The working principle and characteristics of the dissolved o

The working principle and characteristics of the dissolved oxygen meter

 

Core tips: dissolved oxygen analyzer is a polarographic analysis instrument, specially designed for ppb level dissolved oxygen measurement of boiler feed water and condensate. It ensures the stability and accuracy in (ultra) low concentration, and greatly improves the measurement performance and use environment。

Dissolved oxygen analyzer is a polarographic analysis instrument, specially designed for ppb level dissolved oxygen measurement of boiler feed water and condensate. It ensures the stability and accuracy in (ultra) low concentration, and greatly improves the measurement performance and use environment。

 

Dissolved oxygen meter is mainly used for continuous monitoring of dissolved oxygen in chemical fertilizer, metallurgy, environmental protection, pharmaceutical, biochemical, food and tap water solutions。

 

The oxygen content in water can fully show the degree of water self purification. For the biological treatment plant using activated sludge, it is very important to know the oxygen content of aeration tank. The increase of dissolved oxygen in sewage will promote biological activities other than anaerobic microorganisms, thus removing volatile substances and ions easy to be oxidized naturally, so that the sewage can be purified。 　　

 

There are three methods to determine oxygen content: automatic colorimetric analysis and chemical analysis, paramagnetic method, electrochemical method and fluorescence method. Dissolved oxygen in water is usually measured by electrochemical method。 　　

 

Oxygen can be dissolved in water, and the solubility depends on temperature, total pressure and partial pressure of water surface and salts dissolved in water. The higher the atmospheric pressure, the greater the ability of dissolved oxygen in water. The relationship is determined by Henry's law and Dalton's law. Henry's law holds that the solubility of gas is directly proportional to its partial pressure。 　　

 

The oxygen measurement sensor is composed of cathode (commonly made of gold and platinum), counter electrode (silver) with current and reference electrode (silver) without current. The electrode is immersed in electrolyte such as KCl and KOH. The sensor is covered with a diaphragm. The membrane separates the electrode and electrolyte from the measured liquid. Only dissolved gas can penetrate the membrane. Therefore, the sensor is protected and electrolyte escape is prevented In addition, it can prevent the invasion of foreign substances and lead to pollution and poisoning。 　　

 

When a polarization voltage is applied between the counter electrode and the cathode, if the measuring element is immersed in water with dissolved oxygen, oxygen will diffuse through the diaphragm, and the oxygen molecules appearing on the cathode (excess electrons) will be reduced to hydroxyl ion [OH -]. For each oxygen molecule, the cathode emits four electrons, and the counter electrode receives electrons, forming a current of 4ag + 4CL - = 4agcl + 4E -.

 

The current is proportional to the partial pressure of oxygen in the tested sewage. The signal is sent to give the transmitter along with the temperature signal measured on the sensor's thermal resistance. The oxygen content in the effluent is calculated by simultaneous interpreting the relationship between the oxygen content and the temperature of the oxygen stored in the sensor, and then converted to standard signal output. The function of reference electrode is to determine the cathode potential。

 

The dissolved oxygen analyzer has the advantages of easy installation, long calibration period (3-4 months) and insensitivity to other substances. It can also monitor the usage of electrolyte in the coated and probe, and generally replace the electrolyte and coated once every one to three years。