Design And Implementation Of COD Online Monitoring Instrument

As environmental pollution has already affected the social production as well as the nation's sustainable development, nation starts to make a plan that it detects the water pollution of key point river basin on line in the real time during Twelfth Five Years Plan. The Chemical Oxygen Demand (COD) is a comprehensive indicator which is used to evaluate the water degree of contamination. So, it is very important to detect a place with water's COD on-line all day long.This paper provides a method how to design the COD online monitoring based on electrochemical sensor. The core of system mainly discusses the intelligent automation of machine, setting high-resolution and constant voltage for sensor using stoping technology, getting the high-accuracy and high-resolution current signal using Flexible_Switch rang and Two-Stage amplifier technology.By means of the compare with different COD detecting methods, this paper selects hydroxyl radical oxidized electrochemistry method. The part of system construct is composed of system whole framework design and process flow analysis. The hardware design concludes the details introduction of power circuit design, reliable potentiostatic circuit design and kinds of driver circuit design. The software design parts include lower machine software design in the keil environment and upper machine software design in the WinCE 5.0. The lower machine software mainly controls the electrochemical sensor, collects the signal of sensor and communicates with upper machine. The upper machine software achieves the data process, system device control and communication and friendly exchange with user.Using the electrochemical sensor equivalent model, we can get the machine which has the 1mV voltage resolution, 1nA current resolution and 99.9% accuracy in theμA cuurent. In the different glucose solution, it has good linear relation (R2=0.9939 and R2=0.9913) between COD and measured current.The results indicate the COD online monitoring instrument has a good measurement effect. The whole COD online monitoring instrument can do very well for the 48 hours continuous test.