Do these barometer readings look correct?

Following on from this discussion, and this one

I have a Pixhawk that was given to me. I was told that the altitude would not hold very well. I gave the guy one of my spares and he loaded it in to his quad and it held altitude quite well.

So now Im trying PX4 for the first time, along with QGC and I'm hoping to be able to check the barometer is working well, before I put it into a frame.

When I have the pixhawk plugged in and powered by USB and sitting still on my bench in my house, the readings I was getting out of the barometer can sometimes vary by about 600mm, over any period of about 30 seconds, so I think i may be using the wrong reading.

I was/am using altitude_local

Can anybody tell me which value or values PX4-pro is using to define the altitude of the copter.


Here are 2 graphs, each showing 2 pixhawks' barometer readings, side by side connected to the same computer. The first is over 5minutes, the second graph is over 30 seconds.

FYI: The lower and upper edges of what appears to be solid lines are actually the points from each of the baro readings, but QGC is reading them as a single line and joining them together as such.



The following graph is taken from dRonin on a Sparky2.0 measuring the baro readings over 5mins


So I guess my questions are:

  1. Do the readings i'm getting out of each pixhawk baro seem correct?
  2. Are there any drivers that need to be checked/updated/replaced?
  3. Over what time scale does PX4-Pro calculate altitude?
  4. I suppose over 30 seconds, a range of 200mm is acceptable?

I have the ability to replace the SMD barometer, so if it is faulty it's not a big issue, I just don't want to do it if I don't have to obviously.


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  • I'm still looking for some insight into how the barometer is actually used in either PX4 or Arducopter.

    I find it concerning that over the space of 5 mins, the altitude slowly drops nearly 1.5m.

    Is this a temperature problem?

    Does the baro need a proper 5V supply instead of just USB?

    Are both these barometers faulty? I find it strange that that would be true, considering these are both legitimate 3DR pixhawks and not a generic clone.

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