Table 4-2.--Gyrocompassing and Calibration Sequence

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

as in digital coarse leveling, all integrators, biases, and

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

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