To sum up :
The air quality egg outputs 2 values per sensor – the raw resistance measured, and a interpretation of that based on a number of factors including a average calibration value (R0), humidity, temperature and a factory supplied set of graphs helping to turn the raw resistance value into a ppb (Parts per billion) value for human consumption.
So these are the values from our AQE (Now placed outside in a semi rural placing)
and these are the values from another AQE in the UK (also placed outside in a rural setting)
and as you can see – the raw resistance is not that far apart taken over time, but the interpreted values are extremely far apart.
I would expect both of these to show very small CO values, and there is clearly something wrong in the delta between the 2 interpreted graphs.
I suspect mine is wrong – as the values are way too high, especially seeing it’s windy outside, and the air “feels” good to me.
The manufactures of the AQE has a blog posting about how to set the R0 (or calibration resistance) of the egg to change the calculations – so that is one way of correcting the interpreted values, but it is a bit cumbersome, as it requires you to upload new software to the Arduino clone, running it, and the re-uploading the base station software. For experimentation this seems a bit long winded.
What I feel is needed is software to do this on my own computer – so I may have to sit down and get cracking on this – after all this is the real advantage of all the open source software!