Introduction;
The online dissolved oxygen meter ensures stability and accuracy at (ultra) low concentrations, and has greatly improved measurement performance and usage environment.
The dissolved oxygen meter is mainly used for continuous monitoring of dissolved oxygen values in solutions in chemical fertilizer, metallurgy, environmental protection, pharmaceutical, biochemical, food, and tap water industries.
Working Principle;
The oxygen content in water can fully indicate the degree of water self-purification. For biological treatment plants using activated sludge, it is very important to know the oxygen content in the aeration tank. An increase in dissolved oxygen in sewage promotes the activity of organisms other than anaerobic microorganisms, thus removing volatile substances and ions that are easily oxidized naturally, thereby purifying the sewage.
There are mainly three methods for measuring oxygen content: automatic colorimetric analysis and chemical analysis measurement, paramagnetic method measurement, electrochemical method measurement, and fluorescence method. The dissolved oxygen in water is generally measured by the electrochemical method.
Oxygen can dissolve in water, and the solubility depends on temperature, total pressure on the water surface, partial pressure, and dissolved salts in the water. The higher the atmospheric pressure, the greater the ability of water to dissolve oxygen. The relationship is determined by Henry's law and Dalton's law. Henry's law states that the solubility of a gas is proportional to its partial pressure.
The oxygen measurement sensor consists of a cathode (usually made of gold and platinum), a counter electrode with current (silver), and a reference electrode without current (silver). The electrodes are immersed in an electrolyte such as KCl or KOH. The sensor is covered with a membrane that separates the electrodes and electrolyte from the measured liquid. Only dissolved gases can permeate the membrane, thus protecting the sensor, preventing electrolyte escape, and preventing contamination and poisoning from foreign substances.
A polarization voltage is applied between the counter electrode and the cathode. If the measuring element is immersed in water containing dissolved oxygen, oxygen will diffuse through the membrane, and oxygen molecules appearing at the cathode (excess electrons) will be reduced to hydroxide ions [OH-]. Electrochemically equivalent silver chloride precipitates on the counter electrode (insufficient electrons). For each oxygen molecule, the cathode releases 4 electrons, and the counter electrode accepts electrons, forming a current: 4Ag+4Cl-=4AgCl+4e-.
The magnitude of the current is proportional to the partial pressure of oxygen in the measured wastewater. This 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 using the relationship curve between oxygen content, oxygen partial pressure, and temperature stored in the sensor, and then converted into a standard signal output. The function of the reference electrode is to determine the cathode potential.
Features;
The dissolved oxygen meter has the characteristics of easy installation, long calibration cycle (3-4 months), insensitivity to other substances, and can monitor the usage of the membrane and electrolyte inside the probe. Generally, the electrolyte and membrane are replaced every one to three years.
Technical Parameters;
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Measurement range:
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0～1000ug/L; 0～20.00mg/L (auto switch); 0～60℃;
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Resolution:
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0.1ug/L; 0.01mg/L; 0.1℃;
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Basic error:
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ug/L: ±1.0%FS; mg/L: ±0.5%FS, temperature: ±0.5℃;
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Repeatability:
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±0.5%FS;
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Stability:
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±1.0%FS;
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Temperature compensation:
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0-60℃ automatic compensation;
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Output signal:
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Isolated 4-20mA current loop, RS-485 communication;
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Alarm relay:
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Two alarm relays with adjustable upper/lower limits;
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Power supply:
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AC220V±10%, 50Hz;
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Working environment:
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Temperature: 0-60℃; Humidity: ≤90%RH;
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Dimensions:
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96×96×110mm (panel cutout: 92×92mm);
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