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Senseair CO2 Sensor Pressure Dependence

Posted by Mark Lemon on

All infrared (NDIR) CO2 sensors have a dependence on pressure. This is because of the physics principle used to measure CO2 concentration.

The NDIR type of sensor measures the IR radiation absorbed by CO2 molecules, which corresponds to the mole concentration. When pressure increases, the number of molecules in a given volume also increases linearly. Conversely, when pressure decreases (higher altitudes, for example) the number of molecules decrease.

This app note includes both general information about Senseair sensors and pressure, as well as the equation for computing true CO2 level readings at various pressures useful for any NDIR CO2 sensor.

Click here to read or download the app note (pdf).

Note that like CO2 sensors, oxygen sensors are also pressure and altitude dependent. We had a client in Bangalore, India purchase a CM-0505 O2 Data Logger. He reported that it was reading 18.3% instead of the expected 20.9% when exposed to outdoor ambient air.
I looked up the Bangalore, India Airport information and found that the altitude was 2,890 feet above sea level. Using this chart we found online, we were able to confirm for the client that in fact, his meter was performing within the expected tolerances.


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