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Forced Recalibration of SCD 30 CO2 sensor
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Forced Recalibration of SCD 30 CO2 sensor

by Paulo11 on Sun May 09, 2021 1:00 pm

Hi every one
I am a beginner with Arduino

I tried to calibrate SCD 30 CO2 sensor with fresh and the reference 400

I used the Adafruit SCD30 library with the sketch sensor tuning (thanks Adafruit!)

I uncomment a part of the sketch

So I have

if (!scd30.forceRecalibrationWithReference(400)){
Serial.println("Failed to force recalibration with reference");
while(1) { delay(10); }
}

Now, with fresh air, the measure is 530 ppm


I also obtain


Adafruit SCD30 Sensor adjustment test!
SCD30 Found!
Measurement interval: 2 seconds
Ambient pressure offset: 0 mBar
Altitude offset: 300 meters
Temperature offset: 3.00 degrees C
Forced Recalibration reference: 400 ppm
Self calibration disabled

Do you know where is my mistake?

Thank you very much

Paulo11
 
Posts: 2
Joined: Sat May 08, 2021 8:00 pm

Re: Forced Recalibration of SCD 30 CO2 sensor

by blnkjns on Sun May 09, 2021 1:52 pm

The reference on Hawaii is 420ppm, which is considered Earth background amount. You will only find 400 in a greenhouse.
If you are in a city, outdoor air can be easily 500 thanks to the CO2 dome effect of cities with even higher peaks near busy roads. Where are you located?
Besides, you basically use the sensor in a relative fashion. Absolute readings are less interesting.

blnkjns
 
Posts: 630
Joined: Fri Oct 02, 2020 3:33 am

Re: Forced Recalibration of SCD 30 CO2 sensor

by Paulo11 on Sun May 09, 2021 2:32 pm

Thank you for your answer

Of course, only the différence is important but if the calibration isn't good in fresh air, (near 400 ppm) il will be worse near 1200.

I tried to calibrate in the country, far from a town, where an other sensor gives between 390 and 410

If I force the calibration with fresh air and the value 400 and if I understand coorectly the calibration , I must fin s400 in the same fresh air , isn't il?

Paulo11
 
Posts: 2
Joined: Sat May 08, 2021 8:00 pm

Re: Forced Recalibration of SCD 30 CO2 sensor

by blnkjns on Mon May 10, 2021 12:46 am

What is the other sensor? 390 is also impossibly low, background CO2 is 419 now.
https://www.esrl.noaa.gov/gmd/ccgg/tren ... tml#global
https://www.esrl.noaa.gov/gmd/ccgg/trends/weekly.html
Isn't forced calibration just a forced offset? You could as well do in post to your data. Many sensors just store the 24-hour lows and offset to the history of that to match 400, which is crazy in a way as well, as that is the 2016 situation.
If you look at the data sheet, the relative accuracy is high, the absolute is not, so if you built in a daily offset to the lowest you pull from the website I gave, you will be better off than using internal calibration (read: internal offset).

blnkjns
 
Posts: 630
Joined: Fri Oct 02, 2020 3:33 am

Please be positive and constructive with your questions and comments.