My organisation purchased a Grove Multichannel Gas sensor from Digi-Key in the UK to measure pollution levels. We have been having problems with measuring nitrogen dioxide levels. The wiki page for this sensor says that the nitrogen dioxide level cannot go over 10ppm, but we have been regularly getting much higher values:
The NO2 values being reported by the sensor are not realistic, especially considering that the air pollution is lower than usual at the moment due to the lockdown. As you can see from the graph showing the levels for a 24 hour period, it is also reporting that the levels increased dramatically overnight, whereas you would expect the opposite to be true.
The sensor was last calibrated in February, and it is currently up on the side of a building so it would be difficult to calibrate it again.
It is connected to an Arduino Pro Mini via I2C and being powered by 3.3v. It was programmed using the Arduino IDE and the library provided by Seeed.
We suspect that the sensor is faulty, or do you have any other idea why the nitrogen dioxide is so high?
you have the same problems with v2 … why you sell this crap ?.. WIth your NOX Values on both sensors everybody would died instantly… its no funny to order 2 sensor for 100 bucks for testing your crap
I am facing a similar problem using the V2 Sensor. As you see in the screenshot, the NO2 values are unrealistic high. Values above 700 ppm would lead to sudden death.
Therefore, I have some questions:
Is the unit of the values probably ppb instead of ppm?
What is the measurement range of the sensor? I couldnt find the range in the provided specifications
Is it possible to perform a self calibration or in general a calibration of the sensor? How is this done?
My ‘solution’ with the V1 sensor was to just assume that the values are in ppb instead of ppm as you say (even though the specifications say ppm). I then also divided the values by 4 to get the averages to roughly match up with the averages recorded by our local council.
The specifications for the V1 sensor claim it can measure NO2 from 0.05 to 10ppm but we have had values far above this somehow. I couldn’t find anything for V2 either.
With the V1 at least, there was a calibration script included with the Arduino library. It can be found under File > Examples > Multichannel Gas Sensor > calibration. I set up the script and then left it outdoors for around half an hour, but it didn’t seem to help much with getting realistic values.
It seems that unfortunately these sensors just aren’t very good at measuring NO2 - we are still getting strange anomalies and our values don’t correlate with values recorded by other air quality monitors.
