The north-seeking element of the NAVIGAT 2100 gyrocompass system is the fiber-optic sensor unit. It is a solid-state design with no moving parts. Designed in strapdown technology, it is attached directly to the vessel, eliminating the use of a gimbal system. The sensor unit contains three fiber-optic rate sensors, a dual-axis electrolytic level sensor, a navigation processor unit and a power supply.
The three rate gyros are arranged orthogonally and measure thus the rotation of the sensor unit about a vessel's x, y and z axes. The electrolytic level sensor measures the inclination of the x and y axes relative to the horizontal.
This configuration is known as an "analytical platform." On the basis of the vessel-referenced sensor data and the external speed and position (lat. and lon.) inputs, the navigation processor uses a complex Kalman filter algorithm to determine the direction of true north.
To initialize the Kalman filter parameters, a so-called alignment procedure is carried out when the system is energized. During the alignment procedure and during normal operation, the system continually and simultaneously performs two essential tasks which make it north seeking, namely horizontal alignment and north orientation. After power-up the system establishes a virtual plane, the so-called inertial plane.
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The Inertial Plane |
The Virtual Horizontal Plane |
The Virtual Horizontal Plane
Aligned with North |
By evaluating the data from the electrolytic level sensor, the system is able to determine by which magnitude the virtual plane would have to be inclined to position it horizontal at the vessel's location.
By transforming the data from the rate sensors, the system is also able to determine how the movement of the vessel and the earth's rotation act on the virtual horizontal plane.
By processing the data from the exernal speed and position inputs, the system is able to calculate the component of the earth's rotation which acts on the virtual horizontal plane and in so doing determines the rate at which the horizontal plane has to be inclined to maintain it in a position horizontal to the earth's rotating surface.
