Based On The Potentiometric Method Of Intelligent Online Ph Analyzer Design,

This article has briefly discussed the necessity and the evolution of pH analyzers, and also introduced the designing progress of the Intelligent Online pH Analyzer based on direct voltage method.In this article, solution's ionization and pH definition were first reviewed. The performance of electrochemical sensor adopted by this design was then studied and analyzed in detail with strict deduction, which provided theoretic foundation for subsequent analyzing. The succeeding work is to process data and to analyze disturbances, which is the most important part of this article. As pH glass electrodes have great inner resistance, and based on the analysis of impedance, a measuring amplifying loop with 10¹⁵O inputting resistance was chosen to acquire accurate voltage signal, while a 2.252k negative temperature coefficient (NTC) thermistor was adopted for temperature measuring. Under circumstance that all those performance standards were satisfied, 0.25mA constant power supply and amplifying loop would be the best choice temperature measuring with high precision. the function of two-point calibration of the temperature sensor is added to this design,which improves the precision of temperature measuring. Among all sorts of disturbance, temperature is the major affection to measuring pH value. In this article, designer selects proper measuring amplifier, obtains experimental data by testing water sample with various properties, and then acquires temperature compensating formulas for normal water, pure water and highly pure water. Besides, electromagnetic disturbance is efficiently reduced by adding a shield, also affections derived from flux and ground loop are removed by adding flux compensation and triple composite electrode with liquid ground. After summarizing all sections above, testing sample meter for a great deal of times and constantly modifying formulas to acquire results with much higher precision. In the digital processing module Low-powered, high-performanced microcontroller and peripheral chips are used in this design and system software has the ability to store and display historical data, to function intelligently with Chinese/English interface. By using touching screen with true color, a friendly user interface is established. So the whole system is highly precise, low-powered, multi-functioned, stable and easy-to-use.By experimenting and debugging, it is proved that this Intelligent Online pH Analyzer could be used to measure water's pH value. It can also store data automatically and transmit it remotely with 4-20 mA's standard electric current and RS-485 protocol. This analyzer could be widely applied in online pH value measuring of water property, and will contribute the transformation from single instrument to multi- meters controlling system.