I am trying to measure the pressure inside a box (about 1x1x1 meters), which has a few fans taking air out.
The measured range is 10 to 50 pa. I use 2 BMP280 devices, one outside the box, one inside the box.
I calibrate the difference when no fan is on, I get 0 pa.
Whoever after some time, there is a drift, which I cant explain. I read the data sheet many times, and it seems that I should be able to get an accurate measurement, but I have seen drifts of 30 pa difference with no fan working on a stable system.
I am using "Ultra high resolution" prs oversampling x16, Temp. Over sampling x2, IIR coefficient x16, and I even add my own IIR of x32 is my software. Sample delay is 0.5ms , as power consumption is not an issue.
Stile, I have this drift.
What am I missing? Is there some particular PCB layout needed (I followed all recommendations on data sheet, my PCB has only 3 mounting holes and so on.
IMHO you have chosen a bad design from the start.
the pressure difference is at the lower end of the resolution of the absolute pressure sensors.
You should use a differential pressure sensor with an appropriate rage ( e.g. 100PA). Here your pressure difference is the full range of the sensor, and not a minuscule part like in your design.
Well, you are correct that I am starching it, but I am still within the data sheet specifications.
according to my settings, in ultra high resolution, and IIR cof. I set, the nois in pressur measurment shuld be 0.2 pa.
I avarge this more by my own IIR, and still get fluctuations 3 pa, and slow drifts of 6 - 8 pa in a short time.
So I wonder if the data sheet is inaccurate, or I am doing something wrong, or I misunderstand the data sheet.
Price of differential sensors for this range is much higher then BMP280 or BMP388.