What is dissolved oxygen meter?
Dissolved oxygen meter
is an instrument for measuring the oxygen content in water based on the electrochemical principle that a redox reaction will be generated at two different metal electrodes in the electrolyte solution containing oxygen, and the resulting diffusion current and the concentration of oxygen in the solution are related to each other. Some instruments are also made by the principle that the current on the polar spectrum generated by applying voltage to the working electrode in the solution is related to the concentration of the measured substance in the solution, using the polar spectrum method in voltammetry.
Dissolved oxygen meter application
Use dissolved oxygen meter to ensure the respiratory needs of aquatic organisms, real-time monitoring of oxygen content as well as automatic alarm, automatic oxygenation and other functions.
Natural water quality monitoring
Dissolved oxygen sensor can detect the degree of pollution of waters, self-purification ability, and prevent biological pollution such as eutrophication of water bodies.
Wastewater treatment, control indicators
Dissolved oxygen meter anaerobic tank, aerobic tank, aeration tank with other indicators used to control the effect of water treatment.
Control of industrial water supply pipeline metal material corrosion
Generally with ppb (ug / L) level range of sensors, control pipelines inside to achieve zero oxygen, to prevent rust, commonly used in power plants, boiler equipment.
How does dissolved oxygen meter work?
Dissolved oxygen sensor
is an instrument for measuring the oxygen content in water based on the electrochemical principle that a redox reaction will be generated on two different metal sensors in an electrolyte solution containing oxygen, and the resulting diffusion current is related to the oxygen concentration in the solution. Some instruments use the Ji-spectrum method of voltammetry, where the voltage applied to the working sensor in the solution generates a current on the Ji-spectrum that is related to The measured substance in the solution is the concentration of the substance. Dissolved oxygen sensors can be used to measure the dissolved oxygen content in the aqueous solution of the sample under test in the field or the laboratory. Since dissolved oxygen is one of the main indicators of water quality, dissolved oxygen sensors can be widely used for measuring dissolved oxygen content in various settings, especially in cultured water, photosynthesis, and respiration and in the field. When assessing the ability of stream and lake water to support biological survival, biochemical oxygen demand (BOD) tests are performed, which measure oxygen-consuming sample water solutions containing organic matter as they become putrefied, and determine the relationship between dissolved oxygen concentration and the temperature of the sample water solution. Its measurement range: is 0 to 5, 10, 20 mg/L, accuracy ± 3% to ± 5%, and response time of about 30 to 120 s. There are two categories: online continuous monitoring and laboratory instrumentation.
Components of dissolved oxygen meter
Dissolved oxygen meter consists of a host and an oxygen electrode. The e-oxygen electrode (also called oxygen-sensitive film electrode) consists of two metal electrodes in contact with the supporting electrolyte and a selective film (i.e., oxygen film). Using advanced fluorescence measurement principle, no membrane and electrolyte, basically no maintenance, no oxygen consumption during measurement, and no flow rate/agitation requirements; With NTC heating function, the measurement results have good repeatability and stability.
Dissolved oxygen meter types
Classification of dissolved oxygen meters by principle
Polar spectrum dissolved oxygen meter
Most of the dissolved oxygen meters
on the market now are polar spectrum analyzers, ppm level can be widely used in chemical fertilizer, environmental protection, pharmaceutical, biochemical, food and tap water as well as other liquids, for continuously measuring dissolved oxygen levels. ppb level is designed for power plants, boiler feed water and condensate, etc. ppb level dissolved oxygen measurement is designed, which ensures stability and accuracy at (ultra) low concentrations, in terms of measurement performance and use environment, etc. Nowadays, the technology has been greatly improved.
Most common dissolved oxygen meters use diaphragm electrode as transducer, which converts dissolved oxygen concentration (actually oxygen partial pressure) into electrical signal, then amplified, adjusted (including salinity, temperature compensation), and displayed by analog-to-digital conversion.
There are two types of membrane electrodes used in dissolved oxygen meters: Polarography and primary cell type 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 a potassium chloride solution. The cathode's outer layer is covered by an oxygen-permeable film. The film can be used in polytetrafluoroethylene, polyvinyl chloride, polyethylene, silicone rubber, and other breathable materials.
Fluorometric dissolved oxygen meter
For more than 50 years, oxygen measuring meter has been measured by the current and polarographic methods. This method used to play a very important role in dissolved oxygen monitoring in municipal and industrial wastewater, however, the traditional electrochemical method use membranes, electrodes, and electrolyte, which can lead to many problems, and even with regular maintenance, accurate measurement results are still not obtained.
The innovative new fluorescence technology, without membrane and electrolyte, is almost maintenance-free, with excellent performance and ease of use. The fluorescence dissolved oxygen meter is based on the principle of physics of sudden quenching of active fluorescence by specific substances.
Fluorescence method dissolved oxygen meter, first developed by foreign countries and put into use, in China in the 1990s by state support, belongs to the national ninth five-year key research topics, after more than ten years of research and production technology has become mature.
The fluorescent material in the front of the sensor is a special platinum metal porphyrin compounded with a polyester foil that allows the passage of gas molecules, the surface is coated with a layer of black light barrier material to avoid the interference of daylight and other fluorescent substances in the water. The sapphire window is isolated from the red and blue light sources and the photoreceptors in the watertight titanium housing. The modulated blue light shines on the fluorescent material to excite it and emits red light. Since oxygen molecules can take away energy (sudden extinction effect), the excitation time and intensity of red light are inversely proportional to the concentration of oxygen molecules. We used a red light source synchronized with the blue light as a reference, measured the phase difference between the excited red light and the reference light, and compared it with the internal calibration value, to calculate the concentration of oxygen molecules, and output the final value after linearization and temperature compensation.
Classification of dissolved oxygen meters by portability
Portable dissolved oxygen meter
Desktop dissolved oxygen meter
Pen dissolved oxygen meter
Classification of dissolved oxygen meters by application
Laboratory dissolved oxygen meter
Industrial online dissolved oxygen meter
Classification of dissolved oxygen meters by degree of functionality
Economic dissolved oxygen meter
Intelligent dissolved oxygen meter
Precision Dissolved Oxygen meter
Pointer-type dissolved oxygen meter
Digital display type dissolved oxygen meter
How to calibrate dissolved oxygen meter?
First observe whether the film is broken at the electrode bubble, if there is a broken condition, the original electrode bubble needs to be replaced, add electrolyte to the new electrode bubble, replace it to the electrode, and then wipe the electrode dry.
Weigh 5.00g of anhydrous sodium sulfite solid, dissolve it with distilled water and prepare 100mL of 5% zero calibration solution.
Press "ON/OFF" key to turn on the power, wipe the electrode dry and carefully absorb the water on the film.
Put the dissolved oxygen electrode into 5% sodium sulfite solution, and when the instrument is in the measurement state (the word CONC is displayed in the lower left corner), press the
Press "▲/mg.L-1/%" or "▼/Storage" to select "ZERO" (lower left corner of the display) and press "OK/Print " key, the instrument enters the zero oxygen calibration function. After the reading is stable, press "OK/Print", the instrument will display "0.00mg/L", and the instrument will exit "ZERO" state automatically after about 5 seconds.
Remove the electrode and wipe it dry, put it on the platform, press "▲/mg/L-1/%" or "▼/Storage" to select "FULL" (bottom left corner of the display). The instrument enters the full oxygen calibration function, press "OK/Print". After the reading is stable, press "OK/Print" key, the instrument will display the current dissolved oxygen value, about 5 seconds later, the instrument will automatically exit the "FULL" state.
Repeat steps 2-6 twice until the calibration is stable.
How to use dissolved oxygen meter?
Calibration: The probe of dissolved oxygen meter is connected to the main unit and placed in a dissolved oxygen bottle, which is filled with about 3cm high pure water. Then follow the calibration steps to calibrate.
Measurement: After the dissolved oxygen meter is calibrated, place the probe in the sample, turn on the stirring switch, wait for the temperature and dissolved oxygen reading to stabilize, and read the reading.
Shutdown: After the sample measurement, rinse the dissolved oxygen meter probe with deionized water, place it in the BOD bottle, and turn off the host switch.
How to maintain dissolved oxygen meter?
Portable dissolved oxygen meter electrodes should be cleaned once every 1 to 2 weeks. If there are contaminants on the diaphragm, it will cause measurement errors. Care should be taken when cleaning, and be careful not to damage the diaphragm. Put the electrode into clean water and wash it, if the dirt cannot be washed away, scrub it carefully with a soft cloth or cotton cloth.
The zero point and range of the dissolved oxygen meter should be recalibrated once in 2~3 months.
The regeneration of the dissolved oxygen meter electrode should be carried out about once a year. When the measurement range is not adjusted, it is necessary to regenerate the dissolved oxygen electrode. Electrode rejuvenation consists of changing the in-house electrolyte, changing the membrane, and washing the silicon electrodes. If oxidation is observed in the silver electrode, polish it with fine sandpaper.
If the dissolved oxygen meter electrode is found to be leaking during use, the electrolyte must be replaced.
Precautions for using dissolved oxygen meter
1. The dissolved oxygen instrument should be waterproof during use, especially when calibrating, the water droplets outside the probe membrane should be dried with absorbent paper.
2. Dissolved oxygen meter should wait for at least 15 minutes after power on to make the probe polarization and temperature stabilization, if the calibration code is done too early the calibration value will drift and may exceed the technical requirements.
3. Dissolved oxygen measurement is strongly correlated with room temperature, and the ambient temperature should be kept stable at about 20℃.
How to buy dissolved oxygen meter?
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