"Strapdown" induction compass transmitter with compensation for heading errors due to the vertical component of the Earth's magnetic field and due to two cycle error during turns and during climbing and diving maneuvers

Abstract

Abstract The invention relates to an apparatus for compensating a "strapdown" induction compass transmitter to eliminate heading errors during turns and during climbing and diving maneuvers which are due to the vertical component of the Earth's magnetic field and those due to the horizontal component of the Earth's field perpendicular to the axis of tilt. Instabilities and anomalies such as "Northerly Turning Error" which are due to the vertical component of the Earth's magnetic field are thus eliminated or minimized as is two cycle error which is due to the Earth's horizontal field during these same maneuvers. The vertical field roll compensating signal, to compensate for turn induced errors, is made proportional to the product of the Earth's magnetic field M, the sine of the dip angle D, and the sine of the bank or roll angle φ. The vertical field pitch compensating signal, to compensate for errors induced by climbing or diving maneuvers, is made proportional to the product of the sine of the angle φ, the Earth's magnetic field M, and the sine of the dip angle D. The roll compensating signal is combined by summation with the demodulated signals from the sine ψ signal processing channel (i.e., the signal from the compass transmitter windings which sense the field along the athwartships axis. The pitch compensating signal is combined by summation with the demodulated signal from the cos ψ channel (i.e., the signal from the compass transmitter windings which sense the field along the fore/aft axis). Since pitch angle θ and bank angle φ (as well as their trigonometric functions sin φ and sin θ) can be readily obtained from the aircraft vertical (roll and pitch) gyroscopes and dip angle D is known for any latitude and longitude, the compensating signals can be easily generated and applied to the signal processing channel coupled to the output signal processing channels from the compass transmitter to cancel vertical field error. In an alternative embodiment compensation for two cycle error is provided by generating signals proportional to the cosine of the roll angle φ and the cosine of the pitch angle θ. The two cycle compensating signals are combined with the vertical field error corrected signals from the compass transmitter by multiplication to cancel two cycle error.

Inventors

• 👤 John Edward Suminsby

Bibliographic Details