'Strapdown' induction compass transmitter with means to compensate for heading errors during turns and during dives and climbs due to the vertical component of the Earth's magnetic field and due to two cycle error

摘要

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 as well as those due to the horizontal component of the Earth's magnetic field perpendicular to the axis of tilt. Instabilities and anomalies such as "Northerly Turning Error" which are due to the vertical 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 compensating signal during turns is 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 . phi.. The vertical field pitch compensating signal while climbing or diving is proportional to the product of the sine of the pitch angle . theta., the Earth's magnetic field M and the sine of the magnetic dip angle D. These compensating signals are used to drive current through the transmitter sensing windings to produce flux which opposes and cancels the flux sensed by the compass transmitter windings due to the vertical component of the Earth's field. Compensating signals for two cycle errors due to the horizontal component of the Earth's field are proportional to cosine of the tilt angles, i.e., the roll angle &phgr; and the pitch angle &thgr; are provided to control the feedback current through the sensing windings to cancel the two cycle error.