Figure 4-47.--Inertial measuring unit exploded view.

FUNCTIONAL DESCRIPTION

INERTIAL MEASURING UNIT

The primary function of the stabilized gyrocompass

The IMU (fig. 4-47) is installed in a special

set is to produce precision analog dual-speed roll, pitch,

precision IMU alignment rack located in the bottom of

and heading signals for use by the ship's equipment. The

the electrical equipment cabinet, behind an access cover.

outputs are available in all modes during normal

Access to the IMU is gained by removing the access

operation and battery backup. When operating on

cover. The IMU contains the gimbal assembly, the

inverter produced single-phase power, only vital

electronics necessary to maintain the gimbal assembly,

heading and its synchro reference are available.

and associated electronics necessary to interface with

For the stabilized gyrocompass to operate, it

the control, computing, and processing functions of the

requires certain electrical inputs from the ship. These

control power supply. The IMU also contains BITE

inputs are 115-volt ac, 400-Hz, single-phase synchro

circuitry and indicators and houses temperature

excitation; 115-volt ac, 400-Hz, 3-phase primary power;

controlling electronics.

underwater log data with reference voltage; and 24-volts

dc provided internally by the battery set and used during

the loss of 3-phase input power.

SIGNAL DEVELOPMENT

The roll, pitch, and heading (in some publications

referred to as azimuth) located in the IMU gimbal are

excited by 26 volts, 4.8 kHz when the gimbal is caged,

or by 26 volts, 400 Hz during normal operation. Both

resolver excitation levels are provided by the

servoamplifier. Each resolver has two outputs, which

represent the sine and cosine of the angular

displacement of its respective rotor shaft. These outputs

are sent back to the servoamplifier when the gimbal is

caged. When the gimbal is uncaged, during normal

operation, the outputs are sent to the resolver

preamplifier.

The roll and pitch sine and cosine signals from the

resolver preamplifier are amplified, buffered, and

converted to standard three-wire format by the synchro

signal amplifier. The data leaves the synchro signal

amplifier as S1, S2, and S3 synchro data.

The heading sine and cosine signals from the

resolver preamplifier are converted to true heading sine

and cosine signals in the 1X and 36X true heading

converters before being sent to the synchro signal

amplifier and the analog/digital (A/D) multiplexer. The

true heading sine and cosine data, like the roll and pitch

data, are amplified, buffered, and converted to standard

three-wire synchro data in the synchro signal amplifier.

True heading data is subsequently sent out as S1, S2,

and S3 synchro data.

The roll, pitch, and heading sine and cosine signals

from the resolver preamplifier and the true heading sine

and cosine signals from the true heading converter are

also sent to the A/D multiplexer. The A/D multiplexer

Figure 4-47.--Inertial measuring unit exploded view.

sends these analog signals to the A/D converter, where

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