I. Calibration method of dissolved oxygen meter: Generally, the dissolved oxygen meter can be calibrated by standard liquid or on-site sampling.

    1. Dissolved oxygen meter standard solution calibration method: Standard solution calibration generally uses two-point calibration, that is, zero-point calibration and span calibration. The zero calibration solution can use 2% Na2SO3 solution. The span calibration solution can choose 4M KCl solution (2mg / L); 50% methanol solution (21.9mg / L) according to the measuring range of the instrument.

    2. On-site sampling and calibration method of dissolved oxygen meter (Winkler method): In actual use of dissolved oxygen meter, Winkler method is often used for on-site calibration of dissolved oxygen analyzer. There are two cases when using this method: the meter reading is M1 when the sample is taken, and the analysis value is A. When the meter is calibrated, the meter reading is still M1. At this time, you only need to adjust the meter reading to be A. The meter reading when sampling is M1, laboratory analysis value is A. When the meter is calibrated, the meter reading is changed to M2. At this time, the meter reading cannot be adjusted to A, but the meter reading should be adjusted to 1MA × M2.

    2.Use and maintenance of dissolved oxygen meter electrode

The electrode of the dissolved oxygen meter should be cleaned once every 1 to 2 weeks. If there is a contaminant on the diaphragm, it will cause measurement errors. Take care when cleaning, taking care not to damage the diaphragm. Put the dissolved oxygen meter electrode into clean water and rinse it. If the dirt cannot be removed, wipe it carefully with a soft cloth or cotton cloth.

In February, February and March, you should re-check the zero point and range of the dissolved oxygen meter electrode.

    3. The regeneration of the dissolved oxygen meter electrode is performed about once every one 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 of the dissolved oxygen meter is found to be leaking during use, the electrolyte must be replaced.

    Ⅲ. Polarization of dissolved oxygen electrode

When used for the first time or continuously powered off for more than 5 to 10 minutes, polarization is performed after the instrument is connected and powered on. In order to make the chemical system in the electrode reach equilibrium, reduce the zero oxygen current and make the electrode stable. At the beginning, the current of the electrode is large, it decreases exponentially, and it is in a stable state after 6 hours. The displayed data during this period will gradually decrease until it stabilizes. Calibration can only be performed later.

The polarization process takes 6 hours. Connect the electrode to the secondary meter correctly first, and then connect the meter power. If the power-off time is not long, the polarization time will be shorter and the stability will be faster