The MK 37 VT Digital Gyrocompass Equipment contains an electromechanical gyrocompass with three precision gimbals. The gimbals and additional electromechanical components compensate for the earth's rotation and gravity while taking advantage of gyroscopic inertial properties. The result is a gyrocompass that automatically seeks and aligns itself with meridian pointing toward true north. A gyrosphere containing a gyroscope rotor is immersed in silicone fluid and is designed and adjusted to have neutral buoyancy.

This feature is a distinct advantage in that:

• The weight of the gyrosphere is removed from the sensitive axis bearings.
• The gyrosphere and bearings are protected from excessive shock loads.
• Sensitivity to shifts of the center of mass of the gyrosphere relative to the sensitive axis is eliminated, thereby providing improved accuracy.
• The effects of accelerations are minimized because the center of mass of the gyrosphere and the center of buoyancy are coincident.

The system's application software compensates for the effects of the ship's varying speed and local latitude. A servo followup system works with the azimuth axis to keep the yoke aligned with the gyrosphere as the vessel turns. The servo system also provides uncorrected heading data to the Electronics Control Unit. The system doesn't require heaters due to the low viscosity of the suspension and ballistic fluids.

Display Assembly
The Display Assembly is the operator's primary user interface to the system and contains the controls and indicators used during the normal operation of the gyrocompass equipment. The Display Assembly contains an LCD, LED indicator lights and displays, and switches.
The operator refers to the indicator lights to determine the current operating mode. Possible modes are ACTIVE, STANDBY, SETTLE, PRIMARY, or SECONDARY. A separate indicator light informs the operator of FAULT detection. The operator has front panel access to ten switches on the Display Assembly. The switches enable the operator to select operating modes, mute audible alarms, adjust the intensity of the indicator lights, adjust the Display Assembly's back panel lighting, scroll
through menu options, and enter data.

The LCD provides the operator with menu options and fault messages. The LED displays provide the operator:

• Current heading to the nearest tenth of a degree.
• Current speed to the nearest knot.
• Local latitude to the nearest degree. Horizontal indicator light indicates if the latitude is North or South.

Electronics Control Unit
The Electronics Control Unit contains a microcomputer and other control circuitry needed to operate the Master Compass and the Display Assembly. It also contains the circuit boards that drive the step repeaters.Connections are provided on the motherboard for up to eight 24 VDC step repeaters. Included in the Electronics Control
Unit is software that compensates for errors due to the effect of the vessel's latitude and speed. The corrected heading data output is provided in both serial and step data format. An analog rate-of-turn output is also provided by the Electronics Control Unit.

Dual Compass Configuration
This configuration allows two complete MK 37 VT gyrocompass systems to be installed on the ship. The gyrocompass systems are designated as primary and secondary. The primary and secondary gyrocompass systems share a common output bus. However, the system that is currently operating in the active mode maintains control of the output bus. Only the outputs from the active gyrocompass system are available to external devices.