DESIGNER’S HANDBOOK 4189350049C EN
Page 177 of 206
In some case the same NMEA sentence can contain different data types, it can for example be MWV that is sent
one time with relative wind data and shortly after again but now with true wind data. To see one or the other it can
be useful to be able to freeze the screen. XDR is another example where this function can be quite useful.
In the upper right corner of the screen, you find the total number of received sentences and the error counter that
shows the number of faulty sentences that have been received since the monitor was started. Errors can occur if
the NMEA line is connected and disconnected in a running system, bad connections or it can be caused by a faulty
NMEA transmitter.
If the received data in the first line for a given input port looks strange and has no Count and Time registered, it is
because the sentence format is not in accordance with NMEA standard format. Every faulty string will be registered
as an error. It can be caused by the same bad conditions as mentioned above, but it can also be due to wrong
polarisation of the A and B input terminals. Try to swap the A and B wires around.
Strange looking sentences can also be caused by input data with an incorrect bit rate. The default bit rate on all
NMEA inputs is 4800 bps, but it can be changed via the comport setup located in the INSTALL/NMEA setup menu.
11.16.1.1
NMEA sentence example
The wind sensor is connected to the XDi, but relative wind speed and direction is flashing, and the data lost pop-up
is shown on the indicator.
Enter the service menu and select the NMEA monitor to see the received NMEA sentences.
The NMEA monitor shows:
This means that 25 sentences are received since you started the monitor, and the MWV wind data sentence is
received (RX) every 1.0 second from COM port 2.2 (Slot 2, NMEA input RX2).
$
is the start sign of the NMEA sentence
WI
is the talker ID for a weather system.
MWV
is the weather sentence
70
is the wind angle (wind angle can be from 0 to 359 degrees)
R
means that it is relative wind, it can also be T=true wind
14.6
is the wind speed
N
means that wind speed is in knots (other valid units: K=km/h and M=m/s)
V
is the data status flag, V = data is invalid and A = data is valid.
*2E
is the termination and checksum
Note: You can find the standardised NMEA sentences with explanation of the actual sentence content in the
IEC 61162-1 standard or in the NMEA0183 standard.
25 1.0 2.2 RX $WIMWV,70,R,14.6,N,V*2E