DESIGNER’S HANDBOOK 4189350049C EN
Page 170 of 206
If only HDT was sent, one sentence from each of the two gyro compasses, then XDi would detect 2 usable sources
for both Heading T1 and Heading T2 and ask you to make a manual selection.
In this case we can see that Heading T2 is also using HE HTD, so what you need to do is highlight Heading T2 and
press OK to open it for editing:
In the list you can see all the sources that XDi has detected as
potential sources for “True heading”.
Note: XDi-net is always a possible selection, and it can also be used if you want to disable a NMEA input.
In the actual
case “Heading T2” shall be se
tup to use II HDT, so just highlight this source and press OK to change
the selection.
11.13.3.2.4
Calculated data - HDG cc:
When the magnetic variation, “Mag. Var. 1” parameter is available on NMEA, then XDi is able to calculate the true
heading based on the magnetic heading (from true to magnetic if that is relevant).
In this example true heading can be calculated based on the magnetic heading and the magnetic variation both
available in the HE HDG sentence and it is shown in the selection list as HE HDGcc (cc for calculated).
In the standard library the following is the priority list for the True heading sentence:
HMR, THS, HTD, VHW, HDT, HMRcc, HDGcc, HTDcc, VHWcc
The calculated sentences have the lowest priority, so if the real data is available XDi will prefer to use that, but you
can always change the automatic selection for a given parameter if an alternative is available.
11.13.3.2.5
Finish the installation
The NMEA setup has now been verified and all data needed is available, and all left to do is to press the return
arrow until the heading indicator is shown on the display and starts to present data.
11.13.3.3
Alternative NMEA input configurations for the heading example
Instead of using data from a central control unit the, NMEA data could also be connected directly to 2 NMEA input
ports on the NX2 module and in that case both Gyro 1 and Gyro 2 can use $HEHDT since XDi will differentiate
between the physical input ports as well as the talker ID.
In the example the magnetic heading data is also coming from the heading controller unit with talker ID: HE, but the
magnetic compass could also be connected directly to a NMEA input port on a NX2 module and in that case the
talker ID would most likely be HC ($HCHDG,265.5,…), this will also work find and XDi will automatically detect this
source on a separate input, even if it still was using talker ID HE it will work fine.
When you leave the menu, the NMEA settings will be stored and locked. This means
that only the selected sources will be used by the XDi.
