Latitude Set

Reference Speed Selection

azimuth. The alpha angle is held constant and grid

heading, rather than true heading, is sent to the ship's

The software program controls the reference

equipment. Otherwise, the equipment's function is the

same as for the AUTO CAL mode.

speed selection function. The REF SP switch

is positioned by the operator to define to the

SUPPORTING FUNCTIONS

software program the operational mode required. In

the OVRD LOG position, the REF SP switch

provides a ground via the dimming control circuit

The major functions of the stabilized gyrocompass

are supported by several supporting or subordinate

card to energize the OVRD LOG indicator. The

functions. The supporting functions are described in the

REF SP OFF indicator is controlled by the pro-

following paragraphs.

cessor.

The ship's EM log input is changed from synchro

Latitude Set

format to sine and cosine values by the Scott "T"

transformers in the A/D multiplexer transformer. The

The entry of latitude data maybe made during the

EM log sine and cosine signals are selected by the

leveling sequence (except during the north and south

A/D multiplexer and converted to a tangent value, in

gyrocompassing phases) and at anytime the system is

digital format, by the A/D converter. The EM log tangent

NAV ready. The gyrocompass is ready to receive a

latitude entry when the ENTER LAT switch indicator

signal is then applied to the processor. When the

(fig. 4-44) is on. The software program commands

REF SP switch is set to OFF, the processor ignores the

the ENTER LAT switch indicator on when power

EM log inputs and the gyro operates in the free-

is applied and when the position of the MODE switch

inertial state. When the REF SP switch is set to EM

is changed. If the ENTER LAT switch-indicator is not

LOG, the processor tells the software program to

on, entry can be accomplished by pressing the

implement gyro operation, damped by the EM log

ENTER LAT switch indicator ONCE. The gyro

compass will then be able to receive a latitude entry for

velocity information.

1 minute.

The EM log velocity information is monitored for

With the DSPL SEL switch set to LAT and the

reasonableness by the software program. When it

ENTER LAT switch indicator on (fig. 4-44), latitude

determines that the velocity information does not

entry is made by setting the desired latitude

meet the reasonableness test, the processor will

(hemisphere, degrees, and minutes) with the

command the equipment to ignore the velocitly data and

thumbwheel switch, then pressing and releasing the

ENTER LAT switch indicator. The ENTER LAT switch

operate in the free-inertial state. The processor will also

indicator will go off and the selected latitude will be

initiate a reference speed off signal, causing the REF SP,

displayed on the digital display.

OFF indicator to light. The operator can override the

reason- ableness test by setting the REF SP switch to

Data Display

OVRD LOG. In the OVRD LOG position, the processor

disables the velocity monitor and commands the

software program to use the EM log velocity

Several pieces of data are available for display on

the control indicator panel. The data available for

information for damping purposes. The REF SP, OFF

display is latitude, electromagnetic (EM) log, ship's

indicator will go off, and the OVRD LOG indicator will

heading, pitch, roll, and test (table 4-3). The desired data

come on, indicating the equipment is operating in a

is displayed by setting the DSPL SEL switch to the

damped state.

appropriate position. Also, under software control, but

not selectable, are the MODE, ALIGN indicator, and the

When the REF SP switch is set to DOCK, the

MODE, NAV indicator. When the alignment sequence

processor tells the software program to use a zero

is complete, the software program turns the MODE,

reference velocity for damping instead of the EM log

NAV indicator on, and the MODE, ALIGN indicator

off.

velocity input.

4-53