Patent GB-713289-A (GB)
Title: Improvements in or relating to electromagnetic apparatus
IPC: G01C19/36
Filed: 1952-07-02
Abstract: 713,289. Radio navigation. SPERRY CORPORATION. July 2, 1952 [July 2, 1951 ; July 20, 1951], No. 16665/52, Class 40 (7). [Also in Group XXXVIII] In electromagnetic devices wherein a winding is positioned in an alternating magnetic field so that the magnitude and sense of the induced EMF is indicative of its angular position relative to the direction of the field, the opposing torque due to interaction between the induced current and the magnetic field is reduced to zero by causing the induced current to be in phase with the induced EMF. Thus in Fig. 1 the rotor winding 3 of a selsyn unit 1 is made to feed into a load circuit 6 which is tuned by a condenser 7 to unity power factor. The selsyn unit may be part of a slaved gyro system, Fig. 6 (not shown), where a gyro is processed by comparison with a flux gate valve, the error signal rotating a winding whose load circuit is tuned as above to unit power factor to remove any back torque. The load circuit 16, Fig. 3, of the rotor 13 of a receiver selsyn unit 11 may also be tuned to unity power factor so that the error signal from a source 14 positions the rotor 13 without any back torque until the quadrature component is neutralized, and the in-phase component appears, amplified with respect to the input signal, in the load circuit 16. In a navigational system employing tuned rotor selsyn windings, Fig. 8, an aircraft is controlled in azimuth in accordance with the combined signals received from a radio receiver 113, determining the azimuth path, a slaved directional gyro 127 providing a heading error signal, and a gyro vertical pick-off 134, giving a bank angle signal. The DC 'signal from radio receiver 113 is fed to the rotor 116 of a moving coil instrument movement 114 with a combined DC/AC field. The resultant displacement of rotor 116 causes an AC signal proportional to this displacement to be fed, in opposition to the signal from the directional gyro 127, to a tuned coupling transformer 124 feeding rotor winding 261 of a selsyn 241, whereupon winding 261 rotates relative to the direction of the AC field supplied by stator winding 251 until the quadrature component of the signal is neutralized and the amplified in-phase component is fed via leads 132, 133 to be added to the signal from the vertical gyro 134, and a roll trim signal derived from a manually adjusted transformer 138 to displace the tuned rotor 144 of a selsyn 145, which displacement is indicated by a pointer 150, to inform the pilot, by reference to a lubber line, the required adjustment to the roll for the correct navigation path. The load circuits of the rotor windings 116, 261 are tuned to unity power factor to remove reaction torques in the displaced positions. Furthermore the phase of the added signal at each stage is such that the combined signals produce a flux in quadrature with the existing field flux in each selsyn, and thus produces no additional torque to affect the original error signal displacement. A navigational system containing both azimuth and pitch signals, Fig. 9, employing a single core 151, comprises an azimuth channel similar to that described with reference to Fig. 8 feeding one coil 172 driving the vertical needle of a cross pointer meter 173, and a pitch channel algebraically summing signals from a glide-scope receiver 131, a pitch vertical gyro 134, and a pitch trim signal manually adjusted by potentiometer 194, to feed coil 199 driving the horizontal needle of the cros pointer meter 173. The glideslope receiver may alternatively be replaced by an altimeter. Specification 690,985 is referred to.