| The electrochemical analysis is essentially the study based on the response current generated during a chemical reaction,in which the chemical reaction is characterized by measuring the electrical parameters.Electrochemical analysis methods can be categorized as cyclic voltammetry,chronoamperometry,differential pulse voltammetry,etc.Electrochemical analysis methods need to be implemented in the test system,and the commonly used electrochemical test system can be divided into the two-electrode system and the three-electrode system.Compared with the two-electrode system,the threeelectrode system improves the situation of electrode potential shift,in which the constant potential control is the key part.The constant potential meter is the interface of the electrochemical three-electrode system.Generally,the electrochemical sensor is used as the sensing front-end of the constant potential meter with the constant potential control circuit,microprocessor unit,signal processing unit,etc.to form the constant potential system.The different external excitation signal is applied to the constant potential meter according to the electrochemical analysis method.When the excitation signal is applied to the three-electrode system,the response signal of the electrochemical reaction can be generated and measured.Then the signal processing unit in the potentiostat analyzes and processes the corresponding response signal to derive the electrochemical information.The emergence of the potentiostat has greatly broadened the means of electrochemical analysis and has enabled the field of electrochemical analysis to develop in the direction of integration and portability.Conventional potentiostats are complex,expensive,and in large size,therefore,portable potentiostats have emerged to reduce the size of the system and make the testing easier,in recent years.However,these portable potentiostats sacrifice the system resolution of the single method to accommodate multiple electrochemical analysis methods.To address these shortcomings,a high-resolution portable potentiostat system is designed in this thesis.The system adopts the chronoamperometry method,which is more suitable for immediate detection and quantitative analysis,and adopts the screen-printed three-electrode as the sensing front-end with the advantages of low sample consumption and immediate detection.In terms of hardware design,the peripheral circuit is composed of a power supply unit,a constant potential control unit,an I/V conversion unit,and an analog-to-digital conversion unit.In addition,the chip selection,software simulation,schematic design,and PCB design of the peripheral circuit are completed.Sigma-Delta type analog-to-digital conversion chip AD7787 peripheral circuit and PCB layout rules are introduced,and a multimeter,oscilloscope,logic analyzer,and other instruments are used to verify the function of the hardware unit.In terms of software design,the ARM-Linux platform with microcontroller(MCU)is used to drive the peripheral circuits,and the control driver of the constant potential system and the application program based on the QT platform are accomplished,focusing on the application layer logic of the analog-to-digital converter(ADC)driver and the graphical user interface(GUI)based on the IIO framework.The designed and completed constant potential system does not require PC power supply or interactive data,and users can set parameters and read data by touching the screen.Finally,the designed and fabricated constant potential system was tested for the concentration of glutamate solution.The results show that the constant potential system consumes a small amount of sample to be measured,and only a few drops of solution are needed to complete the test,and the error of the test results is within the allowable range with the maximum resolution of n A level.The constant potential system designed and fabricated in this study is small and portable,which can meet the needs of portable testing scenarios. |
PDF Full Text Request