Gyro Signal Card Assembly

pressurized with dry nitrogen to 700 psig for the high-

Gyro Signal Card Assembly

-pressure accumulator and 38 psig for the low-pressure

The gyro signal card (F106) amplifies and sums the

accumulator.

demodulated pitch and roll synchro signals from the

When hydraulic pressure is applied, the accumula-

ship's gyro with the platform LVDT outputs. It also

tor falls with fluid and the bladder is compressed until

provides offset adjustments to make up for any

the dry nitrogen charge pressure equals that of the

difference in alignment between the ship's gyro and

hydraulic system. In this system, it is 1400 psig. Because

platform. In addition, rate lead signals are derived by

of the bladder compression, the accumulator will absorb

differentiating the ship gyro signals.

pressure fluctuations and prevent hydraulic hammer. If

the system momentarily requires a higher flow than the

Source Light Failure Detector

pump will supply, the accumulator will provide it and

be recharged when the demand has passed.

The source light failure detector is a circuit that

monitors the voltage and current going to the three

Hydraulic Cylinder

source lights. When one or more of the source lamps

fail, the source light failure indicator on the remote panel

The hydraulic cylinders used in this system are

is illuminated

linear actuators. Hydraulic fluid gaited by the servo

valve will push the piston in either direction. The

Power Distribution Circuits

hydraulic pressure exerted by the piston is 1400 psig in

extension and 700 psig in compression. Extreme care

The system requires two power sources from the

must be exercised when working on the system due to

ship 440-volts ac, 60-Hz, 2.7-amp power for the pump

the amount of force available.

and 115-volts ac, 60-HZ, 15-amp power for the rest of

The cylinder is an inherently reliable device requir-

the system. In standby (system circuit breaker on), the

ing little maintenance in normal use. However, the only

system heaters and standby lights are on. When the

required maintenance is cleaning dirt and grit off the

POWER ON push buttons are depressed, the internal

actuator rod and tightening the packing gland nut if a

power supplies are energized except for the 15 volts

leak develops. Do not overtighten the gland nut or the

dc. The 15 volts dc supply is energized after the time

packing will bind on the rod, causing the cylinder to

delay relay has timed out, the hydraulic pump is running,

chatter in operation. If cylinder replacement becomes

and system hydraulic pressure is normal. Then, the

necessary, the defective cylinder must be returned

hydraulic pressure switch is actuated.

through supply charnels for overhaul.

HYDRAULIC COMPONENTS

System low-amplitude vibration, or chatter in some

cases, may be traceable to cylinder internal binding; in

The SGSI system uses hydraulic pressure for

which case the cylinder should be replaced.

motive power. A constant-pressure, variable-delivery

hydraulic pump supplies hydraulic pressure. Pressure

Servo Valve

fluctuations are dampened by accumulators. The fluid

is gaited by servo valves into either side of the hydraulic

Servo valves are commonly used in closed-loop

cylinders. The fluid pressure then causes the cylinders

servo systems. They control the flow of fluid to or from

to move the platform.

the load actuator in proportion to the impact current

signal to the valves' torque motor.

The hydraulic system is sensitive to dirt and other

contaminants. Therefore, care must be used when

Hydraulic Pump

adding fluid or opening any part of the hydraulic system.

Refer to the hydraulic pump assembly shown in

The hydraulic pump used in this system is a con-

figure 3-9 when studying the following paragraphs.

stant-pressure, variable-delivery pump. It is similar to a

constant voltage source in which current will vary upon

Hydraulic Accumulator

demand. Referring to figure 3-9, hydraulic fluid is

gravity fed from the reservoir to the pump unit through

The hydraulic accumulators used in this system are

the pump case fill piping to ensure that the pump case is

steel cylinders with internal rubber bladders. Before

full at all times, thus keeping air out of the line. The

motor-driven pump draws fluid through a suction

putting the accumulators in service, the bladders are

3-25