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The difference between membrane method dissolved oxygen and fluorescence method dissolved oxygen meter

by:BOQU     2023-04-11
The working principle of the membrane dissolved oxygen method is different from that of the fluorescence method. The common membrane dissolved oxygen meter mostly uses a diaphragm electrode as a transducer to convert the dissolved oxygen concentration (actually oxygen partial pressure) into an electrical signal, which is then amplified and adjusted ( Including salinity, temperature compensation), displayed by analog-to-digital conversion. There are two types of practical membrane electrodes for dissolved oxygen meters: polarographic (Polarography) and galvanic cell (Galvanic Cell). Polarography: In the electrode, a gold (Au) ring or a platinum (Pt) gold ring is used as the cathode; silver-silver chloride (or mercury-mercurous chloride) is used as the anode. The electrolyte is potassium chloride solution. The outer surface of the cathode is covered with an oxygen-permeable film. The film can adopt breathable materials such as polytetrafluoroethylene, polyvinyl chloride, polyethylene, silicone rubber, etc. The fluorescence dissolved oxygen sensor is based on the principle of quenching active fluorescence by specific substances in physics. The blue light from a light-emitting diode (LED) shines on the fluorescent material on the inner surface of the fluorescent cap, and the fluorescent material on the inner surface is excited to emit red light. By detecting the phase difference between the red light and the blue light, and comparing with the internal calibration value Comparison, so as to calculate the concentration of oxygen molecules, and output the final value after automatic compensation of temperature and air pressure. Fluorescence dissolved oxygen analyzers have more advantages. The membrane method is easily covered by sludge, and the sludge has little effect on the fluorescence DO measurement. The fluorescence method for measuring dissolved oxygen does have the advantages of faster response and longer use time than the polarographic method, but the price of the fluorescence method dissolved oxygen meter is more expensive. Advantages of Fluorescence Dissolved Oxygen Meter over Membrane Method The traditional membrane dissolved oxygen meter needs to change and clean the probe frequently due to the membrane and electrolyte, and the data is easy to drift. Fluorescence dissolved oxygen measurement does not require frequent cleaning of the probe, the data is stable, and the measurement response time is fast. The effect is to save energy and ensure the degradation effect. In summary, the fluorescence dissolved oxygen analysis has the following advantages. 1. No calibration required. Because it is designed by fluorescence method. Therefore, calibration is not required, which greatly reduces the maintenance workload during instrument use. 2. The measurement result is stable. The measurement of dissolved oxygen by fluorescence method is more stable because it does not consume any substance and does not consume dissolved oxygen in water during the measurement process. 3. Reduce cleaning frequency. The traditional membrane method needs to be cleaned frequently, otherwise it will seriously affect the penetration of oxygen and thus affect the measurement. The fluorescence method does not require high cleaning of the probe, just wipe the fluorescent cap regularly. 4. Low maintenance. Because the fluorescence method does not require calibration, frequent calibration, replacement of membrane (RO membrane), and frequent cleaning, the amount of maintenance after installation and use is very small. 5. No interference. Changes in pH value, chemical substances contained in sewage, H2S, heavy metals, etc. will not interfere with the measurement. In addition, it is also oxidizing and may be measured as oxygen by ordinary dissolved oxygen electrodes; carbon dioxide entering the electrolyte will The impact on the measurement is mainly to change the conductivity of the electrolyte, and the LDO has no electrolyte, so it will not be affected by carbon dioxide. 6. Fast response time. Fluorescent dissolved oxygen responds as soon as it comes into contact with water, and the time is very short. 7. No need for polarization time. Since no electrodes are used, there is no problem of polarization.
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