Ozone PPB sensor output goes down when ozone PPB goes up in real life about arduino-mq131-driver

[ostaquet]

Dear OIdnewbold,
I didn't have the chance to test the sensor in a lab environment. I tested it by using the sensor outside in clear air and compare with results from a local air quality station.

According to the specification, the sensor conductivity gets lower along with the gas concentration rising. It means that the resistance (Rs) increase while the gas concentration is higher. To be accurate, it's important that the R0 is correctly calibrated. In my experience, I saw crazy output if the preheat period of 48 hours is not respected.

So, we have Rs increasing. So, Rs/R0 is increasing and according to the sensitivity curves, it gives us the concentration based on the formula defined in the Excel file.

I honestly don't see why your sensor is working backwards... except if it's not a MQ131 (a lot of Winsen sensors, like the MQ7, are working on the other way: if gas concentration is increasing, the resistance is becoming lower).