Oxygen sensors play a vital role in a wide range of industrial processes—from monitoring water quality to ensuring environmental compliance and maintaining process control. Whether used in liquids or gases, these sensors help monitor free oxygen levels to support safe, efficient operations.
Why Oxygen Monitoring Matters
In liquid applications like wastewater treatment, dissolved oxygen is critical for sustaining microbial life. These microorganisms are responsible for breaking down harmful compounds, and typically require at least 5 ppm (parts per million) of dissolved oxygen to survive. Maintaining the right oxygen levels is essential to the biological health and effectiveness of the treatment process.
In gas-based systems, such as those using nitrogen blanketing, oxygen levels must be kept to an absolute minimum to prevent unwanted and potentially hazardous chemical reactions. In such cases, even trace amounts of oxygen can pose a serious safety risk.
Numerous factors influence oxygen levels, including temperature, salinity, depth, bioactivity, and atmospheric pressure. Understanding and compensating for these variables is key to accurate oxygen monitoring—both in gaseous and dissolved states.
Let’s take a closer look at how oxygen sensors function and the technology behind them.
How Oxygen Sensors Work
There are two primary types of oxygen sensors used in industrial applications:
- Electrochemical (Clark-Style / Amperometric) Sensors
- Optical (Luminescent) Sensors
Each type offers distinct advantages depending on your specific process and environment.
Electrochemical Oxygen Sensors
Electrochemical sensors are ideal for applications that require the measurement of higher oxygen concentrations, capable of detecting levels up to 45 ppm. This makes them particularly suited for chemical processing and water treatment industries.
These sensors contain an oxygen-permeable membrane attached to a cathode and anode immersed in a reference electrolyte. To accurately interpret the voltage, the anode, and cathode must be polarized through a transmitter or another power source. The cathode is typically constructed of a precious metal that stabilizes the polarization of the sensor.
During in-process measurement, oxygen diffuses through the sensor’s membrane and enters the electrolyte solution. There, it undergoes a chemical reaction that generates an electrical current between the anode and cathode. The strength of this current increases with higher oxygen concentrations. A connected transmitter then converts this electrical signal into a readable oxygen value.
Optical Oxygen Sensors
Optical oxygen sensors represent a newer advancement in oxygen sensing technology and are gaining popularity across industries.
Optical sensors function using an internal LED light source and an external cap coated with an oxygen-sensitive fluorescent dye. An internal receiver monitors changes in light behavior to determine oxygen levels. In the absence of oxygen, the emitted light travels quickly between the dye layer and the receiver. When oxygen is present, it interacts with the dye, causing the light signal to slow down. These changes in signal speed are used to calculate and display accurate oxygen readings.
Sensor Maintenance: Keep It Accurate
Proper maintenance ensures reliable sensor performance and extends the life of your equipment. However, the required care varies depending on the sensor type.
Electrochemical Sensor Maintenance
Electrochemical sensors typically require more upkeep than their luminescent counterparts. To function accurately, the reference system must be polarized using a transmitter or external power source—a process that can take several hours to stabilize. Regular cleaning of the anode and cathode is also essential, especially the cathode, which is often made from a precious metal prone to wear. Without proper maintenance, the sensor’s readings may drift over time, leading to inaccurate oxygen measurements.
Optical Sensor Maintenance
The key to maintaining a luminescent (optical) oxygen sensor lies in preserving the condition of the external cap, which houses the fluorescent dye layer. Prolonged exposure to corrosive or abrasive environments can degrade this dye, leading to altered light wavelength patterns and reduced measurement accuracy. Fortunately, if the dye layer becomes compromised, the cap can be easily replaced—restoring sensor performance without the need to replace the entire unit.
Choosing the Right Sensor for Your Application
Both electrochemical and optical oxygen sensors offer unique benefits, depending on the environment and performance requirements of your application. Whether you're working in wastewater treatment, inert gas blanketing, or another oxygen-sensitive process, selecting the right sensor technology is key to maintaining operational safety and efficiency.
Explore our range of oxygen sensors to find the model that best fits your needs.