Tech Note 142 - Calibrate a BME280/680 Pressure Sensor or Barometer

แชร์
ฝัง
  • เผยแพร่เมื่อ 30 ต.ค. 2024

ความคิดเห็น • 47

  • @manishmandal-78
    @manishmandal-78 ปีที่แล้ว +2

    Thanks for the information on METAR. Didn't know that.

  • @santorcuato
    @santorcuato 4 ปีที่แล้ว +3

    Really interesting to use METAR for this purpose. Thank for the idea Dave!

    • @G6EJD
      @G6EJD  4 ปีที่แล้ว +1

      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!

    • @santorcuato
      @santorcuato 4 ปีที่แล้ว +1

      @@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.

  • @wallaceshackleton1889
    @wallaceshackleton1889 3 ปีที่แล้ว +3

    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 ;)

  • @ristomatti
    @ristomatti 4 ปีที่แล้ว +4

    Nice an concise, not wasting my time. Thanks for the tip!

  • @h0l0gram
    @h0l0gram 2 ปีที่แล้ว

    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.

  • @Daydreaminginmono
    @Daydreaminginmono 2 ปีที่แล้ว +1

    Really solid video mate, Appreciate that.

  • @williamlucid8907
    @williamlucid8907 4 ปีที่แล้ว +4

    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

    • @G6EJD
      @G6EJD  4 ปีที่แล้ว +1

      Thank you

    • @williamlucid8907
      @williamlucid8907 4 ปีที่แล้ว +1

      @@G6EJD Found reference to the Relative pressure formula: www.meteocercal.info/forum/Thread-How-to-get-the-sea-level-pressure-with-BMP280

  • @fredflintstone1
    @fredflintstone1 4 ปีที่แล้ว +1

    great use of metar, as near Farnborough easy and accurate

  • @TYGAMatt
    @TYGAMatt 4 ปีที่แล้ว

    Most useful information. Thankfully my factory is just a couple of miles from an airport that has metar data. Sweet.

  • @szabonandi
    @szabonandi 4 ปีที่แล้ว +3

    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

    • @G6EJD
      @G6EJD  4 ปีที่แล้ว +2

      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.

    • @szabonandi
      @szabonandi 4 ปีที่แล้ว

      @@G6EJD understood. Thanks for clarification.

  • @jankuhlmann9196
    @jankuhlmann9196 4 ปีที่แล้ว +1

    Very useful Dave, thanks.

  • @tobo5757
    @tobo5757 4 ปีที่แล้ว +1

    Thanks Dave, very usefull.

  • @frankbohnen2347
    @frankbohnen2347 3 ปีที่แล้ว +2

    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

    • @G6EJD
      @G6EJD  3 ปีที่แล้ว +1

      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.

    • @frankbohnen2347
      @frankbohnen2347 3 ปีที่แล้ว

      @@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.

    • @G6EJD
      @G6EJD  3 ปีที่แล้ว +1

      It’s worth noting that the bme280 is calibrated at a nominal sea level of 1013hpa

  • @mr.bianchirider8126
    @mr.bianchirider8126 4 ปีที่แล้ว +1

    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 ?

    • @G6EJD
      @G6EJD  4 ปีที่แล้ว +2

      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.

  • @credovocalensemble8038
    @credovocalensemble8038 3 ปีที่แล้ว +1

    Nice. Are there no APIs that can be used to pull in the local airport QNH?

    • @G6EJD
      @G6EJD  3 ปีที่แล้ว +1

      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.

    • @IrishHopper
      @IrishHopper 3 ปีที่แล้ว

      @@G6EJD Great news. A short-TAF would also be useful for us aviators :-)

    • @G6EJD
      @G6EJD  3 ปีที่แล้ว

      @@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.

  • @r1273m
    @r1273m 4 ปีที่แล้ว +1

    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

    • @santorcuato
      @santorcuato 4 ปีที่แล้ว

      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

    • @G6EJD
      @G6EJD  4 ปีที่แล้ว +1

      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!

  • @kaid.8932
    @kaid.8932 3 ปีที่แล้ว

    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

    • @G6EJD
      @G6EJD  3 ปีที่แล้ว +1

      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.

    • @kaid.8932
      @kaid.8932 3 ปีที่แล้ว

      @@G6EJD Just bought myself BME280 and BMP388 and will give it try and look if there are differences in accuracy.

    • @G6EJD
      @G6EJD  3 ปีที่แล้ว

      You will find with the air pressure that it’s feasible to measure altitude differences down to 0.1M resolution they are impressive devices

  • @robertrade
    @robertrade 3 ปีที่แล้ว +1

    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.

    • @G6EJD
      @G6EJD  3 ปีที่แล้ว +1

      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.

    • @robertrade
      @robertrade 3 ปีที่แล้ว

      @@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.

    • @G6EJD
      @G6EJD  3 ปีที่แล้ว +1

      @@robertrade I see what you mean, so ideally it would need a seasons switch to be added based on date ranges.

  • @s.husain6125
    @s.husain6125 4 ปีที่แล้ว

    Wow great David sir please also make video on temperature calibration

    • @G6EJD
      @G6EJD  4 ปีที่แล้ว +1

      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.

  • @viveka801
    @viveka801 2 ปีที่แล้ว

    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?

    • @G6EJD
      @G6EJD  2 ปีที่แล้ว

      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.

  • @fleetinglife2984
    @fleetinglife2984 4 ปีที่แล้ว

    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。

    • @G6EJD
      @G6EJD  4 ปีที่แล้ว +1

      You need to use the hypsometric formula that includes air temperature to get a very accurate value, or just use google earth!

    • @imadeddinerabia9541
      @imadeddinerabia9541 ปีที่แล้ว

      ​​@@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)

    • @G6EJD
      @G6EJD  ปีที่แล้ว

      @@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.