GB517551A - Improvements in or relating to electrical compasses for air or other craft - Google Patents

Abstract

517,551. Magnetic tests. SHEVLIN, J. T. (Siemens Apparate und Maschinen Ges.). July 29, 1938, No. 22679. [Class 37] An earth-inductor or other compass having a non-oscillating system is arranged to indicate only when it passes through the horizontal position determined by an artificial horizon, for example a gyroscopic horizon, the supports for the compass and artificial horizon being relatively fixed. An earth inductor compass 1 comprises field collectors 1a between which a coil 1b is rotated by a motor 2. The entire compass is mounted on the air or other craft at 3 and is adjustable for the required course by a wormwheel 1c, Fig. 1. An indicating instrument 4 is connected to the terminals of the coil lb through a switch 5, the parts 5a of which are fixed while the part 5b is carried by an artificial horizon 6. The switch 5 is closed only when the apparatus is in the horizontal position. The longitudinal inclination of the compass may be adjustable. The instrument 4 may give the mean value of the individual impulse, or it may be a normal voltmeter, provided with a dropping member which releases it during the closing period of the switch 5 and holds it in the last indicating position during the transmission pauses. The switches 5 may be controlled from the artificial horizon by a vane moving in a beam of light, a ray of heat, or a jet of air. Alternatively the instrument 4 may be connected directly to the earth inductor compass, the switch 5 then controlling a signal or a diaphragm covering the instrument 4 during the pauses. The whole apparatus may be oscillated in a vertical plane to render the reading independent of the period of oscillation of the craft. A modification suitable for automatic control is shown in Fig. 2, in which the moving coil 10a of the measuring instrument 10 is connected through a contact 11a of a relay 11 and through an amplifier 12 to the terminals of the earth inductor compass 1. On the spindle of the moving coil 10a is a pointer 10c and also an electrode 10d rotatable in a casing 13 filled with electrolyte between two fixed electrodes 13a, 13b. The electrodes 10d, 13a, 13b are connected to the course-controlling apparatus. The spindle of the moving coil 10a is controlled by a spring 10e and also carries an eddy-current damping device 10f, the winding 10g of which is connected to a D.C. source of current through a contact 11r of the relay 11. The winding of the relay 11 is connected through an amplifier 14 and the contacts 5a controlled by the artificial horizon 5 to a source of voltage 16. When the apparatus passes through the horizontal position the relay 11 closes the circuit of the moving coil 10a and opens the damping circuit, these operations being reversed on departure from the horizontal position. The instrument thus maintains its previous position during the pauses. In an alternative arrangement the moving coil 10a may directly control the automatic control gear, the electrodes 10d, 13a, 13b being dispensed with.