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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

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