Garmin 500, Negative elevation reading.

RHT
RHT Posts: 34
edited January 2011 in Workshop
Sorry if this is in the wrong forum. Has anyone else experienced issues with the elevation readings on a Garmin 500. I know you can manually set an elevation from a known datum, but this was being done with some degree of accuracy via gps up until I updated the software. Now I’m only getting negative readings. Yesterday at sea level I was at a recorded elevation of -120

Does anyone know if there is a 'fix' or do I have a faulty head unit?

Comments

  • sungod
    sungod Posts: 17,542
    garmin's elevation data is notoriously bad on the 705, probably the same on the 500

    both use a barometric sensor to allow detection of small changes, but don't seem to use gps data to adjust for true altitude

    it's not a complex algorithm, but garmin either gets it wrong or just doesn't bother

    at least with the 705, even if you use a stored reference point to set altitude at start, it will soon drift far away from this, so the feature is of little use

    firmware version can also make a difference

    if you look in the garmin 500 forum, you'll find posts on the subject

    https://forums.garmin.com/showthread.php?t=15543
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  • Just had my 705 replaced for this fault, Garmin sent a brand-new unit. :) Top job Garmin.
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  • Garz
    Garz Posts: 1,155
    You could enable the 'elevation corrections' in the software?
  • moonshine
    moonshine Posts: 1,022
    BArometric pressure at the moment is sky high - 1040mb or thereabouts, that may explain some spurious readings if the barometer hasn't been set to take this into account -
  • 2alexcoo
    2alexcoo Posts: 251
    I've noticed some strange readings from my Edge 500 too.

    On today's ride, the starting elevation is shown as zero, even though I've set the known elevation for the start point (about 250 feet). At one point during the ride I got down to about sea level, so it shows the lowest elevation as -250 feet.

    The previous ride was fine, as the elevation graph in Garmin Connect starts at the correct altitude.

    Either way, the total elevation gain seems pretty accurate which is what I'm interested in.
    Alex
  • moonshine
    moonshine Posts: 1,022
    2alexcoo wrote:
    I've noticed some strange readings from my Edge 500 too.

    On today's ride, the starting elevation is shown as zero, even though I've set the known elevation for the start point (about 250 feet). At one point during the ride I got down to about sea level, so it shows the lowest elevation as -250 feet.

    The previous ride was fine, as the elevation graph in Garmin Connect starts at the correct altitude.

    Either way, the total elevation gain seems pretty accurate which is what I'm interested in.

    Precisely... The issue is that you need to keep an altimeter in sync with atmospheric pressure. If you set the altimeter at 200m at an atmospheric pressure of 1003 mb, then turn it off, it thinks it is at 200m. If you then turn it on at a later time , when the atmospheric pressure has changed to say 1040mb the altimeter will register the change in pressure as an elevation change, dispite the fact the altimeter has not changed in physical ekevation. The reason you have a lower elevation shown than you expect is that high atmospheric pressure, the air column above the barometer is more than at low atmospheric pressure, which is equivalent to an elevation drop.
    I have a suunto core wristwatch altimeter / barometer, and in order for the altimeter to he accurate , it needs to be set to a known reference height on a frequent basis. It has a function that allows it to switch automatically between alti / Bari functions on it's own, depending on rate of change of elevation that tries to account for the effects of atmospheric weather systems on pressure based altimeter readings.
  • andrew_s
    andrew_s Posts: 2,511
    The GPS should correct itself from GPS data when you turn it on, but you have to leave it stationary for a while whilst it does so - 10 minutes or so.
    I know the elevation of my house, so I just manually set the height at the start of each ride - it's quicker.
  • Pokerface
    Pokerface Posts: 7,960
    Same thing on my 500 also recently. I just thought I lived below sea level :oops:
  • antfly
    antfly Posts: 3,276
    Mine works very well. Set your home altitude then every time you turn it on wait for it to get a gps signal and then press start and wait for it to say "elevation point found", or something. Then ride. Takes about a minute or less.
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