What Is A Dissolved Oxygen Sensor?

What is a dissolved oxygen sensor?

A dissolved oxygen sensor is a device used to measure the concentration of dissolved oxygen in a liquid, usually water. Dissolved oxygen in water refers to the number of oxygen molecules dissolved in the water, which is vital to the water ecosystem and biological activities.

The role of dissolved oxygen sensor is to help us monitor the concentration of dissolved oxygen in the water body, detect water quality problems in time, and take appropriate measures. By using the dissolved oxygen sensor, we can keep abreast of the oxygen level of the water body, protect the living environment of aquatic organisms, and maintain the ecological balance of the waters.

How to measure dissolved oxygen in water?

Measuring dissolved oxygen in water is usually done using dissolved oxygen sensors. These sensors use different operating principles to measure the concentration of dissolved oxygen in water, including electrochemical sensors, optical sensors, and polarographic sensors.

• Electrochemical sensors: These sensors utilize a chemical reaction between an electrode and an electrolyte to measure dissolved oxygen. A typical electrochemical sensor consists of a redox electrode and an electrolyte solution. When dissolved oxygen comes into contact with the electrode, an oxygen reduction reaction occurs, resulting in a change in current or voltage, which is used by the sensor to determine the concentration of dissolved oxygen.
• Optical sensors: These sensors utilize optical principles to measure the concentration of dissolved oxygen. Oxygen-sensitive fluorescent dyes or optical nanomaterials are usually used as indicators. When dissolved oxygen comes into contact with the indicator, it causes a change in the emission spectrum, and the sensor detects this change to measure the concentration of dissolved oxygen.

• Polarographic sensors: These sensors utilize the redox reaction of dissolved oxygen on the surface of an electrode to measure its concentration. The electrodes in the sensor are usually made of precious metal materials, and when dissolved oxygen comes into contact with the electrodes, a redox reaction occurs that produces a current or voltage signal, and the sensor measures the concentration of dissolved oxygen based on these signals.

How dissolved oxygen sensors work?

Electrochemical dissolved oxygen sensors utilize the redox reaction of oxygen on the surface of an electrode to measure the concentration of dissolved oxygen. Such sensors typically consist of two electrodes: a working electrode and a reference electrode, both of which are immersed in an electrolyte solution.

Working electrode: The working electrode is usually made of a precious metal (e.g. platinum) covered with a catalyst. When oxygen molecules come in contact with the surface of the working electrode, an oxygen reduction reaction occurs. In the redox reaction, oxygen molecules are oxidized or reduced on the surface of the working electrode, generating an electric current.

• 氧化反应： O₂ + 2H₂O + 4e^– → 4OH^–
• 还原反应： 2H₂O + 4e^– → O₂ + 4OH^–

Reference electrode: A reference electrode is usually made of an insoluble metal (e.g., silver/silver chloride) that maintains a constant potential. The purpose of the reference electrode is to provide a stable potential reference to measure the change in current occurring at the working electrode.

When dissolved oxygen comes into contact with the surface of the working electrode, it participates in a redox reaction, generating an electric current. The sensor measures these current changes and calculates the dissolved oxygen concentration in the water from them.

Application areas of dissolved oxygen sensors

• Environmental monitoring: Dissolved oxygen sensors can be used to monitor dissolved oxygen levels in natural bodies of water (e.g. rivers, lakes, oceans). This is critical for assessing the health of water bodies, monitoring water pollution, and ecosystem restoration.
• Water quality assessment: Dissolved oxygen sensors can be used to monitor oxygen levels in water during drinking water and industrial water treatment processes to ensure that water quality standards are being met. They can also be used to assess the efficiency of wastewater treatment plants and track the degradation of organic matter in the water.
• Aquaculture: In aquaculture, dissolved oxygen sensors are used to monitor oxygen levels in aquaculture water. Proper dissolved oxygen levels are essential for the growth and survival of fish and other aquatic organisms. By monitoring dissolved oxygen levels, farmers can adjust the oxygen content of the water to improve farming efficiency and biological health.
• Biomedical: Dissolved oxygen sensors also have important applications in the biomedical field, especially in bioreactors and tissue culture. They are used to monitor oxygen levels in cell culture media to ensure proper cell and tissue growth and metabolism.

How to choose the right dissolved oxygen sensor?

There are several key factors to consider when selecting a dissolved oxygen sensor:

• Sensor types: Dissolved oxygen sensors are generally categorized into two types: membrane and electrochemical. Membrane sensors are suitable for routine water quality monitoring, while electrochemical sensors offer greater accuracy and stability for applications that require more precise measurements.
• Accuracy and stability: Choosing a dissolved oxygen sensor with high accuracy and stability is critical, especially for applications that require accurate monitoring. The accuracy and stability of the sensor has a direct impact on the accuracy and reliability of the measurement results.
• Response time: The response time of the sensor is also an important consideration. A faster response time provides real-time DO measurements, enabling users to make more timely adjustments and manage the water environment.
• Compatibility and interfaces: Consider the compatibility of the sensor with other devices, as well as its interface type. Some sensors have standard analog or digital interfaces to a variety of monitoring devices and data acquisition systems.

Summary

Dissolved oxygen sensors play a vital role in water quality monitoring and environmental management. By accurately measuring the dissolved oxygen content in a body of water, we can keep abreast of the health of the water body, protect water resources, and maintain ecological balance. Choosing the right type of sensor, and using and maintaining them correctly, ensures reliable measurements and provides accurate data to support a variety of application scenarios.

Apure offers dissolved oxygen sensors with dissolved oxygen instrumentation, in addition to instrumentation for monitoring other parameters, pressure measurement tools, level measurement tools, flow measurement tools, and temperature measurement tools. Please contact us for more information.