| As one of the important analytical methods in chemical analysis,titrimetric analysis has the advantages of rapidity,simplicity and high accuracy,and is widely used in industry,environment,agriculture and medicine.As the mainstream titration technique,manual titration has the defects of high subjective error,tedious operation and high work intensity,which affect the accuracy and efficiency of titration analysis.Based on the current situation that the titration analysis process is not automated enough,an automatic colorimetric titration system based on color sensors is developed in this project.The system uses a color sensor as the core component for detection and a peristaltic pump liquid supply device to automate the titration process.The system is suitable for titration analysis with colorimetric phenomenon and can effectively improve the accuracy and efficiency of titration analysis,and has a strong industrialization background.The main work of the project is as follows:1.In this paper,the overall scheme of the automatic titration system is proposed by comparing and analyzing the existing titration analysis techniques and titration devices.The scheme uses color recognition technology as the detection principle for titration endpoint determination,combines with CIE standard chromatography system for realtime detection of the color amount of the reaction solution during titration,and at the same time realizes digital representation of the color change of the solution during titration based on the relevant color difference calculation method to determine the endpoint of titration with quantitative indexes.Finally,the composition and working mode of each sub-module in the system are determined.2.Design and construction of the system hardware device.The whole system hardware device can be divided into color acquisition unit,automatic titration unit,human-machine interaction unit and main controller unit according to the functions.All the non-standard parts and related driving circuits are designed according to the functional requirements to improve the working stability of the system,while all the standard parts are selected,and finally the hardware device of the titration system is built.The detection system adopts color sensor AS7261 as the detection core,microcontroller STM32F103ZET6 as the control center and peristaltic pump as the titration feeding device to realize the automation of titration analysis process,combined with serial touch screen to provide friendly human-computer interaction for titration analysis.3.The software program of the automatic colorimetric titration system was developed and designed.The software program was firstly ported to μC/OS-Ⅱ real-time operating system,and then designed for each functional task to be scheduled and managed by μC/OS-Ⅱ to ensure the stable operation of the system.At the same time,a friendly human-computer interface was developed to realize the functions of process control in titration and analysis and judgment of titration endpoint.4.Experimental verification of the practicality of the system was carried out.Firstly,the titration accuracy of the peristaltic pump feeding device was calibrated,and the results showed that the peristaltic pump has high accuracy and stability.Then the performance of the automatic colorimetric titration system was evaluated using standard hydrochloric acid and sodium hydroxide reagents.The test procedure was performed by titrating five different concentrations of hydrochloric acid solutions with sodium hydroxide solution,and each set of tests was repeated five times.The results showed that the relative standard deviation of the titration system was about 0.5%,indicating that the system has good stability and the detection error of the system does not exceed 2%,which meets the accuracy requirements of the national standard GB/T11064.12-2013 for the acid-base titration method.After a long period of online testing,the developed automatic titration instrument can basically meet the needs of titration analysis in the laboratory. |
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