4 ms·
> But after a few weeks, and after adding in a manual temperature adjustment to compensate for that sensor's inaccuracy, the AirGradient has been a very stable
by danans 5y ago
> But after a few weeks, and after adding in a manual temperature adjustment to compensate for that sensor's inaccuracy, the AirGradient has been a very stable and helpful addition to my home environment monitoring.
When you are DIYing this sort of thing, I would think you would need to make at least a couple of them to see if they calibrate to the same measurement, assuming what you are after is greater precision and control (why else would you DIY it?). Even then, both devices could calibrate to the same very imprecise value.
To really validate this, you would need to put it in an controlled environment with known air pollution levels. Just placing it outdoors when the weather report says 200AQI wouldn't work since that's an average over a large area, not a point measurement.
I imagine the sensor manufacturers have done some calibration - the article mentions a self calibration period for some, but once everything is in the final package, I'd expect the behavior to change.
- ashtonkem 5y agoMost of the DIY solutions I’ve seen use pre-packaged PM sensors, which are probably the same parts embedded in over the counter solutions.
- danans 5y agoYes, but has the final assembly been calibrated against a known controlled environment? Without that, the readings from the device become more of a crapshoot, which is fine if there is no desire for greater precision (i.e a just for fun project) Sensor manufacturers cannot calibrate for every possible packaging configuration. As someone who has DIYed a lot of stuff related to indoor climate, I tend to save my effort for the mitigation work, and use well tested measurement tools to validate those. This is for the same reason that one doesn't usually DIY a multimeter before doing electrical work.
- ashtonkem 5y agoThe PM sensor I’m thinking of comes in it’s own packaging with a fan, and is usually attached to a PCB alone. I don’t see how most applications of it would require a recalibration.
- geerlingguy 5y agoI have two identical boards now, along with my TemTop portable unit, and the CO2 is quite close (< 1% difference usually), and PM2.5 readings are more like 5-10% different. The temperature is the biggest outlier, but I need to figure out a better placement for the temperature sensor to get that issue fixed.
- asdff 5y agoWith this data it seems like you'd be more concerned with the relative value and its change over time anyhow rather than the true value.
- jiveturkey 5y agoyup. not entirely useless, but especially for the borderline yellow/orange AQI you want to know the error. http://www.aqmd.gov/aq-spec http://www.aqmd.gov/aq-spec tests and compares commercial AQM vs lab grade instruments. It isn't quite enough to compare a commercial unit with the same sensor, because you don't really know the mfr calibration (if any), but this will get you a much better idea of performance. i personally prefer to have a commercial sensor that has an API, rather than DIY.