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Old Mar 09, 2010, 06:30 PM
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Originally Posted by billpa View Post
Teej, the sensor needs to be in 3rd party mode for the data to be meaningful. In "raw" mode, the data format is proprietary and needs lots of postprocessing. There's no advantage to using that mode, and the data will look like random numbers.
I understand where you're coming from...and perhaps this means there's something wrong with my Altimeter....or maybe I'm just asking it to deliver
something it's not capable of. I'd love to hear your thoughts.

The doc claims accuracy to within 1 meter. I generally see swings of 2-3 meters sitting inside, on a desk, with no air moving.

With my ET logger, and the sensor in non-3rd-party mode of course, moving around my house with a difference between top height (me standing on main level holding sensor at arm's length...down to basement floor) of about 18 feet....the ET software, or the device in 3rd party mode, give me numbers spanning over 30 feet.

When I take it out of 3rd party mode and log just the first 2 numbers retrieved, I get integers of around 11,500. The variance between the 2 "extremes" above is down to about 23-24 feet...and tracks the actual height much more smoothly (when subtracted from an arbitrary value to account for the fact that it's measuring pressure rather than altitude).

ie I might see 11522 on my desk, 11518 extended up at arm's length, and 11535 on the basement floor, for example. I can almost count the steps on the stairs.

Here's an example with the ET logger software (and obviously not 3rd party mode)... For this, I powered up on my desk. Waited ~ 10 seconds, then put it up on a bookshelf for about 10 seconds (that's nearly 2m above my desk.)

I then lowered it to waist level and walked to my staircase and descended. Waited 20-30 seconds, then walked back up with the unit at waist height the whole time, placed it back on my desk and disconnected.

I should see it settle out...rise 1-2m for 10 sec, descend back 1-2 down for ~ 20 sec (walking to stairs) then descending ~ 4m (going down stairs)...pausing, then rising 4-5m....and shut off at the same height it was powered on at.

This is what I get (first I did the test in feet, then switched to meters):

Is this the expected accuracy or do I have a defective altimeter? Neither graph properly represents the altitude changes...and seemingly neither registered me walking back up stairs. In both cases I walked back to my desk and unplugged my battery from the logger, and attached the USB cable.
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