GB210948A - Improvements in or relating to devices for indicating magnetic directions - Google Patents

Abstract

210,948. Walker, N. Cox-, and Gill, T. H. Jan. 1, 1923. Magnetic tests and measurements.-The magnetic meridian is determined by causing the electromotive forces generated by a rotating coil in positions at right-angles to one another to affect a telephone or other frequency indicating device. The coil 2 is mounted so as to be rotatable about a vertical axis, for example by a windmill when employed on aircraft. The coil 2 is provided with a commutator 3 having two diametrically opposite segments 4. 5 which engage four brushes 6, 7 arranged 90‹ apart and connected together in pairs as shown. The brushes 6, 7 are mounted on an adjustable ring 8 having a pointer 9 co-operating with a seale 10 to indicate the setting of the brushes. A telephone 11 is connected between the pairs of brushes 6, 7. If the brush ring 8 is adjusted until one pair of opposite brushes 6, 7 is in the magnetic meridian,' the maximum electromotive force is generated in the coil 2 at the instant that the segments 4, 5, contact with this pair of brushes, and zero electromotive force is generated when the segments 4, 5 contact with the other pair of brushes 6, 7 at right angles to this position. A note. is thus obtained in the telephones of a frequency depending on the speed of rotation of the coil. If the bush ring is turned in azimuth, the electromotive force is not zero at either pair of brushes, and a note of double frequency is obtained, the determination of the meridian is effected by turning the ring 8 until a pure note of double frequency is obtained, the pointer 9 being arranged to indicate the meridian. In order to determine the direction of North, the axis of rotation of the coil is tilted in the vertical plane of the meridian and the position of minimum intensity of sound noted, which position occurs when the axis of the coil is parallel to the dip of the earth's magnetic field. The note produced in the telephones may be amplified, for exampie bv means of a thermionic valve. In a modification, the segments of the commutator may be 90‹ apart and diametrically opposite brushes connected together, or four contact segments connected in pairs may be arranged on the commutator to coact with two brushes. The apparatus may be combined with a bearing-plate, level, sextant, &c.