Page 12 - Electronic Navigation Cyber Book

1.4 STARTING A GYROCOMPASS

As has been previously stated, from start-up a gyrocompass needs time
to settle on the meridian. The time taken depends upon the make, model
and the geographic location of the compass, but in general, it is between
one and several hours. The duration also depends upon whether the gyro
wheel is already rotating or not. If the compass has been switched off, it
will take much longer to bring the compass into use. Inputting the ship's
heading to reduce the initial error factor can reduce the time period. As
an example, the following section considers the start-up procedure for
the Sperry MK37 VT Digital Gyrocompass.

At power-up and prior to entering the settle mode, the system performs
the automatic 'bite' procedure to determine if the equipment is operating
within specified parameters. The CPU also initializes the system
hardware and communication channels. During this procedure, the gyro
wheel is checked for movement. If it is stationary, the system ops for a
cold start, if it is rotating a hot start is programmed. During a cold start, if
no heading data is input to the system when requested, the gyrocompass
selects Automatic.

After an initial period, during which the bite is active, the following
sequence is initiated and the settle indicator lamp will be lit.

• Two bleeps prompt the operator for a heading input. If heading data is
not entered within 5 min, the gyro switches to an 'auto level' process.

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