OMC-131 True wind display
Users’ manual
V1.14
Page 12
TDC-April-2017
2.2.11 Serial input Port 4: GPS (GGA & VTG)
Input port is always used for input of GPS information. This can be information of ships speed and
heading calculated by the GPS (true speed and heading) and position of ship (longitude and
latitude)
Expected messages are , VTG (Course and ground speed) and the GGA message. (see page 9)
$GPVTG,xxx.x,T,xxx.x,M,xx.x,N,xx.x,K*hh <CR><LF>
T
= Course degrees true
M
= Course degrees magnetic
N
= Speed over ground in knots
K
= Speed over ground in km/h
hh
= checksum
$GPGGA,hhmmss,llll.ll,a,yyyy.yy,a,b,cc,dd.d,xx.x,M,xx.x,M,gg.g,kkkk*hh<CR><LF>
llll.ll
= GPS latitude North or South a = N/S
yyyy.yy
= GPS longitude East or West a = E/W
b
= GPS quality indicator 0 = GPS invalid, 1 = GPS fix, 2 = DGPS fix
cc
= Number of GPS satellites being use
dd.d
= Horizontal dilution of precision
M
= Antenna height relative to main sea level
M
= Geoidal separation units in meters
gg.g
= Age of differential GPS data
kkkk
= Differential reference station ID
hh
= Checksum
"b" is used to select at which speed the OMC-131 starts to use the gyro and log information to
calculate the true wind speed and direction.
When the quality indicator gives "0" unit switches immediately to gyro and log.
When the quality indicator gives "1" unit goes below 3 knot speed to gyro and log.
When the quality indicator gives "2" unit goes below 1 knot speed to gyro and log.
Output port is used to transmit true and relative wind information in the NMEA-183 format.
Output message,
$IIMWV,xxx,T,x.x,M,A*cscs Theoretical wind message
$IIMWV,xxx,R,x.x,M,A*cscs Relative wind message
$IIMWV,xxx,M,x.x,M,A*cscs True wind message (used for True wind displays, like OMC-138)
"M" means meters per second
"A" means message valid "V" means message invalid
