Patent GB-690011-A (GB)
Title: Improvements in navigational compass systems
Inventor: HINE ALFRED
IPC: G01C19/36
Filed: 1951-04-13
Abstract: 690,011. Electric indicating systems. NATIONAL RESEARCH DEVELOPMENT CORPORA TION. April 13, 1951, No. 8665/51. Class 40 (i). A compass indicator is driven through an electric transmission. system by an azimuthal gyro free from precessional control, wander of the gyro being continuously detected at the indicator by a comparison fluxgate, earth inductor, or magnetic compass, the error being fed in the corrective sense to the transmission system by a mechanical or electrical differential arrangement. As shown, Fig. 1, the gyro 4 drives through a Selsyn or like transmission system 9, 10, and servo motor 12, a shaft 3b which drives through a differential 8, the shaft 3a carrying the compass card course indicator 5. A magnetic detector (not shown), e.g. an earth inductor as described in Specification 624,083, [Group XXXVI], feeds A.C. signals proportional to H cos # and H sin #, (where # is the course angle of the craft on which the detector is mounted, and H is the horizontal component of the earth's magnetic field), to a pair of sine-cosine potentiometers 2a, 2b, the arms of which are driven by shaft 3a. Normally, when the angular position of the shaft 3a corresponds to that defined by the detector, there is no output from the potentiometers. Should the gyro wander, however, the potentiometers feed an A.C. output varying in magnitude and phase sense according to the magnitude and sense of the wander, through an amplifier 6 to a torque motor 7 which. adjusts the shaft 3a to the correct position' through the differential 8. The motor 7 is made to operate slowly to prevent undue oscillation of the indicator 5. Other remote indicators may be driven from the shaft 3a, e.g. through Selsyn systems. A synchro-type of transformer may be used in lieu of the potentiometers 2a, 3a to compare the directions defined by the gyro and the magnetic detector, and the correction may, alternatively be fed into the system by rotation of the receiver stator 10. instead of by the mechanical differential, e.g. as in Fig. 2. A phase meter may be connected across motor 7 to indicate whether the gyro transmission is in alignment with the magnetic meridian. In Fig. 2 the magnetic comparator is a magnetic compass 20, the indications of which are stabilized by the azimuthal gyro 30. The known magnetic compass has an electrode system 21 on the bowl, co-acting with a semi-circular electrode 22 movable with the pivoted magnet system, and the compass liquid, e.g. alcohol and lithium chloride is electrically conductive. The electrodes are connected with resistors 23 in an A.C. fed Wheatstone bridge circuit which produces an output when the electrodes are in any position other than the symmetrical position shown. The azimuthal position of the gyro 30 is transmitted through a Selsyn transmitter 31 and manually adjustable setting control 32 to a Selsyn receiver 33, 34. Any error signal from the receiver rotor 34 is amplified at 35 and drives the compass follow-up motor 26, which would normally, i.e. if the compass were used as a master-transmitter, be driven by the amplified compass signal from the bridge, to rotate the compass bowl to restore symmetry of the electrode system 21-22 and at the same time set one or more course indicators 28 through a transmitter 27. The bridge output, in the present case, is amplified at 25 and used to drive a monitoring motor 36 to rotate the stator 33 of Selsyn receiver 33, 34, the rotor 34 of which is driven to follow the compass bowl movements by a step-by-step transmitter 29 and repeater motor 39 which may also be used to drive a further transmitter through a differential into which corrections for magnetic variation and deviation can be fed mechanically. Thus, normally the compass bowl and the rotor 34 follow changes in azimuth of the gyro-rotor axis without unbalancing of the compass bridge, the indicators 28 functioning as gyro directional indicators, but should the gyro wander, the compass bowl will follow and unbalance the bridge whereby the receiver stator 33 will be rotated to produce an output in the rotor 34 which in turn will cause the follow up motor 26 to drive the compass bowl back into alignment and at the same time adjust the indicators to compensate for the wander. The motor 36 is arranged to operate slowly, e.g. by means of a eddy current brake 40, to eliminate the effect of transient accelerations. During prolonged accelerations, the monitoring motor may be cut out automatically. A phase meter 41 connected across the motor 36 indicates whether the gyro system is aligned with the magnetic meridian.