The working principle and characteristic of dissolved oxygen

The working principle and characteristic of dissolved oxygen meter

 

Soluble oxygen meter is a polarographic analysis instrument, specially designed for boiler feedwater and condensate water PPB level dissolved oxygen measurement. Ensure the stability and accuracy in (super) low concentration, in the measurement performance and use of the environment has been greatly improved。

Dissolved oxygen meter is polarographic analysis instrument, specially designed for boiler feed water and condensate water PPB grade dissolved oxygen measurement design. Ensure the stability and accuracy in (super) low concentration, in the measurement performance and use of the environment has been greatly improved。

 

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

 

The oxygen content of water can fully indicate the degree of water self-purification. For biological treatment plants that use activated sludge, it is very important to understand the oxygen content of the aeration tank. The increase of dissolved oxygen in sewage will promote biological activities in addition to anaerobic microorganisms, so that volatile substances and ions that are easy to naturally oxidize can be removed, and the sewage can be purified。 　　

 

There are three main methods for determining oxygen content: automatic colorimetric analysis and chemical analysis measurement, paramagnetic method measurement, electrochemical method measurement, fluorescence method. The dissolved oxygen in water is generally measured by electrochemical method。 　　

 

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

 

Oxygen measurement sensors by the cathode (commonly used gold and platinum) and with current counter electrode (silver), the current reference electrode (silver), electrode immersed in the electrolyte such as KCl, KOH, sensor diaphragm cover, coated electrode and the electrolyte is separated from measured liquid, only can dissolved gas permeability of coated, so to protect the sensor, can prevent the electrolyte escape, and can prevent the foreign substances of shooting and cause pollution and poison。 　　

 

applies a polarization voltage between the reverse electrode and the cathode. If the measuring element is immersed in water with dissolved oxygen, the oxygen diffuses through the membrane and the oxygen molecules present on the cathode (excess electrons) are reduced to hydroxide ions [OH-]. Electrochemically equivalent silver chloride precipitates on the reverse electrode (insufficient electrons). For each oxygen molecule, the cathode emits 4 electrons, and the reverse electrode receives them, forming a current: 4Ag+4Cl-=4AgCl+ 4E -.

 

The size of the current is proportional to the partial pressure of oxygen in the measured sewage. The signal, together with the temperature signal measured by the thermal resistance on the sensor, is sent to the transmitter. The oxygen content in the water is calculated by using the relationship curve between the oxygen content stored in the sensor, the oxygen partial pressure and the temperature, and then converted into a standard signal output. The function of the reference electrode is to determine the cathode potential。

 

Dissolved oxygen meter has the characteristics of easy installation, long calibration period (3~4 months), insensitive to other substances, and can monitor the use of electrolyte in the film and probe, electrolyte and film replacement usually every one to three years。