In the dissolved CO ₂ sensor, NDIR (non dispersive infrared) and fluorescence methods are the two core technologies, which respectively rely on the principles of optical absorption and fluorescence quenching to construct a high-precision and high stability monitoring system.
NDIR technology: infrared absorption based on molecular "fingerprint"
The core of NDIR technology lies in utilizing the strong absorption properties of CO ₂ molecules towards specific wavelengths of infrared light. When the 4.26 μ m wavelength light emitted by the infrared light source passes through a gas chamber containing CO ₂, gas molecules selectively absorb the wavelength light, and the remaining light intensity is received by the detector after passing through a narrowband filter. According to Lambert Beer's law, the degree of light intensity attenuation is linearly related to the concentration of CO ₂. Sensors can accurately calculate the concentration by detecting changes in light intensity and inverting them through algorithms. For example, the WS300 sensor adopts a dual channel design, which achieves real-time self calibration by measuring the difference in light intensity between the channel and the reference channel, eliminating factors such as light source attenuation and environmental interference, and has excellent long-term stability. Its core advantage lies in its strong anti-interference ability, suitable for scenarios such as food and beverage, environmental monitoring, etc. However, it has a large volume and requires regular cleaning of the air chamber to prevent contamination.
Fluorescence method: rapid response based on fluorescence quenching
Fluorescence sensors achieve measurement by detecting the energy transfer effect after the collision of fluorescent substances with CO ₂ molecules. The fluorescent reagent (such as ruthenium complex) coated on the surface of the probe emits red light under blue light excitation, while CO ₂ molecules quench the fluorescence, resulting in a shortened fluorescence lifetime. Sensors measure changes in fluorescence lifetime and calculate concentration using the Stern Volmer equation. For example, fluorescence based dissolved oxygen sensors have achieved a response time of 30 seconds, while CO ₂ sensors also have fast response characteristics and do not require electrolytes or oxygen permeable membranes, resulting in low maintenance costs. Its core advantage lies in its compact size and lack of consumables, making it suitable for portable detection, soilless cultivation, and other scenarios. However, its accuracy is slightly lower than NDIR and it is susceptible to strong light interference.
Technical comparison and selection suggestions
NDIR technology is known for its high precision and long lifespan, making it suitable for fixed installation scenarios; Fluorescence law is characterized by fast response and maintenance free, making it more suitable for dynamic monitoring needs. The actual selection should be based on the requirements of the scenario: electrochemical sensors can be prioritized for low to medium precision scenarios such as sewage treatment; High precision scenarios such as food and beverage, biomedicine, etc. require NDIR or fluorescence sensors.