I have a few of these sensors, but lately I have been concentrating on a MQ131 ozone sensor module from SainSmart. I am building an array utilizing MQ gas sensors and an Arduino that can be attached to a drone to measure vertical concnentration profiles of ground level ozone.
I am using an ozone generator and a 2B Technologies Ozone Monitor for the calibration of the sensor.
I have done the 24 hour burn in period on my sensors.
I have warmed them up to get steady values on my serial monitor.
The problem that I am having is that I am creating nearly 20,000 ppb O3 and the analog output is only around 25 to 30 units. It works out to around 922 ppb per unit.
Example before ozone is added the sensor reading is steady at 41. After raising the concentration of O3 to 18,727.5 ppb the reading drops to around 17-18.
Recently I have added a 22,000 ohm resistor in series with the analog output so that my readings start out at 971. But I am still only dropping around 20 units to 951 when ozone levels rise to nearly 20,000 ppb.
My question is how do I use a larger range of the units. There are 1023 possible values and I would like to see my reading drop from 971 to maybe the 200 area so that I am using more of the range. I would like each unit to be worth about 0.5 ppb. Ambient outdoor concentrations very rarely go higher than maybe 150 ppb so with the setup I have that would not even register on the serial output.
Thank you in advance for any help.