Measurement of absolute values using comparative detection with two detector elements
Conventional CO2 sensor modules employing a single detector element assume a reference value of 400ppm in unoccupied space and use the relative value detection, measuring CO2 concentrations by calculating the difference from the reference value. In actual environments in which occupants are present 24/7, CO2 concentrations never fall to the 400ppm reference value, resulting in measurement errors due to the difference between true CO2 concentration and the reference value.
To solve this problem, the CDM7160 employs two detectors with different optical filters in front of each detector. One detector measures the intensity of infrared light passing through the optical filter, transmitting only the infrared wavelength region absorbed by CO2 (CO2 absorption wavelength). The other detector measures the intensity of infrared light passing through the optical filter, transmitting only the infrared wavelength not absorbed by CO2 (i.e. a reference wavelength), and is thus unaffected by the constant presence of CO2.
Cost-effective single light source, dual wavelength sensor
NDIR CO2 sensors are broadly classified into three types - Single light source, single wavelength; Dual light source, dual wavelength; and Single light source, dual wavelength.
The single light source, dual wavelength system employed by the CDM7160 measures light intensities at two different wavelengths after separation by two optical filters, thus compensating drift due to accumulated dust and contamination. This ensures long-term stability, minimum maintenance, and high cost-effectiveness.