sensor missbehaviour

[coelner]

It is not directly related to this library itself, but maybe the right sport to discuss this:

setup: hardware    version: 12
setup: bootloader  version: 1000
setup: application version: 2000
[...]
148:    Temp: 29.51°C   Humidity: 23.67% RH Pressure: 1001.30hPa    eCO2: 1726 ppm  eTVOC: 366 ppb  
148:    Temp: 29.75°C   Humidity: 24.82% RH Pressure: 1001.30hPa    eCO2: 1625 ppm  eTVOC: 268 ppb  
baseline for this sensor: 0xEBB0
148:    Temp: 29.88°C   Humidity: 26.04% RH Pressure: 1001.29hPa    eCO2: 1621 ppm  eTVOC: 265 ppb  
149:    Temp: 30.03°C   Humidity: 24.51% RH Pressure: 1001.22hPa    eCO2: 1692 ppm  eTVOC: 330 ppb  
149:    Temp: 30.04°C   Humidity: 24.36% RH Pressure: 1001.32hPa    eCO2: 1702 ppm  eTVOC: 341 ppb  
149:    Temp: 29.79°C   Humidity: 24.80% RH Pressure: 1001.28hPa    eCO2: 782 ppm   eTVOC: 57 ppb   
149:    Temp: 30.04°C   Humidity: 23.65% RH Pressure: 1001.32hPa    eCO2: 570 ppm   eTVOC: 25 ppb   
149:    Temp: 29.65°C   Humidity: 25.73% RH Pressure: 1001.29hPa    eCO2: 423 ppm   eTVOC: 3 ppb    
149:    Temp: 29.66°C   Humidity: 24.65% RH Pressure: 1001.22hPa    eCO2: 403 ppm   eTVOC: 0 ppb    
149:    Temp: 29.69°C   Humidity: 25.42% RH Pressure: 1001.23hPa    eCO2: 405 ppm   eTVOC: 0 ppb    
149:    Temp: 29.65°C   Humidity: 23.97% RH Pressure: 1001.22hPa    eCO2: 415 ppm   eTVOC: 2 ppb    
149:    Temp: 29.70°C   Humidity: 23.55% RH Pressure: 1001.26hPa    eCO2: 402 ppm   eTVOC: 0 ppb    
149:    Temp: 29.47°C   Humidity: 23.88% RH Pressure: 1001.30hPa    eCO2: 401 ppm   eTVOC: 0 ppb    
150:    Temp: 29.31°C   Humidity: 23.96% RH Pressure: 1001.21hPa    eCO2: 403 ppm   eTVOC: 0 ppb    
150:    Temp: 28.56°C   Humidity: 24.77% RH Pressure: 1001.23hPa    eCO2: 408 ppm   eTVOC: 1 ppb    
150:    Temp: 28.93°C   Humidity: 24.37% RH Pressure: 1001.27hPa    eCO2: 412 ppm   eTVOC: 1 ppb    
150:    Temp: 28.56°C   Humidity: 24.88% RH Pressure: 1001.25hPa    eCO2: 409 ppm   eTVOC: 1 ppb    
150:    Temp: 28.32°C   Humidity: 25.19% RH Pressure: 1001.30hPa    CCS811: errstat=899=--vhXmrwF--AD-iE
150:    Temp: 28.70°C   Humidity: 25.07% RH Pressure: 1001.18hPa    CCS811: errstat=899=--vhXmrwF--AD-iE
150:    Temp: 28.63°C   Humidity: 25.25% RH Pressure: 1001.18hPa    eCO2: 466 ppm   eTVOC: 9 ppb    
baseline for this sensor: 0x9DAD
150:    Temp: 28.76°C   Humidity: 25.17% RH Pressure: 1001.27hPa    CCS811: errstat=899=--vhXmrwF--AD-iE
150:    Temp: 28.68°C   Humidity: 30.86% RH Pressure: 1001.32hPa    eCO2: 514 ppm   eTVOC: 25 ppb   
150:    Temp: 28.38°C   Humidity: 32.08% RH Pressure: 1001.28hPa    eCO2: 1961 ppm  eTVOC: 756 ppb  
151:    Temp: 27.83°C   Humidity: 32.73% RH Pressure: 1001.28hPa    eCO2: 2866 ppm  eTVOC: 2566 ppb     
151:    Temp: 27.45°C   Humidity: 33.58% RH Pressure: 1001.31hPa    eCO2: 3702 ppm  eTVOC: 4359 ppb 
151:    Temp: 27.07°C   Humidity: 34.13% RH Pressure: 1001.28hPa    eCO2: 4463 ppm  eTVOC: 5976 ppb     
151:    Temp: 26.83°C   Humidity: 34.89% RH Pressure: 1001.30hPa    eCO2: 5092 ppm  eTVOC: 7319 ppb     
151:    Temp: 26.56°C   Humidity: 35.67% RH Pressure: 1001.24hPa    eCO2: 5750 ppm  eTVOC: 8736 ppb     
151:    Temp: 26.37°C   Humidity: 36.19% RH Pressure: 1001.26hPa    eCO2: 6383 ppm  eTVOC: 10079 ppb    
151:    Temp: 26.20°C   Humidity: 36.54% RH Pressure: 1001.21hPa    eCO2: 6940 ppm  eTVOC: 11271 ppb    
151:    Temp: 26.09°C   Humidity: 36.84% RH Pressure: 1001.26hPa    eCO2: 7859 ppm  eTVOC: 13267 ppb    
151:    Temp: 25.99°C   Humidity: 36.72% RH Pressure: 1001.26hPa    eCO2: 8421 ppm  eTVOC: 14433 ppb    

I put the sensor out of the window to get the baseline. The measurement is done every second but the values get summed up for a minute. First of all, there occurs some errors because of maximum resistance was reached. After this errors the sensors was placed inside. The absolute values are far beyond useful. The sensor itself is burned-in (at least for a week) and this specific print-out was done after three hours running.

[coelner]

I have a SGP30 and CCS811 at the same spot and did some graphs. The sensor is on the window board and the bay is separated with a paper curtain from the room itself. The curtail has got a gap to the board about 3cm. Measurement is every second.

• 300s I opened a windows After 90 minutes it looks like this:
• 1566 I blow into the gap
• 1600-1650 I wiggle the curtain a little bit to simulate some air flow

[maarten-pennings]

Nice graphs.

I agree that values like eCO2: 8421 ppm eTVOC: 14433 ppb make no sense. I also cannot explain the differences between CCS811 and SGP30. The CCS811: errstat=899=--vhXmrwF--AD-iE does not raise my trust in the values.

Please do note that these sensors are TVOC sensors not CO2 sensors (the CO2 is computed from the TVOC, assuming the sensor is indoor).

[coelner]

The SGP30 (I use the sparfun library) is also not very trustworthy, sometimes it keeps the eCO2 value at 400 which can't be true. (even for a MOX sensor, which should change the resistance by blowing over it).

[maarten-pennings]

These are relative sensors.

If you take a bottle, spray a bit of alcohol in it, hang your sensor in it, close the bottle, and then switch on the sensor, it will happily report clean air (assuming you do not use the set baseline feature).

It also means that the 'zero' value is arbitrary. what the sensors typically do is take the value at power on (again, assuming you do not use the set baseline feature), and use that as reference. Typically assuming clean air, and mapping that to 400 (SGP30), 450 (CCS811), 500 (iAQcore).

By the way, I heard once, blowing on the sensor is a bit abusive. I forgot why. Maybe you cool the heater too much and it needs to step current, maybe it was the moist in your breath. Anyhow they told me not to blow, but to use a marker pen or breath some breath freshener on it.

Good luck