How to Determine if the Measurement of Portable Dissolved Oxygen Meter is Accurate
If there is another reliable dissolved oxygen meter, the same test water sample can be used for inspection. If not, please check as follows.
The general dissolved oxygen meter roughly conforms to the linearity of the oxygen concentration/signal output, so the two-point calibration method is generally used: 1. Use an oxygen-free water solution to check the zero point; 2. Use oxygen supersaturated water to check whether the oxygen saturation value at the current temperature is consistent with the value measured by the instrument (please check the oxygen saturation value of clean water at each temperature)
The simple steps are as follows:
1. Take a certain amount of anhydrous Na2SO3 (anhydrous sodium sulfite), and prepare a sodium sulfite solution with a mass concentration of 5% (ready to use), which is an anaerobic solution. Prepare and use immediately, otherwise oxygen will slowly dissolve into the solution, resulting in unreliable results. When operating, insert the probe of the dissolved oxygen meter into the solution, and move the probe slowly at the same time. When the reading is stable, check whether the reading is close to zero. If it is close to zero, the zero point is accurate.
2. Take a certain amount of clean water, aerate the micropores for 15 minutes, and stop the aeration, which is supersaturated water. When operating, insert the probe of the dissolved oxygen meter into the solution, and move the probe slowly at the same time. When the reading is stable, record the reading, measure the water temperature at the same time, and check the dissolved oxygen concentration table of clean water for comparison.
Note that when completing step 1, clean the probe to avoid negative errors.
Electrode Calibration of Dissolved Oxygen Meter
(1) The electrode should be cleaned once every 1 to 2 weeks. If there are pollutants on the diaphragm, it will cause measurement errors. Care should be taken when cleaning, taking care not to damage the diaphragm. Rinse the electrode in clean water. If the dirt cannot be washed off, carefully scrub it with a soft cloth or cotton cloth.
(2) The zero point and span should be re-calibrated every 2 to 3 months.
(3) Electrode regeneration is performed about once a year. When the measurement range cannot be adjusted, the dissolved oxygen electrode needs to be regenerated. Electrode regeneration includes replacing the internal electrolyte, replacing the diaphragm, and cleaning the silver electrode. If the silver electrode is observed to be oxidized, it can be polished with fine sandpaper.
(4) If the electrode leakage is found during use, the electrolyte must be replaced.
