Adahrs compass calibration

[grusa]

I have had four attempts to recalibrate the magnetic compass in the sky view. We have two screens, two Adahrs in a ctls. The Adahrs are mounted in the wings well away from any ferrous metal, and are correctly aligned and leveled.
The best result I can obtain is (actual / 200 / 201) (the true bearings obtained accurately by hand held compass well behind the aircraft and good to <1degree).
E 91 92
S 169 149
W 271 269
N 21 12
The gps track and heading are accurate to 1 degree and agree with the calibrated card compass headings.
What do I do next?

 

[dynonsupport]

The system calibrates both ADAHRS at once (but only uses one at a time), so you might switch to the other manually to see how they compare. I don't have a unit in front of me to give you the key presses, but it's in the in-flight setup menu for sure, and I think the regular setup menu too.

 

[grusa]

Yes, I understand that both adahrs are calibrated at once. Sadly it makes no difference which one we use - both are accurate E-W and approx 12degrees off N-S.

 

[dynonsupport]

I think (but am not certain - I'm not posting this from the office) that the magnetic inclination and intensity numbers are displayed on the calibration screen. Are they in your case? What are those numbers? And where are you in the world?

 

[grusa]

My location is Pattaya, Thailand:-
N12.900
E100.934
Mag Intensity 42177 nT
Mag Inclination 12.3deg
Mag Variation 0.6 deg
Does this help any?

 

[dynonsupport]

So the mag intensity and inclination look right. Then next thing I'd look at are ferrous metal and other electrical interferences that might be causing issues (I realize you think that you don't have an issue here). To test this - is there any way you can get a physical compass in the area of the ADAHRSs to see if it deflects similarly when in one of the "bad" directions?

 

[dynonsupport]

Also, does the calibration process seemingly complete successfully?

 

[grusa]

Compass - done. There is no detectable magnetic influence in the area of either of the Adahrs. The compass used is a Suunto marine bearing compass, so is known to be accurate.
The system appeared to complete - each direction saved and green, and accepted the update.

 

[dynonsupport]

How close were you able to get to the ADAHRS with the other compass? The occasional customer has found that the mounting hardware they've used to attach the ADAHRS to the ariframe has contained magnetized steel bits (usually bolts and other mounting hardware) that have very local effects.

 

[grusa]

The compass was in contact with the wing, immediately below the adahrs, so about 3". The fixing bolts are stainless and do not appear to be magnetised, certainly they are not attracted to a magnet. The only other metal parts nearby are the pneumatic fittings - brass, the aileron bellcrank and associated bearings, etc. - not much I can do about those, about 10" away, and tie down rings - stainless, non magnetic, but I will try removing them, and whatever they screw into embedded in the wing structure.

 

[mmarien]

I had a lot of trouble finding the interference with mine. It was nearly undetectable even when I placed a compass right on the source of the interference. I think the ADAHRS is very sensitive to any magnetic interference.

http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1302424679/10#10

 

[jakej]

The compass was in contact with the wing, immediately below the adahrs, so about 3". The fixing bolts are stainless and do not appear to be magnetised, certainly they are not attracted to a magnet. The only other metal parts nearby are the pneumatic fittings - brass, the aileron bellcrank and associated bearings, etc. - not much I can do about those, about 10" away, and tie down rings - stainless, non magnetic, but I will try removing them, and whatever they screw into embedded in the wing structure.

FWIW- If Im unable to get an ADAHRS more than 15" from my preferred initial location then it goes to a second option - never had a location that was a problem.  Installed  15 + so far    Keep at it, the results will be worth it & get rid of the stainless steel screws, I use brass or plastic/nylon types.

HTH

Jake J

 

[dabear]

I had zero problem getting the ADHARS set up once in the airplane.  If you are absolutely sure that you don't have magnetic interfence, I have to ask, how are the two installed? 
Are they next to each other (even in horizontal plane). 

You might try staggering them side to side and front to back.  Mine are installed off set like that.

 

[grusa]

They are installed, one in each wing, about 4' outboard.

 

[dynonsupport]

They are installed, one in each wing, about 4' outboard.

We're aware of an issue in dual ADAHRS installations such as yours if one ADAHRS has an issue, but the other one doesn't have an issue, BOTH will fail the calibration process.

The workaround / troubleshooting for that issue is to temporarily disconnect one of the ADAHRS, then try the calibration.

If you successfully calibrate one ADAHRS, then try swapping the successfully calibrated unit to the other position and doing another magnetic calibration (putting known good hardware in a suspect environment).

If after the isolation and swapping, the problem seems confined to one specific ADAHRS unit, then please contact Dynon Tech Support to arrange for a replacement ADAHRS.

 

[jc2da]

I am having a difficult time calibrating my compass as well. This is with a single ADAHRS unit. I have tried more than half a dozen times, each time varying the location of the compass rose, replacing brass hardware, etc. etc. Using a small magnetic compass in my installation area doesnt show anything unusual. Not sure what else i can do to resolve this issue.

Each time, I line up on the compass rose, and hit acquire. When after the last ordinal is calculated, I get the below screen and message: calibration failed.

here is a screenshot:

 

[dynonsupport]

Give our support team a call at 425-402-0433

 

[jc2da]

Yea! Issue resolved. ADAHRS unit was bad. I hope Dynon figures out what happened. A replacement unit fixed all my issues. I finally now have believable wind information. Also, on the defective unit the compass was getting worse and worse. When I first flew, synthetic vision showed me lined up perfectly on the runway centerline. 2 months and some dozen of attempts to calibrate later, SV was showing me lined up some 45 degrees off the centerline.

 

[skydancer]

I calibrated my ADAHARS this weekend, after the first attemp, East direction was off for 10 degree (read 100), West was off for 15 degree (read 285), both North and South were right on.

Then I recalibrated again, I did East first, then West, then North, then South. All four directions came out to be within 1 degree from the Airport compass rose.

Hope this helps.