BM280 stability

[Johanan]

Hello,

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.

Thanks

Johanan

[hor63]

Don‘t even bother further with this design approach. It will never work.

If you need to revise your PCB anyway dot it right with a differential sensor.

My educated guess is that your two sensors are not on the same PCB but one is located within the box and the other outside because the Bosch sensors do not have hose connectors. This maens it is likely that either the power supply or the ambient temperature of both sensors vary when you switch on the fans. The imperfections of the temperature compensation for absolute pressure sensors alone easily explains the diverging of the measurements.

[o_o]

hor63's point of view is a bit extreme. One thing Johanan forgot to mention was the required accuracy of the system.

If indeed the sensor system needs to detect a 10-50Pa signal, then yes this is feasible. If the sensor system needs to accurately measure it, not so much.

In a previous test comparing 2 BMP388 sensors output at rest over 2 days, I observed a typical deviation (68%) within +-3.2 Pa, and a maximum deviation (99.7%) within +-9Pa.

Therefore, I would go on to say that using 2 BMP388 absolute pressure sensor, you can detect a signal greater than 10 Pa with few false negatives.

o_o