Bandpass Filters for CO2 Detection

CO₂ molecules absorb infrared light strongly at specific wavelengths due to their vibrational-rotational energy transitions. The primary absorption band for CO₂ is around 4.26 µm (micrometers). NDIR sensors exploit this property:

• IR light passes through a gas sample.

• CO₂ molecules absorb light at 4.26 µm, attenuating the signal.

• The amount of attenuation correlates with CO₂ concentration via the Beer-Lambert Law

Active Filter (Detection Channel)

• Centered at the absorption peak of the target gas (e.g., 4.26 µm for CO₂).
• Measures the attenuation of IR light caused by the gas absorbing energy.

Reference Filter (Compensation Channel)

• Centered at a wavelength unaffected by the target gas (e.g., 3.9 µm for CO₂).
• Provides a baseline signal to account for non-gas-related changes (e.g., light source intensity, dust, or humidity).