A Study Of On-line PH And Electrical Conductivity Measurement System In Seawater Desalination

Our country is facing the serious water resources crisis. It is efficient to develop the seawater desalinization technology to solve the fresh water problem in coastal area. The pH and conductivity are very important parameters to weigh the water quality in the seawater desalination system. Therefore, it is very important to study online measurement technology about the pH and conductivity parameters in the seawater desalination.The measurement theory and the characteristic about the pH and conductivity were analyzed. According the special request of seawater desalination system, a high performance signal processing circuit about pH measurement which is based on potential method was designed. A conductivity measurement method based on frequency conversion driver resource was proposed. The system about online pH and conductivity measurement in seawater desalination was designed. The main research work of this paper is as follows:(1) PH measurement theory based on the potential method had been researched in this paper. The factors affected pH measurement had been analyzed. In view of the high internal resistance of pH electrode and external disturbance, the amplifier circuit was designed with high input impedance and capacity of resisting disturbance was designed. In view of the characteristic of pH electrode signal, the software filtering algorithm based on the mean value was designed to increase the accuracy of pH measurement and capacity of resisting disturbance.(2) The conductivity measurement theory had been researched in this paper. The factors influenced conductivity measurement had been analyzed. In view of capacity effect and polarization effect produced in the measuring process, a conductivity measurement method based on frequency conversion driver resource was proposed. The frequency of different conductivity scope was also provided. Therefore, the conductivity measuring error was reduced. The frequency conversion driver source circuit had been designed and the peak value acquisition algorithm of sine wave was also designed to ensure the acquisition precision of conductivity signal. In view of the influence of temperature, the temperature compensation method had been designed to increase the conductivity measuring accuracy.(3) The multi-thread application program used to acquaint, processe and display data was designed to ensure the man-machine interaction timely and the continuity of signal acquisition. The driver program about hardware circuit based on Linux system was completed. It could ensure that Linux system could quickly visit hardware equipment.(4) The online pH and the conductivity measurement system in seawater desalination was developed. The ultrasonic cleaning device was designed to realize the function of online examination and maintenance in the seawater desalination system.(5) In order to weigh above parameters, ultrasonic cleaning debugging experiment, online examination precision experiment and system stability experiment was designed separately. Ultrasonic cleaning experiment is used to check the online cleaning effect; online measurement precision experiment verifies the system accuracy; the system stability experiment checks the long-term running stability under the industry environment.This system has passed the debugging of laboratory and scene. The pH measuring accuracy was smaller than±0.1 and conductivity measuring accuracy was±2% in full scale.