1. The amount of dissolved oxygen in the salt water in the solution is significantly lower than that in tap water. For accurate measurement, the effect of the amount of salt on the dissolved oxygen must be considered. In the case of constant temperature, the dissolved oxygen decreases by about 1% for every 100 mg / L of salt content. If the salt content of the solution used by the meter during calibration is low, but the salt content of the actual measured solution is high, it will also cause errors. In actual use, the salt content of the measurement medium must be analyzed in order to accurately measure and compensate correctly.

    2. Influence of temperature Due to the temperature change, the diffusion coefficient of the membrane and the solubility of oxygen will change, which directly affect the current output of the dissolved oxygen electrode. Thermistors are often used to eliminate the effect of temperature. As the temperature rises, the diffusion coefficient increases and the solubility decreases. The effect of temperature on the solubility coefficient a can be estimated according to Henry's law, and the temperature on the membrane diffusion coefficient β can be estimated by Arrhenius' law.

    3. Flow rate of the sample The diffusion of oxygen through the membrane is slower than that through the sample. It must be ensured that the electrode membrane is completely in contact with the solution. For the flow-through detection method, the oxygen in the solution will diffuse into the flow cell, so that the oxygen in the solution near the membrane will be lost, which will cause diffusion interference and affect the measurement. For accurate measurement, the flow rate of the solution flowing through the membrane should be increased to compensate for the oxygen lost by diffusion. The minimum flow rate of the sample is 0.3 m / s.

    4. Influence of atmospheric pressure According to Henry's law, the solubility of a gas is proportional to its partial pressure. The partial pressure of oxygen is related to the altitude of the area. The difference between the plateau area and the plain area can reach 20%. Before use, it must be compensated according to the local atmospheric pressure. Some instruments are equipped with a barometer inside, which can be automatically calibrated during calibration; some instruments are not equipped with a barometer, and must be set according to the data provided by the local weather station during calibration. If the data is incorrect, it will cause a large measurement error