Securing the Gyrocompass

Working with the sensing circuit is a second relay.

latitudes 75 and 90 near the poles. In these latitudes,

It operates to indicate when the batteries are being used

horizontal earth rate becomes very low and results in an

as the supply.

excessive compass period and poor azimuth accuracy.

In the high latitude mode of operation, damping is

In figure 4-40, the inverter portion depicts the

increased to a level just below the fast-settle mode of

components of the inverter that receive their power from

operation. The high latitude mode of operation is used

the battery charger.

between 75 and 86 latitudes and the directional gyro

Input power to the shunt regulator is regulated to 6.8

mode of operation is used when a ship is navigating

volts, controlling a 36-volt output that is transmitted to

above 86 latitude.

the inverter drivers.

High latitude mode of compass operation should

be used between 75 and 87 latitudes. Operation in

The frequency reference, containing its own

normal mode is generally undesirable in these

separate power source, employs highly stable

latitudes because horizontal earth rate (proportional to

components to yield an 800-Hz output. In essence, it

the cosine of latitude) becomes very low at high latitudes

consists of a voltage regulator, a relaxation oscillator,

and results in an excessive compass period and poor

and a pulse amplifier.

azimuth accuracy. In this operation, a larger signal is

The 800-Hz output of the frequency reference

applied to the gyro leveling torque amplifier and

circuit is used to control a master multivibrator

damping is increased to a level just below the fast-settle

(inverter). The action of the symmetrical multivibrator,

mode.

while running at 400-Hz, is to control three slave

multivibrators.

In the directional gyro mode, the compass takes on

many of the characteristics of a free gyroscope.

The four multivibrators are divided into two driver

inverters (one master and one slave) and two power

It has been shown in previous sections how the

inverters (stage A and stage B). The yielded output is a

degree of tilt of the meridian gyro controls azimuth

2-phase, approximately 86-volt, 400-Hz sine wave.

accuracy of the Mk 19 Mod 3B gyrocompass

Considerable filtering is employed, with both the

equipment. (Tilt controls torque about the tilt axis that

amplitude and the phase being controlled. The 2-phase

controls precession toward the meridian.) At very high

voltage is then sent to a Scott "T" transformer network

latitudes the degree of tilt becomes very small because

from which it emerges as 3-phase, 115-volt, 400-Hz

horizontal earth rate, which is proportional to the cosine

voltage to the output circuit.

of the latitude angle, becomes very small. The torque

Incorporated in the output circuitry is a radio noise

about the tilt axis that causes azimuth precession of the

filter and the primary of the voltage regulation control

compass toward the meridian, therefore, is very small,

to the driver multi vibrators.

resulting in weak azimuth control and consequently

long periods and poor accuracy.

Further control is also exerted by a transformer in

the power inverter output that reflects any overcurrent

The torques required to correct the meridian gyro

signal below the maximum capabilities of the individual

for east-west speeds are proportional to east-west speed

multivibrators.

in knots, multiplied by the tangent of the latitude angle.

The large amount of energy stored in the out-

The tangent function is equal to zero at the equator (0)

put circuit filters requires a clipper circuit to be

and equal to infinity at the pole (90). The torques

employed due to sudden quenching of voltage or

required to correct for east-west speed at, or within 3

removal of load.

or 4 of, of pole approach infinity and are, therefore,

impossibly high.

There has also been some changes in components

and circuitry to raise the ambient operating temperature

When Mk 19 Mod 3B gyrocompass equipment is

of the system from 110F to 149F.

operating in the directional gyro mode, it functions

The Mk 19 Mod 3B system also has two additional

much the same as a simple gyroscope. The polar

modes of operation not found in the Mk 19 Mod 3A

coordinate system used in the other three modes of

system. These two additional modes of operation, or

operation cannot be used in the directional gyro mode

auxiliary modes as they are called, are the high latitude

because the compass, instead of pointing north, will

mode and the directional gyro (DG) mode. These

point in a direction parallel to the meridian at point of

auxiliary modes of operation are used between

entry into the directional gyro mode.

4-39