differing heading on two NN3D units

[sailor11767]

I have an installation of two MFD8 chartplotters. My problem is complicated by several variables over the winter.

During the winter, I moved and changed most of the 0183 connections. Changed between plotters and different data ports. I don't think that has an impact in my problem but not sure.

I also discovered last month that my 330B GPS receiver expired (GPS Rollover) in January, and I replaced it with a unit that has a combined 10 Hertz heading sensor. My previous heading sensor came in on 0183. While I have zero prior experience with this combination of pieces, the new GPS and heading sensor appears to be working well and providing consistent data.

My problem is that my two MFD8 units show heading readings that differ by about 40°. As part of my troubleshooting, I have physically turned off all other data sources (all 0183) And when I pulled the fuse on the N2K network, both displays lost their heading data. So I am pretty sure they are working on the same (N2K) data stream.

Curiously, the radar overlays are both correct. And since radar overlay requires a compass heading, that is peculiar.

I did briefly consider variation as the problem, with one reading true and one reading magnetic; however, the variation here is 10° and both are set for magnetic.

I'm stumped!

 

[sailor11767]

Two additional data points.

TheN2K heading sensor came in at the helm and the 0183 heading sensor comes in at the nav station. I have just re-enabled the 0183 heading sensor and set it as global data source. Both units now display the same heading.

Another issue that may or may not be related, is that when using the N2K heading sensor the heading changed at 10 HZ and the display was constantly shifting. On the 0183 heading sensor, the display is much more stable -- even though it is also 10 Hz.

 

[Johnny Electron]

My first thought is you have an issue with MAG VAR. There are some low cost GPS sensors out there that don't put out MAG VAR (won't name the G brand) and it can cause issues if you don't have another good source of Mag Var. I would recommend drawing out the system with your connections and opening a support case so the techs can review it. I would recommend you check that both displays have the same software revision, preferably the newest (2.13).