GYROCOMPASSING AND CALIBRATION.--
of digital coarse leveling is determined by the velocity
A four-step, timed procedure accomplishes the
error signal. When the absolute values of the velocity
gyrocompassing and calibration sequence. This
error signal represent less than 1/2 ft/sec, and 60 seconds
sequence takes approximately 4 hours and must be
have elapsed, digital coarse leveling is complete, and
completed before the gyrocompass is capable of
fine leveling is started.
providing full accuracy outputs. The software program
FINE LEVELING.-- At the start of fine leveling,
estimates latitude if none was entered by the operator.
In either case, latitude information will be updated at the
end of the gyrocompassing and calibration sequence. At
the alpha angle signal are set to zero. Again, completion
the completion of the sequence, the MODE NAV
of the sequence is determined by the velocity error
indicator light will come on, and the MODE ALIGN
signals. When the absolute values of these signals
indicator light will go out, indicating the gyro-
represent less than 1/4 ft/sec and 6 minutes have elapsed,
compassing and calibration sequence is completed.
fine leveling is completed.
Table 4-2 details this sequence.
LEVELING COMPLETION.-- At the end of the
leveling sequence, the software program calculates the
Auto Cal Mode
alpha angle, establishes an initial value for latitude, and
initializes the two direction cosines (pitch and roll
The AUTO CAL mode is used at latitudes below 85°
angles). If a latitude entry was made at the start or during
north or south. The AUTO CAL mode is used at initial
the leveling sequence, that value will be the initial
start-up and should be implemented at least every 90
days during continuous operation to ensure accuracy of
latitude; otherwise, latitude is set to zero degrees.
Table 4-2.--Gyrocompassing and Calibration Sequence