A research team led by Choe Chol Min, a researcher at the Faculty of Electronics, has developed a real-time ozone meter to measure ozone concentration at disinfection stations and transmit measured values to the control board of an ozone generator through RS-485(Modbus RTU).
In general, several methods such as chemical titration, spectrophotometry, ultraviolet absorption, chemical luminescence, chemical fluorescence and electrochemical analysis are used for measurement of ozone concentration.
Electrochemical analysis is based on the Faraday's law which explains that current generated from electrochemical reduction of ozone at a work electrode inside a sensor is proportional to the concentration of ozone.
The meter based on electrochemical analysis is composed of a sensing circuit, a filtering and amplifying circuit, a communication circuit, a display circuit, a power source stabilizing circuit and a microprocessor.
At disinfection stations, ozone meters are affected by a strong electromagnetic field from several pieces of electronic equipment such as an ozone generator. In other words, sensing signals are affected by several high frequency noises as well as the source noise and this leads to a big error in the measured value without elimination of the noise. As sensing signals are DC signals, they eliminated the source and high frequency noises with the help of a low-pass filter. In order to prevent the effect of cable resistance and cable noise on the signals, they designed the meter so that they could be converted into 1kHz signals and transmitted to the meter.
They built two communication circuits in the meter. One is a communication circuit which uses V-F conversion to prevent the attenuation of sensing signals in case of the distance of more than 30m between the meter and the sensor. The other one is RS-485 circuit which transmits measured values to the control board. The main circuit and the source circuit are separated from each other, which ensures the stability of the communication circuit.
They also wrote a program to display exact values of ozone concentration and CT and to transmit CT values to the control board by RS-485(Modbus RTU).
The characteristics of the developed meter are as follows.
Measurement index: ozone concentration, CT
Measurement range: 0~200ppm
Relative error: below 5%FS
Relative standard deviation: below 2% (n=11)
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