compass fluctuations

[GCDXT]

I've got EFIS D10A (v2.17.00) and EDC-10A (v1.05.00) in my RV9.  The EDC is in the wing tip.  The set up originally worked fine and was steady but now I seem to have some fluctuating compass readings.  I've re-calibrated twice but with no real improvement.  After re-calibration the headings are up to 30 deg off.  The EFIS reads the EDC but there seems  to be some magnetic effects near the panel (when I close the canopy).   I assume the EDC should not be effected by canopy movement and that the EFIS should be getting info only from the EDC, the wet compass is effected by cockpit closure but not as much as the D10A.  In summary 3 symptoms:  Wandering readings, not accurately calibrated, seems to be influenced by effects remote from EDC.

Any ideas?
best regards
Tom

 

[dynonsupport]

Wave a magnet around both the EFIS and the EDC. The one that responds with a heading deflection is the set of sensors that are active. I suspect that you'll get movement around the EFIS but not the EDC. If this is the case, the EDC is not connected. In this case, you should first check out the wiring between the EFIS and the EDC.

 

[GCDXT]

I've performed the magnet test and the signals are definitely coming from the EDC. The magnet has no effect when waved at the EFIS. Maybe the canopy closing (its an RV tip up) symptom is just part of the spurious fluctuations. When the EDC is disconnected and the internal compass is displayed (on the EMS) it reads much steadier. I'll see if I can borrow another EDC and see if there is a difference.

Tom

 

[GCDXT]

Using a handheld compass I've determined that the screws and the metal part of the 9 pin connector (it has a plastic shroud) to the EDC have become magenetised. Presumably this has occured because my screw driver has become magnetised. Could this be part of the problem or can the EDC cope with 'non-fluctuating' magnetic fields? I don't want to re-wire with a new connector unless its really necessary.
Tom

 

[meljordan]

I put the EDC in my wing tip originally, but found that location was unacceptable due to the magnetic field caused by the wires for my flashing landing lights and my nav lights. Have you noticed if the fluctuations you are seeing are related to any lighting you may have turned on or not turned on? If you have any wires running near the EDC that are carrying currents, this can cause the EDC to change as the current changes.

Regards,
Mel Jordan

 

[GCDXT]

Although I have wires for strobes / nav lights I have not yet installed these. The aircraft has got about 11hrs now and I first noticed the fluctuations when returning from the paint shop on my last flight. I initially thought the EDC might have been left loose but all appears normal. The compass (EDC) is not steady in the hangar.
regards
Tom

 

[dynonsupport]

The EDC can deal with non-changing fields, but only if they are much smaller than the earth's field. Ferrous but non-magnetized metals are generally fine, but if anything is actually magnetized that could cause a real problem.

Generally hitting metal that has become magnetized will help demagntize it. You may want to try that. Any change in this field will cause your EDC calibration to be totally wrong.

As for it moving in the hangar- is there an elecric motor, transformer, or anything like that in or right outside your hangar on that side? Does a mechanical compass move when set on the wing tip?

 

[GCDXT]

Today I re-connected the 9 pin plug (did not change it as it seems the screws on the alternates are slightly magnetised as well when checking with a hand held compass) and then did MAGCAL a couple of times, well away from all buildings etc. Once I got a 'weak calibration message'. Whilst getting the data on the various headings I noticed that the EDC reading whilst collecting 'EAST' was almost 180 degrees out - is this relevant? The results of my latest MAGCAL are as follows: Heading / EDC during CAL/ EDC after END: 360/320/348, 090/270/000, 180/160/175, 270/235/290. It seems to me that for some reason the EDC has a problem with easterly headings which it cannot correct for. The mechanical compass seems fine.
brgds
Tom

 

[dynonsupport]

Tom,

Just checking: Do you have the 9 pin connector facing the front of the plane so the long direction of the box is parallel with the wings? Do you have the box mounted so that the flanges on the box are on the bottom? Is it tilted at the same angle as the EFIS?

Also, when you say it originally worked fine, do you mean you had it installed and calibrated and then it just stopped working one day? Was this associated with a software update or anything else you can think of?

 

[GCDXT]

The socket faces fwd, the flang is on the bottom. It all worked fine for about 10hrs (also OK after software update). I had the aircraft painted and on the return flt it seemed OK intitially (hdg 170) but after about 30 mins when turning onto an easterly heading I noticed the tape moving erratically. As I was almost at destination I did not study it too much but assumed that the EDC was loose in the tip as a result of work during painting. On the ground I found the EDC was secure and commenced the above thread.
brgds
Tom