Definition
A dissolved oxygen tester is an analytical instrument used to determine the amount of dissolved oxygen in a liquid. Dissolved oxygen usually refers to the concentration of molecular oxygen dissolved in water or other liquids, and its measurement is often expressed in milligrams per liter or percentage saturation. The instrument has a wide range of application values in environmental monitoring, aquaculture, industrial process control and scientific research.
How it works:
Mainstream dissolved oxygen testers use electrochemical or optical sensing principles. Electrochemical sensors usually contain a cathode, an anode, and an electrolyte, and oxygen diffuses into the sensor through a selective membrane, where a reduction reaction occurs to produce a current signal that is directly proportional to the partial pressure of oxygen. Based on the principle of fluorescence quenching, the optical sensor emits fluorescence after a specific substance is excited, and its fluorescence life or intensity has a quantitative relationship with oxygen concentration.
Measurement method
Common measurement methods include laboratory analysis and continuous monitoring in the field. Laboratory analysis can be carried out with portable instruments for point sampling and determination, and attention should be paid to avoid contact between the sample and air during operation. On-site monitoring mostly uses online instruments, which can achieve long-term continuous data collection. Regardless of the method, calibration is carried out according to the relevant standard procedures, usually using zero-oxygen solution and air-saturated water as calibration points. The measurement process needs to record the water temperature and atmospheric pressure, because the oxygen solubility decreases with the increase of temperature, the relationship can be expressed by the following formula:
Cs = 14.6 - 0.39T + 0.01T2
where Csis the saturated dissolved oxygen value, and T is the water temperature.
Influencing factors
Measurement accuracy is affected by several factors. Temperature changes can alter oxygen solubility and sensor response characteristics, and modern instruments are often equipped with automatic temperature compensation. Salinity affects the solubility of oxygen, and salinity correction is required for high-salinity samples. The liquid flow state affects the oxygen diffusion rate on the membrane surface, and the appropriate flow rate can ensure the measurement stability. Sensor membrane integrity is critical, and breakage or contamination can lead to slow response or biased readings. Regular maintenance includes electrolyte replacement, cleaning of optical windows, and verification of calibration curves.
Applications:
In water environment monitoring, it is used to evaluate the self-purification capacity and ecological health of water bodies. The aquaculture industry ensures the living environment of farmed organisms by monitoring dissolved oxygen. In wastewater treatment processes, dissolved oxygen data is used to optimize the operational efficiency of aeration systems. In the process of food and beverage production, dissolved oxygen control is related to product quality and shelf life. In addition, it has specific applications in the fermentation industry, power system water chemistry monitoring and other fields.
Instrument selection
When selecting a model, it is necessary to comprehensively consider the measurement range, accuracy requirements and environmental conditions. Portable instruments are suitable for multi-point patrol inspection, while online instruments are suitable for long-term continuous monitoring. In the presence of chemically interfering substances, optical sensors may be more adaptable than electrochemical sensors. For deep-sea or high-pressure environments, a special pressure-compensated model is required. The protection level of the instrument should meet the requirements of the site environment, while considering data interface compatibility and maintenance convenience. Users can refer to relevant national standards and international norms to select instruments with corresponding performance parameters based on specific application scenarios.