Post by wbp on Oct 9, 2019 16:09:34 GMT -8
I started another thread about this but it ended up being more about the 3d parts, so I wanted to start a thread specifically about the orientation of the PPD42 Air Quality sensor. When I first set up my SkyWeather, I was seeing a lot of zero data for AQI. I also have a couple of Purple Air AQI devices that I have been doing some testing with. They are not cheap, and considered to be pretty accurate - they use a pair of SM5003 laser dust sensors. The two that I currently have are producing numbers that match pretty well. Not so much the numbers from the AQI sensor in the SkyWeather...
Some research led me to documentation that says the PPD42 is intended to be installed vertically, not horizontally as with the default SkySensor kit and 3d printed housing. The PPD42 has two air slots, one intake, the other outlet, and there is a small resistor that gets heated up to create air flow. With the device on it's side, there won't be much airflow. So I designed a new housing that puts it in the correct position. With the PPD42 oriented vertically beneath the Budd box, I am now getting AQI numbers that correlate quite well with the PurpleAir sensors that I have, at least so far.
It's probably also worth mentioning that the open area in the PPD42 is not supposed to be exposed to light. I guess it's open so it can be cleaned easily, but in use if light gets into that area the counts won't be very accurate. I covered it with some black gaffer tape, but you could also print the enclosure for it with black material (like Proto Pasta's excellent CF PLA).
Running the test program "testDust.py" I used to get a lot of zeros. Now I don't get any zeros, and the numbers I am seeing for PM2.5 look really good.
Will
