which can measurement scattered light andtransmission light in the same time. Added with the measurement of temperature, thissystem achieved the measurement of multi-index. This paper designed the systems of hardware and sorfware, the hardware systemis based on C8051F120, it includes constant current circuit, signal acquisition, A/Dconversion circuit, RS232circuit and so on; the software system is based on MCGSembedded configuration software, this system used to control external devices,process the data and display the results.This paper includes three kinds of experiment(pH, conductivity, turbidity), boththe calibration curves of pH and conductivity experiments showed that themeasurement methods of Chronopotentionmetry and aquare-wave current are feasiblefor pH and conductivity. The results of the turbidity experiment ensured themeasurement range of the scattered light method and transmission light method.The design of three-electrode sensor made up for the defects of traditionalmeasurement techniques, promoted the developments of measurement methods ofsurface water’s pH and conductivity, improved the stability of multi-index instrumentand reduced the cost of the products. The measurement combined scattered light andtransmission light improved the accuracy of turbidity measurement.The main innovation of this paper is as follows:（1） The first time to use BDD electrodes for the simultaneous measurementsof surface water’s pH and conductivity;（2） The use of a three-electrode electrochemical system with BDD electrode,designed and made a sensor that can measure pH and conductivity in thesame time.