SCX20 Compass Variations

[516captain]

I noticed the compass jumps back and forth by about 5 degrees for no clear reason, as if it is using two different sources for direction. It is really noticable when attempting to calibrate to the bow after moving the SCX-20 to a new location on my boat, however I suspected this was happening in the prior location as well.

I confirmed this by tying the boat to the dock and watching over a period of two hours it went back and forth three times between 109 and 114 degrees, the same two directions. Changing sat constellations made no difference. Setting to US only for example. Choosing elevation 30 did not make a difference. The SCX-20 plot is showing many sat's are observable.

 

[jp498]

Perhaps you have a magnetic sensor on the network somewhere? Disconnect it or assign it a higher device instance if it's nmea2k

 

[516captain]

Yes, I do have another sensor on the network. B&G won't automatically select it, but I will give it a try.

 

[516captain]

I assigned higher device instance numbers. The SCX20 stayed at 000; B&G Precision 9 at 002; the ZG100 at 004. I manually recorded heading from each of them over a period of 10 minutes. While the SCX20 drifted back and forth across 6 degrees, the other two were constant, moving at most 1 degree.

My PC based Expedition Software, StripChart feature captured this where the compass reading changed suddenly:

https://photos.app.goo.gl/rMDeUFXE1eiRS5Em7

* The line with the big dip is heading
* The 2nd line with the big dip is Diff Heading vs COG
* The boat is at the dock, in low wind conditions.

I first noticed something is going on, when I was calibrating carefully while motoring. I am a guest marine electronics writer for practical sailor magazine, and before that Panbo and Sail. Could you take a moment to notice if you are experiencing this and let me know.

Thanks!

Dan

 

[Dockhead]

I have the same problem, and it exists even if I have no other compass on the network. Anyone have any clue what this is about? I am assuming my unit is defective and am about to send it in for service.