I am conducting a study to detect whether or not emissions come out of an electric vehicle using the Arduino and a gas sensor. I have the MQ-131 gas sensor connected, as well as an LCD to output the values when not connected to a laptop. The MQ-131 should be detecting NOx, CL2 and O3, according to the datasheet. I have left the sensor on for several hours trying to burn it in, but not the recommended 24 hours.
As of right now, the code for the sensor is just outputting the analogRead(), which isn't in PPM or PPB yet. I believe the output I am seeing is the resistance, which has values ranging from 0 to 1023. Anyways, whenever I try testing the sensor by exposing it to some ozone producing equipment, the value decreases, instead of increasing. That confuses me so much, and I was wondering if anyone could shed light on why the values would go down. What I am assuming, is that the resistance(0-1023) should go up if it senses any gases that it was made to detect. Am I right in assuming that?
I am thinking once I have that understanding, I am going to try calibrating the MQ-131 as much as I can, since the MQ-131 isn't exactly the greatest tool for accurately detecting specific gases and the densities. For now I just need to get the values to increase in what I assume is the presence of NOx or O3.
Thanks for the help!