Definition
A dissolved oxygen meter is an analytical instrument used to measure the concentration of dissolved oxygen in liquids. Dissolved oxygen refers to molecular oxygen dissolved in water or other liquids, and its concentration is one of the key parameters for evaluating the environmental quality of water bodies, biochemical reaction processes and industrial process control. The instrument converts oxygen concentration into a readable signal through sensors, which is widely used in environmental monitoring, aquaculture, sewage treatment, food and beverage production, and scientific research.
Principle
The measurement core of a dissolved oxygen meter is based on electrochemical or optical principles. The electrochemical principle usually uses a Clark-type electrode, which consists of a cathode, an anode, and an electrolyte, covered with a breathable membrane. Oxygen diffuses into the electrode through the thin film, and a reduction reaction occurs at the cathode, generating a diffusion current proportional to the oxygen concentration, and the dissolved oxygen concentration is calculated by measuring the current value. The optical principle is based on the fluorescence quenching effect, the fluorescent substance on the surface of the sensor fluoresces under the excitation of a specific wavelength of light, and its fluorescence life or intensity is affected by the quenching effect of oxygen molecules in the environment, and the oxygen concentration is indirectly determined by detecting changes in fluorescence signal.
Measurement method
Dissolved oxygen measurement is mainly divided into two methods: in-situ measurement and laboratory measurement. In-situ measurement immerses the sensor directly into the liquid to be measured for real-time monitoring, which is suitable for continuous monitoring in the field. Laboratory measurements are analyzed under controlled conditions after sample collection, and attention should be paid to avoid oxygen exchange during sample collection and storage. Calibration is a critical step in ensuring accurate measurements, typically using zero-point versus full-scale calibration: zero-point calibration uses an oxygen-free solution, and full-scale calibration uses air-saturated water or a standard solution with a known oxygen concentration. Measurements are often expressed in milligrams per liter or percentage of saturation, and conversion takes into account temperature and salinity corrections.
Influencing factors
Dissolved oxygen measurement is affected by a variety of environmental and operational factors. Temperature changes directly affect the solubility of oxygen and the response speed of the sensor, and most instruments are equipped with temperature compensation functions. The liquid flow rate affects the oxygen diffusion balance on the surface of the breathable membrane, and maintaining an appropriate flow rate helps stabilize the measurement. Salinity changes change oxygen solubility and require salinity correction when measuring seawater or high-salt samples. Sensor status such as membrane integrity, electrolyte consumption, and electrode contamination can cause reading deviations and require regular maintenance. In addition, the change of atmospheric pressure has an impact on the calculation of saturated dissolved oxygen, and pressure correction should be paid attention to when measuring at high altitudes.
Application:
In the field of environmental monitoring, dissolved oxygen meters are used to evaluate the self-purification capacity and ecological health of rivers, lakes and oceans, and are the core indicators of routine water quality monitoring. In aquaculture, dissolved oxygen concentration directly affects the survival of aquatic organisms, and continuous monitoring can help optimize oxygenation control and improve aquaculture efficiency. The sewage treatment process adjusts the aeration volume by monitoring the dissolved oxygen in the aeration tank, so as to optimize the biochemical treatment process and control energy consumption. The food and beverage industry monitors dissolved oxygen in fermentation, filling, and other processes to ensure product quality and shelf life. In addition, dissolved oxygen measurement also provides data support for process control and experimental analysis in chemical production, power system water cycle, and scientific research.
Selection
When choosing a dissolved oxygen meter, you should consider the measurement needs and environmental conditions. For long-term continuous monitoring, it is advisable to choose sensors with high stability and long maintenance cycles, and consider anti-biological adhesion and corrosion-resistant designs. Laboratory intermittent measurement can focus on instrument accuracy and ease of operation. Select the sensor type according to the characteristics of the medium: the optical sensor is not easily disturbed by flow rate and does not need to replace the electrolyte frequently, and is suitable for occasions with low flow rate or interfering substances such as hydrogen sulfide; Electrochemical sensors have relatively low cost and fast response, making them suitable for routine water quality monitoring. In addition, it is necessary to pay attention to whether the calibration function, data recording ability, protection level and output interface of the instrument meet the system integration requirements. It is recommended to refer to relevant industry standards and on-site verification results for comprehensive evaluation.