3 ms·

Yes. It is important to use CO2 sensors that do not have a short automatic baseline calibration like the MH-Z19 that is popular in DIY projects but calibrates e

Yes. It is important to use CO2 sensors that do not have a short automatic baseline calibration like the MH-Z19 that is popular in DIY projects but calibrates every 24h. Better use a sensor like the Senseair S8 that only calibrates every 8 days and you most likely have a weekend of low occupancy that should bring CO2 down to ambient levels.

5e92cb50239222b 5y ago
I haven't been able to open a window for about a month due to extreme air pollution outside, and I think my Senseair S8 is broken now. If it sees fresh air with normal CO₂ levels it goes from "normal" 1.5-2k PPM (which are really closer to 4k) to zero and then shoots up to ~65000 PPM, and stays there. It spent the last two weeks in a room with an open window and still shows 65k PPM. Does anyone know of any way to recalibrate it, except for the obvious solution of putting it in a closed box and slowly lowering the amount of CO₂ there?
- janekm 5y ago
  There is a calibration pin which you can connect to GND for 4-8s to force a manual calibration (if you can bring the sensor into an environment of ~400ppm): https://emariete.com/en/meter-co2-esp8266-nodemcu-sensor-senseair-s8/ https://emariete.com/en/meter-co2-esp8266-nodemcu-sensor-sen...
- ahaucnx 5y ago
  I think 65k ppm is outside the measurement range of the S8. It might be a communication or code issue that causes this and not from actual measurements.
- nemetroid 5y ago
  According to its datasheet, the S8 reports CO2 level as a 16 bit integer, so values around 2^16 (65535) sound like underflow issues.
ysleepy 5y ago
You can set the calibration mode to manual using either the serial port or a pin on the mh-z19. Mine is configured to manual and after a few months it still reads reasonable values for outside air. But yes, the default is autocalibration. But honestly, the difference isn't that bad, it's probably like 100ppm offset for stale room air from outside, and 100 doesn't make a huge difference when you are trying to measure around 1500.

5e92cb50239222b 5y ago

I haven't been able to open a window for about a month due to extreme air pollution outside, and I think my Senseair S8 is broken now. If it sees fresh air with normal CO₂ levels it goes from "normal" 1.5-2k PPM (which are really closer to 4k) to zero and then shoots up to ~65000 PPM, and stays there. It spent the last two weeks in a room with an open window and still shows 65k PPM. Does anyone know of any way to recalibrate it, except for the obvious solution of putting it in a closed box and slowly lowering the amount of CO₂ there?

janekm 5y ago
There is a calibration pin which you can connect to GND for 4-8s to force a manual calibration (if you can bring the sensor into an environment of ~400ppm): https://emariete.com/en/meter-co2-esp8266-nodemcu-sensor-senseair-s8/ https://emariete.com/en/meter-co2-esp8266-nodemcu-sensor-sen...
ahaucnx 5y ago
I think 65k ppm is outside the measurement range of the S8. It might be a communication or code issue that causes this and not from actual measurements.
nemetroid 5y ago
According to its datasheet, the S8 reports CO2 level as a 16 bit integer, so values around 2^16 (65535) sound like underflow issues.

ysleepy 5y ago

You can set the calibration mode to manual using either the serial port or a pin on the mh-z19. Mine is configured to manual and after a few months it still reads reasonable values for outside air. But yes, the default is autocalibration. But honestly, the difference isn't that bad, it's probably like 100ppm offset for stale room air from outside, and 100 doesn't make a huge difference when you are trying to measure around 1500.