GB553178A - Compass compensating means - Google Patents

Abstract

553,178. Magnetic compasses ; gyroscopic apparatus. BENDIX AVIATION CORPORATION. Nov. 7, 1941, No. 14397. Convention date, Nov. 29, 1940. [Classes 97 (ii) and 97 (iii)] Errors in a magnetic compass caused by the vertical component of the earth's magnetic field during turning of the craft on which the compass is mounted are compensated for by the production of an opposing magnetic field controlled in intensity in accordance with the angular movement of the craft. As shown in Fig. 1, two compensating coils 10, 11 surrounding the magnetic compass 12 are supplied with current from a battery 15. The strength of the current required to neutralize the effect of the vertical component at the latitude of the craft is obtained jointly by manual setting of a potentiometer resistor 16, 22 on an angle-of-dip scale 21 and by the automatic adjustment of a further resistor 23, 25 under the action of a rate-of-turn gyroscope 27 in which the precession angle is substantially equal to the correct angle of bank. In a modification, Fig. 2 (not shown), the angular movements of the rate-of-turn gyroscope are transmitted to the armature of a self-synchronous motor supplied from an A.C. source. The corresponding current induced in the displaced armature is fed to a second self-synchronous motor the rotor of which is set manually to the magnetic angle of dip in the locality, by the aid of a graduated scale. The current induced in the rotor according to this angular setting is led, after rectification, to one or other of two sets of compensating coils surrounding the compass, one set of coils corresponding to positions north of the equator and the other south thereof. The selection of the correct set of compensating coils is determined by a commutator simultaneously adjusted when setting the angle of dip. In a further modification, Fig. 3, the compensating field is dependent on an angle of bank indicator comprising a gyro rotor 101 constrained by a pendulum weight 106 which, at the proper angle of bank neutralizes the precessing movement during turns. Movement of a resistor 109 (similar in function to the resistor 23, Fig. 1) relative to a contact 110 causes current to flow to the compensating coils in proportion to the angle of bank and as modified by the angle of dip. The compensating field may similarly be produced under the control of a gyro vertical, Fig. 4 (not shown), or in a further modification, the compensating coils may be replaced by permanent magnets geared together to turn in opposite directions about vertical shafts.