Measuring Factors of Online Dissolved Oxygen Meter
One: The factors measured by the online dissolved oxygen meter are as follows:
1. The influence of temperature As the temperature changes, the diffusion coefficient of the membrane and the solubility of oxygen will change, which will directly affect the current output of the dissolved oxygen electrode. A thermistor is often used to eliminate the influence of temperature. As the temperature rises, the diffusion coefficient increases, but the solubility decreases instead.
2. The influence of temperature on the solubility coefficient can be estimated according to Henry's law, and the temperature on the membrane diffusion coefficient can be estimated through Arrhenius' law.
3. Solubility coefficient of oxygen: Because the solubility coefficient a is not only affected by temperature, but also by the composition of the solution. Under the same oxygen partial pressure, the actual oxygen concentration of different components may also be different.
4. Effect 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%, and it must be compensated according to the local atmospheric pressure before use.
5. Some instruments of the online dissolved oxygen meter are equipped with a barometer inside, which can be automatically corrected during calibration; some instruments are not equipped with a barometer, and should be set according to the data provided by the local weather station during calibration. large measurement error.
6. Salt content in the solution The dissolved oxygen in brine is significantly lower than that in tap water. In order to measure accurately, the influence of salt content on dissolved oxygen must be considered. Under the condition of constant temperature, dissolved oxygen decreases by about standard for every standard increase in salt content.
7. If the solution used by the meter for calibration has a low salt content, but the actually measured solution has a high salt content, it will also cause errors. In actual use, the salt content of the measurement medium must be analyzed for accurate measurement and correct compensation.
8. The flow rate of the sample Oxygen diffusion through the membrane is slower than that through the sample, so it is necessary to ensure that the electrode membrane is in complete contact with the solution. For the flow-through detection method, the oxygen in the solution will diffuse into the flow cell, causing the loss of oxygen in the solution close to the membrane, resulting in diffusion interference and affecting the measurement.
