Watson Industries, Inc.
GGC-E101 Rev A 08/30/2013
9
Example of the GGS header:
GGC-E101 INITIALIZING
SERIAL NUMBER - 0177
LAST CALIBRATED - 10/12/10
SOFTWARE VERSION - GG01_00A 2010-12-13
COPYRIGHT (C) 1990 THROUGH 2010
WATSON INDUSTRIES, INC.
Normal Operation
During normal operation, the GGC will output highly accurate inertial data for the user to interpret.
This data is transmitted using the RS-232 serial output. The unit also relays GPS messages. The
exact formatting structure is discussed later in the Interface section of this manual.
In normal operation, the GGC takes data from its rate sensors and integrates in a closed loop
system, with the accelerometers as a long-term reference, to generate Bank, Elevation and Heading
data. In most cases, these algorithms provide for very stable and accurate output signals; however,
the user should be aware that exceeding the normal ranges of the sensors would affect accuracy.
The GGC gyros have a maximum rate of 100
°
/s. Care should be taken not to exceed this rate
because the closed loop system will receive inaccurate data. This will result in errors in the angle
output signals. The GPS Velocity data is used to assist in the correction of errors. The internal GPS
receiving unit provides this signal.
The Heading Angle is referenced to the fore-aft alignment of the two GPS antennas using the true
North GPS Heading (the string start label is “G”). If GPS becomes unavailable, relative heading
will be maintained (the string start label is “I”).
While this GGC is "all attitude", the accuracy deteriorates rapidly when its forward direction is
within about 5 degrees of vertical. Operation for any extended period of time in this orientation is
not recommended. If these few operational precautions are observed, the GGC should provide very
accurate data for a wide variety of applications.
Standard RS-232 Digital Output
The standard RS-232 output consists of a five NMEA GPS messages. These strings of decimal
ASCII characters sent asynchronously at regular intervals. Nominally, the string is sent at 9600
baud with eight data bits, one stop bit and no parity. The mating cable for the GGC is included. The
RS-232 signal is referenced to signal ground. The frame rate is 1 frame of five GPS messages per
second. The five GPS messages are GPHDT, GPGGA, GPGLL, GPVTG, GPRMC. The unit is
shipped configured for this output.
Here is an example of the five string frame:
$GPHDT,175.58,T*0C
$GPGGA,175612.00,4451.84239,N,09128.00147,W,2,06,1.1,275.2,M,-33.0,M,6.0,0133*7B
$GPGLL,4451.84239,N,09128.00147,W,175612.00,A,D*78
$GPVTG,186.55,T,187.35,M,0.13,N,0.24,K,D*25
$GPRMC,175612.00,A,4451.84239,N,09128.00147,W,0.13,186.55,081210,0.8,W,D*39
