Barometer 0 and 1 off by a foot or two

ArduCopter Copter 4.1
1

I’ve noticed for some time that the two barometers on my Orange Cube are off by a foot or two.

On a short low level hover test flight - the difference appears fairly significant:

differences in barometer
differences in barometer1920×1080 161 KB

Note - I’ve included the rangefinder (Lightware LW20) altitude as a reference in this chart. (the blue line)

On longer range missions at max legal altitude, the difference seems less significant:

differences in barometer 2
differences in barometer 21920×1080 121 KB

Is this something that needs to be addressed - perhaps through some sort of barometer calibration - or should it be ignored?

Here’s the BIN file from the low altitude hover flight:

Many Thanks!

2

Pressure altimeter sources are typically highly precise, but notoriously inaccurate. Even altimeters on IFR rated aircraft have an allowable +/- 75’ tolerance when compared to a known elevation. If your barometers are agreeing within a foot, I’d say you’re getting outstanding data.

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3

Thanks Yuri - very helpful.

You’re absolutely right about the altimeter accuracy requirement for civil aviation. (VFR and IFR if I remember correctly)

But being new to sUAS and Cube flight controllers, I had no idea what the acceptable allowances might be.

I don’t remember seeing anything in the docs about checking barometers in the tuning guide. I’m guessing that if EKF is synthesizing an altitude from available inputs, consistency matters more than accuracy - especially when operating in “relative” reference to terrain.

I’ll make a post to the folks at Cube Pilot and ask them how closely to expect the barometer alignment - and when to be alert for trouble.

In the mean time, I’ll try to remember checking this in the future when I implement a new flight controller.

4

I think this chart is really acceptable.
You can ignore it unless you want a very precise altitude :slight_smile:

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