Hello Arduinites,
I just got my new BMP280 pressure sensor operating, that came with the Arduino sensor kit. It appears to be reading more or less correctly, I am getting readings of avg 101.56 kPa, its a cloudy grey day, latitude 45 deg, eastern North America and I am about 200 feet above MSL. The local weather station the local Baro is 102,8. Wondering if anyone has experience with this unit's accuracy and use. Thanks for any info. Steven Lightfoot
Your sensor is reading absolute pressure at your elevation. Your local weather station's reading is corrected for elevation and is what the pressure would be at sea level.
OK thanks, that makes sense. I did not know that. I worked extensively in gas turbine development, and we always used a local baro to correct our data, but it was actually a real absolute local measurement to the test facility. It never occurred to me that weather data reported locally was never the actual local conditions, but a corrected/normalized reading to some baseline.
I did notice that when I moved to my basement (a drop of maybe ten feet) its readings went from 101.55 ish to 101.57, with higher consistent readings, which isn't much, but is to be expected is measurable and confirms the high sensitivity of this device. Do you have any experience with how baro changes over geographic distance? Would a distance of say 20 km between sensors how a major difference?
20km is more than enough distance to get a major difference given the right weather conditions. You've probably heard the weather folk going on about "you can tell it's going to be windy by how close the isobars are". Isobars are lines of equal pressure, like contour lines on a map. The closer together the isobars are, the less distance you have to move to see a change in pressure even if you maintain the same elevation.
That is because the cheap local weather reporting is what they get from the closest commercial airport. And they ALWAYS use the pressure corrected to sea level because that is what aircraft rely on!
ok thanks. What you say makes sense to me. I am not a weather guy, but I will pay attention now that I have this instrument.
Yes makes sense. Although I am getting data from Weather Network and Environment Canada, so maybe from airport, maybe not. There are scientific weather stations in the area. Could still be corrected. however. I am going to look into this more, here locally.
The correction is a rather complex formula. Look at the library you are using - some of them have a function where you give your elevation and they will do the adjustment.
Yes, good point, I will take a look closer into the Seed/Grove library to see any correction details. I did a cursory search on altitude correction and found that at 107 MASL (my exact elevation confirmed now with topographic mapping), the correction is approx. 13 hPa, so for reading of approx 1015 the SL corrected local value should be about 1028, whish is exactly what I read on the weather website. So its clear the weather reporting uses SL correction, which makes sense, and so my absolute reading from the BMP280 is absolutely correct, within reason. Which is excellent. Thanks for everyone's assistance, and I WILL look closer into that library. Steven Lightfoot
I believe the local weather stations report barometric readings corrected to sea level. You should look for such a conversion and see how close it is to the local barometric reported.
In general I've found the BMP280 to be very accurate, however when you are out in the real world, readings of 10th's of kPa becomes somewhat meaningless as if you move 500 feet the world will have a slightly different temperature.
Thank you, I now have now done a correction to SL and the readings on the hPa level correspond to the local weather service. I will start to do more tests, to better understand the instrument. On the different but related subject, are their commonly used other Arduino style pressure transducers, low cost, that operate for fluids and at higher pressures? I haven't checked but I have to assume yes. Thanks. Steven Lightfoot
An Arduino can read the output of most sensors, although high quality, industrial grade ones often operate at 12-24V, requiring a minimal interface.
Thanks, makes sense. I have a professional background in aerospace control systems, though 20 years ago, so I have a lot of context, though forget many details. I am really excited to have found Arduino, which puts incredible control system power into the hands of kids and DIYers, I am still getting back up to speed on I&C and DAS and trying to figure out where Arduino fits, with respect to professional/industrial systems. I saw one guy on the system, in stories about projects, who managed to control a small gas turbine on his home test bench via Arduino, which was cool.
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