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Advantages of the XENSIV™ PAS CO2 sensor over eCO2 – KBA234983

Advantages of the XENSIV™ PAS CO2 sensor over eCO2 – KBA234983

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Community Translation: eCO2 に対する XENSIV™ PAS CO2 センサーの利点 – KBA234983

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Infineon’s XENSIV™ PAS CO2 sensor is based on the Photo Acoustic Spectroscopy (PAS) technology and measures the actual concentration of CO2. So, this sensor can also be referred to as a true CO2 measurement sensor. These sensors are very accurate and comparative performance details are available in the application note.

Typically, eCO2 sensors in the market are metal oxide (MOx)-based sensors that use pre-established models to derive the concentration of CO2 based on conductivity changes of other gases that are typically present along with CO2 and hence called Indirect CO2 measurement sensors. They are not as accurate as True CO2 measuring sensors. 

  1. Lab measurement

The measurement results as seen in Figure 1 show the response of eCO2 and true CO2 sensors when the concentration of CO2 is changing.  An error in the measurement is visible, which happens because eCO2 sensors are not measuring the actual concentration of CO2.

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Figure 1:  eCO2 sensor response to different CO2 concentrations

Some of the eCO2 sensors are also susceptible to changes in humidity. Figure 2 shows that for the same concentration of CO2, concentration levels differ at different levels of humidity.

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Figure 2:  eCO2 sensor response at different levels of humidity

In summary, the eCO2 sensors have an inferior performance compared to the true CO2 sensors.

  1. Use case measurement

MOx sensors do not react to CO2; in the real world, there is no correlation between other gases like H2 and volatile organic compounds, and CO2. The algorithm is usually simplified and therefore gives inaccurate results as seen in Figure 3.

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Figure 3:  Response of XENSIVTM PAS CO2 and eCO2 sensors compared to the reference sensor output

Here, the response of the PAS CO2 sensor is compared with responses of two eCO2 sensors and then with the CO2 levels detected using a reference sensor. The PAS CO2 sensor closely follows the reference sensor behavior, but the eCO2 sensor performance has a higher margin of error. It can also be seen that eCO2 sensors miss the peak values of CO2 concentration,  which is not desirable. The mode of sensing used in the eCO2 sensor is the reason for this poor performance. Therefore, it can be stated that the eCO2 sensor is not suited for either absolute or relative measurements.

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