Online dissolved oxygen controller is an important equipment for water quality monitoring, and its measurement accuracy directly affects the decision-making quality of scenarios such as aquaculture and sewage treatment. Regular calibration is the core link to ensure data reliability. The following provides a comprehensive analysis of the calibration process from principle to practice:
1、 Preparation and preprocessing before calibration
Electrode activation and polarization
New electrodes or electrodes that have not been used for a long time need to be polarized with electricity: connect the instrument and power on for 3060 minutes. If restarted within 1 hour of shutdown, polarization will take 525 minutes. This step forms a stable potential difference in the electrolyte, laying the foundation for accurate measurement.
Cleaning and Inspection
If the electrode is contaminated (such as algae adhesion, oil stains), it needs to be washed with alkaline water, 0.01mol/L hydrochloric acid, etc., and then thoroughly washed with running water.
Check the integrity of the film layer and replace it immediately if it is damaged or aged.
Environment and equipment preheating
Soak the electrode in water for 12 hours, connect the signal converter, and preheat it with electricity for at least 30 minutes to ensure circuit stability.
2、 Core calibration process
zero point calibration
Solution preparation: Dissolve approximately 25g of anhydrous sodium sulfite in distilled water and add distilled water to 500mL (ready to use).
Operation steps: Dip the electrode into the zero point calibration solution, wait for the reading to stabilize, and then start the calibration program to reset the displayed value to zero.
Range calibration
Preparation of saturated dissolved oxygen solution: At (25 ± 0.5) ℃, air is introduced into distilled water at a flow rate of 1L/min until the dissolved oxygen is saturated, and the solution is allowed to settle (510 minutes for 200mL water and 1020 minutes for 500mL water).
Calibration execution: Immerse the electrode in the range calibration solution, stir until the reading stabilizes, measure the current water temperature, and adjust the instrument reading against the standard dissolved oxygen concentration meter.
Iterative optimization: Repeatedly alternate between zero and range calibration until both errors are controlled within ± 0.25mg/L.
3、 Special scenario calibration technology
Salinity compensation calibration
In high salinity environments, it is necessary to enter the "Salt mode" and modify the preset value (default 0.0g/L) according to the actual salinity.
Pressure compensation calibration
Enter "Air mode" and modify the instrument preset value (default 101.3kPa) based on the local real-time atmospheric pressure to eliminate the influence of air pressure on dissolved oxygen concentration.
4、 Maintain standards and quality control
calibration cycle
It is recommended to calibrate once a month under normal operating conditions; The high load or severe fluctuation environment needs to be shortened to weekly and mandatory calibration should be carried out after each electrode replacement.
Operation taboos
Avoid air bubbles from adsorbing onto the sensor membrane surface, and gently wipe in a single direction when wiping.
Throughout the calibration process, avoid direct sunlight and heat interference to maintain a constant water temperature.
Calibration is not only a technical process, but also a core component of the quality management system. Through the above systematic operation, the authenticity and scientific decision-making of online dissolved oxygen data can be guaranteed.