BMP388 Altitude Reading Nowhere Near Accurate

#1

Hello, I have purchased a BMP388 from you the other day and have just received it today. I am now testing it and have come across a big problem. Using a simple test script - making sure the sea level pressure is accurate etc. I get an altitude reading of 200m, which is a lot considering the highest point in my county (Norfolk) is 103m and my altitude is about 16m (I think). Could I have received a dodgy sensor or could there be another problem?

Thanks,
Louis

#2

Aaah checking several websites for local sea level pressure gives me different results but I am still 15m or so off now. All websites say different to the first very inaccurate one I looked at.

#3

Still about 15 metres off, is this normal?

#4

The closest airports QNH reading should be as good as it gets for atmospheric pressure adjusted to mean sea level.

#5

How are you connecting it (and what to?), which library are you using?

Presuming you’ve seen the Adafruit setup guide, it might be worth asking Adafruit directly- either on their discord server (https://discord.gg/adafruit) or on their own forums.

#6

Okay, thanks for the help all. Now only 5m off - maybe the rain was skewing the figures a bit. I am using the Adafruit Python library. I have already coded a quick script to use an API to get the QNH and it works a treat. No chance of it being completely accurate as weather stations seem to all round their pressure readings to the nearing whole millibar. I will ask on the Adafruit Forums to find out how to optimise accuracy.

Thanks,
Louis

Edit - it turns out the API I am using gives double figures, oops

#7

The QNH is what airline pilots use to set thier altimeter in the plan so it “should be” super accurate.
What you get in weather forecasts from a radio station not so much.

I have a couple of weather clocks using a BME680 and Raspberry Pi A+. I’m only interested if the pressure is low or high etc. I don’t bother correcting for sea level and round off my readings to whole numbers. My house is about 90 feet above sea level and the dog park I take my portable to is maybe 20 feet above sea level. Not enough difference for me to worry about for what I use my weather clocks for. If I was wanting accurate altitude readings like you are, it would be a different story.