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10/18/2020 10:38 pm  #1


Sending PGN data from Expedition onto the NMEA 2000 network

Inspired  by a previous posting on this topic, I am successfully using Expedition to send PGNs via Actisense NGT-1 onto the NMEA2000 network, which I can then view on my Garmin GNX20 displays – the smaller units that don’t allow the custom channels.   This allows me to have Expedition data on these smaller displays as well as having custom data showing on my mast mounted larger GNX120 displays.
 
I am confident that the TWD displayed on the GNX20 is that from Expedition – the unit is set to the Expedition data source and if for example I change the AWAOFFSET in Expedition, then the TWD on the GNX20 changes accordingly - so I think it is not showing an internally calculated value.
 
The problem is that the TWD on the display is always different to the damped TWD number within Expedition, or indeed the same number sent as custom data to my GNX120 displays.  I have checked the “send damped data” box in the Actisense NMEA2000 PGN dialogue box, so I was hoping this meant that the number being sent to the network would be the same damped number that is within the program at any given time.  The problem is that it is not, it seems to be an undamped number.  I could damp it using the facility in the GNX20 display, but the Garmin damping appears to be not the same as Expedition and side by side comparison reveals large differences.
 
So, I suppose my question is, does the “send damped data” option work, as clicking it seems to make little difference to what is shown on the display for TWD.

Thanks in advance for any insight.

 

10/18/2020 10:49 pm  #2


Re: Sending PGN data from Expedition onto the NMEA 2000 network

Yes, it definitely should be the damped value.

However, I have just tested with a GNX 120 and it only seems to display TWD if I also send TWA, TWS, BSP and HDG.

So maybe it always calculates it in the display.

Last edited by Nick (10/18/2020 11:10 pm)

 

10/19/2020 3:08 am  #3


Re: Sending PGN data from Expedition onto the NMEA 2000 network

Ok thank you Nick
I have been discussing this with a very helpful chap from Garmin China - I will let you know how he responds.

     Thread Starter
 

10/20/2020 5:35 pm  #4


Re: Sending PGN data from Expedition onto the NMEA 2000 network

To close this out, Garmin responded to me as follows:

I assume this is the way by design.  PGN130306 does not includes any TRUE wind info, and GNX instrument doesn’t accept PGN128000 yet. So, the true wind info displayed on GNX is calculated internally  by PGN130306(direction & speed of wind) and PGN127250(heading) input from external source.

So I guess it is an internally calculated value.

But what is strange is that TWA is clearly being sent to the instrument as the display value is exactly the same that in Expedition, so the PGN must include True wind info.... 

 

     Thread Starter
 

10/20/2020 8:13 pm  #5


Re: Sending PGN data from Expedition onto the NMEA 2000 network

130306 does include wind direction options, but presumably they have chosen to always do it from twa and hdg ...

128000 is a more recent PGN for leeway.

Last edited by Nick (10/20/2020 8:15 pm)

 

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