Tech Note 142 - Calibrate a BME280/680 Pressure Sensor or Barometer
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- เผยแพร่เมื่อ 10 มิ.ย. 2024
- Ensure your pressure sensor or barometer readings are correct by using a METAR station, these are highly accurate weather stations provided for aircraft altimeter adjustments. There are 1000's around the world for nearly all known locations.
Example of stations: cnrfc.noaa.gov/metar.php - วิทยาศาสตร์และเทคโนโลยี
Thanks for the information on METAR. Didn't know that.
Nice an concise, not wasting my time. Thanks for the tip!
Really solid video mate, Appreciate that.
Really interesting to use METAR for this purpose. Thank for the idea Dave!
The ideal is to get an average for a few METAR stations, then adjust for your particular altitude, but it gets too complex to try and explain how to do that!
@@G6EJD Yes, you need to consider the altitude difference to the airport... But for a maker at home that is a good improvement to the calibration / not to calibrate.
One hPa or mB difference in QNH is only 30 feet. The best way is to find your location height above sea level, eg 397 feet and divide it by 30, 13.2 and add this to the pressure reading from the sensor. Good enough for government work.
An interesting video and another insight in the the insatiable curiosity that is a radio amateur. 73s ;)
Very useful Dave, thanks.
Most useful information. Thankfully my factory is just a couple of miles from an airport that has metar data. Sweet.
great use of metar, as near Farnborough easy and accurate
Thanks Dave, very usefull.
The METAR published pressure "QNH", is the pressure if the station would be at sea level. Thus it is calculated/derived from QFE. QFE is the pressure measured at the stations level.
Thank you G6EJD. According to BME280 sensor data sheet; sensor reads absolute Barometric pressure. Altimeter readings use Relative pressure. Found this formula: Relative pressure in hPa = (Absolute Pressure in hPa + (elevation in meters / 8.3)) Absolute Pressure = BME280 reading in hPa Sorry I have lost the source for this formula. Formula is good in most cases. Still needs calibration; however, the difference is much smaller. 73, AB9NQ
Thank you
@@G6EJD Found reference to the Relative pressure formula: www.meteocercal.info/forum/Thread-How-to-get-the-sea-level-pressure-with-BMP280
I started using a ‘fudge factor’ a few years ago when I noticed all three of my BME280’s were reading nearly the same when compared to each other but always off when compared to the pressure from the nearby airport weather station. I was hoping there was a more elegant way of adjusting the pressure, but I guess not. OR maybe my BME’s are correct and the weather station is wrong...... hmmmm..... time to make my own manometer ?
The Bosch sensors are factory calibrated at 1013.25 hpa as that’s a nominal sea level pressure value and so unless you live at sea level they will always be out. There is no offset register on the device, so you have to use an external reference and METAR stations are as good as it gets, you could correct for altitude differences but the difference is margin which is why I prefer to wait for a period of uniform pressure across the region then you can make a good accurate adjustment.
Interesting video. There is a small airport just along the road from me (Shoreham) so I just checked that and compared it with the old aneroid barometer we have. Is it possible to download these values in the same way we download RTC data? Bob
Yes, it is. Try this changing to your airport indicative in case it is not correct:
www.aviationweather.gov/adds/dataserver_current/httpparam?dataSource=metars&requestType=retrieve&format=csv&stationString=EGKA&hoursBeforeNow=0
www.aviationweather.gov/metar/data?ids=EGKA&format=raw&date=&hours=0
Your airport incative seems to be EGKA
Yes you can connect to the aviation server and download a METAR message it’s meant to be easily read by pilots so it’s short, gives temperature dew point and pressure, the latter being prefixed by a Q for QNH see my code example by searching for G6EJD METAR it gives the outline of how to read the data by software, but be aware there’s more to a METAR message than meets the eye!
Wow great David sir please also make video on temperature calibration
The Bosch sensors are factory calibrated fit all 3 parameters, so temperature is calibrated. Pressure is calibrated at sea level so needs to be adjusted/calibrated for altitude.
Hello, the BME280 pressure output is absolute pressure. Your video shows the relative pressure. Is there a function in the library that does the calculation for you or do I've to do that math myself? The formula to do that is (for metric): altitude (in meter) /8 + absolute pressure
Yes that function is in the Adafruit library but it’s of not much use as the resultant altitude varies as air pressure changes, so only accurate the day you run it.
@@G6EJD OK, I found the altitude function. Your right, it looks wired in a chart as your home moves up and down during the day. So, I add the quotient of the formula myself.
It’s worth noting that the bme280 is calibrated at a nominal sea level of 1013hpa
Hi David,
did you consider that the metar air pressure is QNH (Which is ambient air pressure at the station (QFE) calculated down to mean sea level). Which is basically QFE subtracted by the height of the measuring station (in lower altitudes: 30 ft = 1 hPa) .
Best regards,
Kai
30 ft per
Yes, I only choose metar stations that are close and at about the same altitude as my QTH, luckily I have an airfield just 3-miles from my location and at the same height. You make a good point.
@@G6EJD Just bought myself BME280 and BMP388 and will give it try and look if there are differences in accuracy.
You will find with the air pressure that it’s feasible to measure altitude differences down to 0.1M resolution they are impressive devices
Nice. Are there no APIs that can be used to pull in the local airport QNH?
Yes there are at aviation weather I’m publishing a METAR e-paper reader display any day soon so you can see how to do that.
@@G6EJD Great news. A short-TAF would also be useful for us aviators :-)
@@IrishHopper I’m just recording the METAR version now. TAF’s are quite difficult to get hold of but I have no idea why, other than a lot more valuable information in them.
Using METAR for this application is very brilliant. (I'm a pilot)
Plan on adding COLD/Air Condition feature to this system? I understand it requires 2nd relay.
If you mean a thermostat then all that needs to be done for cooling is to reverse the relay co tact’s from using NO Normally Open to the Normally Closed set then as the temperature is met it will stop cooling.
@@G6EJD Thanks for your response. You know, there are 2 separate temperature ranges, one for each cooling and heating.
Think of 4 seasons - winter and summer. Spring/Fall - don't need thermostat to run heat or cool during these off-seasons.
@@robertrade I see what you mean, so ideally it would need a seasons switch to be added based on date ranges.
Meteorlogical pressures are normalized to sea level before published. So if you are not on the same level as the nearby metar station, you may need to compensate the altitude difference as well. en.m.wikipedia.org/wiki/Pressure_altitude
Yes, but most sensors are calibrated at a nominal sea level pressure of 1013hpa, but the important point about a METAR report is it’s not meteorological but based on altitude so an aircraft can set its altimeter, then if a station is nearby or on the same level it alludes calibration.
@@G6EJD understood. Thanks for clarification.
Hi, I have a scenario, that i need to track height of a cube in 3D , when I calibrate it and used .. Then next day again i need to calibrate right?
Yes, air pressure constantly changes, there is no solution other than to take your own reference at the start of the measurement and use a virtual reference point not the earth. Then you will get a delta from 0,0,0 which will be reasonably accurate. This is why aircraft altimeters need to be recalibrated before each flight and during flight and before landing so they know their vertical position.
i use this model ，and i wonder，is there a way to get altitude，i use adaftiut bme lib，but i find in
Example, there is a 1013.25, i can change it, and the
Lib getaltitude function use an fix formula，but the reference hpa i think is vary every day，so i can not use a fix value。
You need to use the hypsometric formula that includes air temperature to get a very accurate value, or just use google earth!
@@G6EJD
I tried it with bme680
Those sensors always use the 1013.25 sea level pressure as a reference, so in a weather condition that chages the sea lvl pressure making it far great/lower than the value, altitude readings also changes even with that formula that includes temperature, so if you stay in one place you should measure the altitude verified by google maps or gps and combine it with other variable parameters for example to get the accurate sea lvl pressure using the formula
the best way i think to get accurate altitude also is using gps module
So using bme sensors only it is impossible to get the accurate altitude only if the sea lvl pressure is accurate to 1013.25mb and thats rare (it is just an average value)
@@imadeddinerabia9541 you can’t calibrate a sensor using altitude as the result will always be an approximation, only a column of mercury will give the correct result and even that needs to be calibrated against some Standard usually held be a national standards institution.