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    measuring relative altitude using two BMP390 sensors

    mahivarma
    New Poster

    measuring relative altitude using two BMP390 sensors

    Dear Community

    I have a requirement to measure the relative altitude between two points in space. a module containing BMP390 sensor will be deployed at a certain height. the module will communicate the absolute pressure measured to a handheld device at ground level using wireless communication. the handheld device will have a BMP390 sensor built-in which will measure the barometric pressure at ground level. the handheld device will calculate the relative altitude between the two devices using the difference in pressure reported by the two devices. the absolute accuracy of BMP390 sensor in altitude is approximately 4m whereas the relative accuracy in altitude is approximately 250mm.

    I need my measurement accuracy to be +/-250mm. is there a way I can marry the two sensors and offset the absolute accuracy error?

    there will be multiple devices deployed at the same time. an operator walking on the ground with the handheld device should be able to estimate the height of each of them. this means maintaining a table of calibration offset for each sensor is not very user-friendly.

    the maximum height I need to measure is 30m.

    pls advice me on what I can do to accomplish this?

    Mahi

    5 REPLIES 5
    BSTRobin
    Community Moderator

    Re: measuring relative altitude using two BMP390 sensors

    Hello mahivarma,

    The relative accuracy is for one sensor, not for two sensors.
    For your application, you can calibrate the two sensors first, and then actually test the accuracy of the height difference.

    In addition, even if there is still a drift after the two sensors are calibrated, there is about ±0.16 hPa drift in 12 months, so the two sensors need to be recalibrated after a period of time.

    mahivarma
    New Poster

    Re: measuring relative altitude using two BMP390 sensors

    Thank you BSTRobin for your kind reply.

    I know relative accuracy is for one sensor. my question was how I can get same level of accuracy using two sensors.

    can you elaborate on what do you mean by calibration. are you suggesting me to measure the pressure using both sensors simultaneously at same location and record the difference and then use that difference as a correction factor for future measurements?

    I was wondering whether it will be possible to modify the internal calibration factors of one of the sensors so that they both will report same value if used simultaneously at same location?

    if this is possible then I can do this on a batch of sensors and the measurement accuracy between them can be as good as the relative accuracy of a sensor.

    please advice.

    Regards

    Mahi

    BSTRobin
    Community Moderator

    Re: measuring relative altitude using two BMP390 sensors

    Hello mahivarma,

    Calibration: under the same air pressure environment, read the air pressure value of the sensor and compare it with the value measured by the standard barometer to get an offset. The offset will be subtracted from the data read later.

    After the two sensors are calibrated, you can test the height difference in your application. We haven't done such a test, so we can't determine the accuracy of using two sensors to measure the height difference. You can have a try.

    In addition, even if there is still a drift after the two sensors are calibrated, there is about ±0.16 hPa drift in 12 months, so the two sensors need to be recalibrated after a period of time.

    mahivarma
    New Poster

    Re: measuring relative altitude using two BMP390 sensors

    BstRobin, Thank you for your reply once again.

    my interpretation of your reply is that the offset between the two pressure sensors would remain reasonably constant accross the pressure range. if there is 20hpa difference between the two sensors when exposed to 100kpa, the difference between them when exposed to 50kpa would also be close to 20hpa.

    thank you for this information.

    can you pls also answer the second part of my question

    can I cancel this offset of 20hpa by modifying any of the internal calibration factors such that both sensors will measure same value from that point onwards.

    instead of having an external record of the offset, can I embed it inside one of these sensors.

    Regards

    Mahi

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