Hello everyone,
I have a problem understanding how to calibrate the gas sensor mq 135 and mq 131. I use arduino nano. I'm getting some values, but I don't know if they are correct. My goal is to measure the CO2 values and ozone values in the air.
Can anyone help me how to calibrate these sensors? I have preheated these sensors for 48 hours and I don't know how to proceed further.
FYI i don´t have access to chamber with these gases, can i also do calibration in the fresh air?
Thank you.
You can use outside air as a reference point for CO2, ~400ppm.
Air filtered by activated carbon filter would give you 0ppm reference for ozone.
For other references you need known concentration of those gases or calibrated measuring instrument.
Hey,
thank you for your response. In my case i would need step-by-step tutorial how to calibrate my sensors. Is there any other advice how to do it?
Adafruit offers a great general tutorial on sensor calibration.
Unfortunately the MQ series of sensors are not stable, and not intended for accurate calibration.
Furthermore they all respond to several different gases or contaminants, so with just one sensor, it is impossible to say for sure what a change in reading means, if you don't know which contaminants are present.
The sensors are intended at best to warn you if something in the environment has changed.
Thank you 
