SV-MAG-236 "Losing" Calibration?

[Reaver]

Has anyone seen or heard of the remote magnetometer losing its calibration after a power cycle?

When I do a ground calibration (with or without an in-air calibration afterward) everything seems fine. I can go fly, heading and calculated winds aloft all look good, etc.

However after I shut down the aircraft, the next time I power up it's as if the calibration was never done. Heading is off by 10-30 degrees (depending on heading), and I get claims of 40-kt crosswinds when airports report winds calm.

I've already called Dynon about this and they're putting their heads together as to what it might be, but so far not sure. The SV-MAG-236 is installed aft of the rear baggage wall in a tailwheel Vans RV with no other nearby electronics, the harness is run by itself to the panel, and there are no obvious sources of interference. It's as if the calibration is being stored only in RAM but not saved to permanent storage, although Dynon says that's not possible. Any ideas?

 

[-Bob]

Defective USB memory stick?
Where is the magnetometer calibration information stored?

Flash memory in the Magnetometer?
Flash memory in the Skyview?

 

[swatson999]

Not in a USB stick.

 

[Reaver]

No clue where the data is saved, but I agree it doesn't seem to be on USB. And even if it were, my system has no problem reading charts and writing user logs to the USB drives, so highly unlikely.

Another data point: by entering compass calibration mode while on the ground (on my MFD) then flying, I'm able to keep the screen up in flight. It confirms that the heading shown on my PFD is same as the "CURRENT MAG HEADING ......... WITHOUT CALIBRATION" (bottom line on the compass calibration screen). The GPS ground track seems correct (flying on a calm wind day).

 

[Rhino]

Gremlins. I see a package being sent by you in the near future.

No charge for the fortune telling. It's on the house.

 

[swatson999]

Do this...run the calibrations (ground and air), and before shutting down, download the configuration files. You should see in the USER_CONFIG file an entry for the ADAHRS that looks like this:

ahrs_module={
cfg_count=0
product_id=DYNON_PRODUCT_ID_XENON2
serial_num=2156
alt_adjust=-25.908
hdg_adjust=1.1971
az_offset=-4006
has_pitot_adjust=1
has_aoa_adjust=0
aoa_valid=1
aoa_gain=1.04516
aoa_offset=-0.104657
flap_aoa_cal={
valid=0
gain=1
offset=0
flap_pos=0
}
flap_aoa_cal={
valid=0
gain=1
offset=0
flap_pos=0
}
flap_aoa_cal={
valid=0
gain=1
offset=0
flap_pos=0
}
flap_aoa_cal={
valid=0
gain=1
offset=0
flap_pos=0
}
flap_aoa_cal={
valid=0
gain=1
offset=0
flap_pos=0
}
flap_aoa_cal={
valid=0
gain=1
offset=0
flap_pos=0
}
pitot_adjust_v13=0
aoa_adjust_v13=0
oat_adjust_v13=0
pitch_adjust_v13=0
mag_cal_coeff=16777216
mag_cal_coeff=0
mag_cal_coeff=0
mag_cal_coeff=-590
mag_cal_coeff=0
mag_cal_coeff=16777216
mag_cal_coeff=0
mag_cal_coeff=-2082
mag_cal_coeff=0
mag_cal_coeff=0
mag_cal_coeff=16777216
mag_cal_coeff=456
mag_cal_quality=0
}

Save that file somewhere on your computer, and then on the next start-up, before doing a calibration, download the files again and compare that data. Let us know what you find. (This was an older file that I had on this computer, so yours might look different with later software, but the data should be in there).

 

[Dynon]

. This.

The config files are stored internally. Exporting them to a USB memory stick when you're getting good results and again when you aren't should help tell the story.

The only other thing I can think of - do your displays have the same tail numbers (if you have >1 display)? Displays with the same tail number sync and share configurations, whereas if they aren't the same, you can see some odd behaviors.