FAQ - CO2 Sensors

CO2 Sensors

We have summarized the frequently asked questions about our CO2 sensors.
We hope that this information will be helpful. If the problem persists, please contact us.

[A-01] Refer to CO2 Sensor Lineup page.

[A-02] ppm is the acronym for Parts Per Million, which is a unit of measurement. Indicates how many parts per million.

For example, 1mm within 1km is 1ppm. 1% = 10,000ppm.

[A-03] During the usage of  the sensor, the accuracy will drop due to a decrease in the amount of light emitted by the light source, a decrease in the sensitivity of the light receiving element, or deterioration of the light path itself. Vibration during transportation and handling and stress on the circuit board also cause fluctuations.

The performance of the sensor can be maintained by performing periodic calibration. All the sensors of Senseair have a built-in self-calibration feature, the ABC (Automatic Baseline Correction) algorithms.


  • ABC (Automatic Baseline Correction) Calibration: This type corrects the minimum CO2 level measured over time to 400 parts per million. The 400ppm concentration is said to be the CO2 concentration of fresh outside air.
  • Zero Calibration: This type calibrates at a point of a measured value of 0ppm by using a reference gas that does not contain CO2 (e.g., 100% nitrogen gas).
  • Background Calibration: This type calibrates at a point of measured value of 400ppm by using a reference gas with a CO2 concentration of 400ppm.

ABC (Automatic Baseline Correction) calibration

CO2 exists all around us, and fresh air is said to have a CO2 level of about 400ppm. CO2 sensors are programmed to register the lowest COconcentration values over a period of time (default: 8 days) and to perform zero adjustment if a difference is detected from the outside air CO2 concentration of 400ppm.

For a typical indoor situation, the CO2 concentration of the outdoor air drops at some point within week. The ABC algorithm, however, does not work in a plastic greenhouse or an indoor environment where humans are constantly active, as the CO2 levels do not drop to the CO2 levels found in the air outdoors. If this happens, turn off the ABC function and calibrate the unit every two to three years. Zero calibration kits are also made available by Senseair.

[A-05] Generally, the two-sensor system includes a sensor that is sensitive to the absorption wavelength of the gas to be measured and a reference sensor. The output of the reference sensor, which is not affected by the gas concentration to be measured, enables estimation of the changes in the light source and the light path, thereby enabling the correction to be made.

By comparison, the one-sensor system is designed to measure only the absorption wavelength of the target gas, requiring fewer components and therefore, is effective in reducing the component cost and variations among individual units. Performance can be maintained by periodic calibration even without a reference sensor.

[A-06] Be careful not to block the gas inlet where the particle filter is installed. For other handling precautions, refer to the handling manual for each product.

[A-07] The response time of NDIR type gas sensors is dominated by the rate at which the gas naturally diffuses into the enclosure. The response time can be reduced through the quicker replacement of the gas in the enclosure by designing the surrounding environment. For example, installation of an intake fan will be effective.

[A-08] The sensor is designed not to react to any other gases besides CO2. Specifically, an optical filter that selectively transmits the absorbed wavelength of CO2 is attached to the infrared sensor of the light-receiving element.

[A-09] Use the product in an environment where there is no dew condensation. Condensation may cause water droplets to adhere to the surface of the infrared light receiving/emitting component or the inner wall surface of the enclosure, resulting in changes in the optical path and consequently significant fluctuations of the measured values.

[A-10] Because the range depends on the location where the CO2 sensor is installed and on the airflow, the space range cannot specified. In order to find the optimum installation location, we recommend carrying out various trials such as simulating airflow and actually performing measurement in various locations.

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About Senseair

Senseair, which became a member of the Asahi Kasei Microdevices (AKM) Group in 2018, is a provider of gas sensors using NDIR: Non-Dispersive InfraRed technology. Our goal is to constantly develop and mass-produce new gas sensor technologies.