Research On Key Technologies Of Micro-reagent Water Quality Detection Based On Flow Control Technology

The problem of water pollution has seriously affected people’s living standards.The primary task of solving this problem essentially is to monitor water environment through advanced technology.At present,the main detection methods of water quality are spectral method,electrochemical method and chemical reagent method,spectral analysis is also limited by light source and high instrument cost;the electrochemical method has the advantages of poor selectivity,low service life and high maintenance cost;chemical reagent method has the advantages of high reagent loss,high labor cost and easy to produce secondary pollution,Ultraviolet spectrophotometry has the advantages of high detection accuracy,small amount of reagent,short detection time and low cost.Therefore,it is of great practical significance to study a kind of water quality detection equipment based on flow control technology and ultraviolet spectrophotometry.In this paper,a new type of dual-channel injection pump is designed to solve the problems of low detection accuracy and poor stability of the injection pump,which is the key component of the sequential injection water quality monitor,and the key technologies such as closed-loop control of injection system and removal of bubble interference are studied.1.Aiming at the problems existing in the structure of the existing injection system,we proposed a new design method of injection pump with a more compact structure,that is,a hollow shaft potentiometer was set at the ball screw of the motor,and the potentiometer was used as position feedback device.This method can feedback the piston stroke of injection pump accurately,so as to improve the injection precision and sealing performance of injection pump.2.In order to solve the problem of low detection accuracy of sequential injection water quality monitoring equipment,a closed loop control system is designed.In this paper,two-phase hybrid stepping motor is used as the power source of injection pump.According to the control requirements of the motor,we designed the motor fuzzy PID control algorithm to realize the closed-loop control of the two-phase hybrid stepping motor.Meanwhile,we established the motor fuzzy PID control model in MATLAB/Simulink module,and compare the fuzzy PID control with the ordinary PID control,the results show that the fuzzy PID control has obvious advantages.Besides,aiming at the problems of large measurement errors caused by bubbles in the pipeline of the existing monitoring instrument in the measurement process,the multi-channel switch valve island system is introduced in this paper.The injection pump is combined with the valve island system,and the sequential injection technology is used to write the program to control its running state,so as to reduce the measurement error of monitoring instrument.3.The design of the injection system is completed.It mainly includes the design of the overall scheme and structure of the injection pump and the establishment of the multi-channel valve island system.Simultaneously,taking total phosphorus,ammonia nitrogen and permanganate index as test parameters,the micro-reagent sequential injection platform was designed,and the feasibility experiment was carried out,The software and hardware of the system and the design of system flow control are completed.The serial communication protocol between the valve island of the injection pump and the main control board is completed.4.We compare the measured values of the water quality detection system with those of the national standard method through the water quality testing performance experiment,proving the trustworthiness of the experimental results.The relative standard deviation（RSD≤2.55%）of each water quality parameter is low,that is,the repeatability is high.The goodness of fit（R~2≥0.9898）is high,that is,the linearity is good.Both reliability and accuracy meet the technical requirements of water quality on-line monitoring equipment.Therefore,the monitoring scheme in this paper has application value.In other words,we put forward a new design idea for online monitoring instrument research.