CO₂ sensor

[mht]

I am using PAS CO2 sensor in single shot mode. Power up sequence: +3.3V , then +12V, then wait minimum 1s.

PWM_DIS connected to 3.3V, PSEL connected to GND. 

I trigger a measurement every minute, enabling ABOC in the field BOC_CFG (register MEAS_CFG). [write 0x05 into MEAS_CFG]

Then I wait minimum 2 seconds, and afterwards I read out the measurement value. Outdoor (country side, clean air) I get values around 800ppm. Whether I enable or not the ABOC, the measured values seem to be the same. 

Am I missing something? 

In the end I assumed there is a sensor offset of ~400ppm, and I subtracted it from the measured values. Is this a valid approach?  

[AditiB_81]

Hi,

Can you share the logs/measurement data with different setup changes?

Thanks

Aditi

[AjayB_76 · Accepted solution]

Hi, 

1. To utilize the ABOC the sensor needs to be running in continuous mode of operation. The sampling rate can be varied in continuous mode between 1 meas/ 5s and 1 meas/ 4095 secs.
2. ABOC kicks in after 1 week of operation. If 1 week operation period is not an option, then we recommend to do Forced Compensation at the beginning and enable the ABOC for future correction.

Please refer to the following app note which has details of ABOC:

App note

In the end I assumed there is a sensor offset of ~400ppm, and I subtracted it from the measured values. Is this a valid approach?  
yes, if the sensor is exposed to outside CO2 concentration, the offset has to be subtracted. 

[AjayB_76 · Accepted solution]

In the end I assumed there is a sensor offset of ~400ppm, and I subtracted it from the measured values. Is this a valid approach?  
yes, if the sensor is exposed to outside CO2 concentration, the offset has to be subtracted. 

[mht]

Now it is clear. Thank you! 

I did read all available documentation on this sensor before starting. The document: https://www.infineon.com/dgdl/Infineon-Registermap_description_PASCO2_MA2-ApplicationNotes-v02_00-EN... has a note at BOC_CFG register stating "in single shot mode, ABOC correction factor is applied...", which I understood as "the offset is automatically subtracted, only it is not updated over time". 

I am targetting a battery operated device, therefore I have to cut off power completely between measurements. I'll have to handle the sensor offset drift in software.