GB598751A - Improvements in or relating to instruments for determining the deviation of a magnetic compass - Google Patents

Abstract

598,751. Magnetic tests and measurements. VESKIMEISTER, B. Sept. 7, 1945, No. 23170. [Class 37] An instrument for determining the deviation of a magnetic compass without swinging the ship comprises a base arranged for mounting on the compass and carrying two adjustable magnetic systems, of which one neutralizes the earth's magnetic field in the neighbourhood of the compass needle and the other constitutes an artificial magnetic meridian which can be turned about the axis of the needle. The base consists of a horizontal ring 10 having three arms 11 pivoted to it by three vertical axles 12 carrying gear-wheels 14 which mesh with a gear ring 15. This is rotatable by means of a worm 16 so as to turn the arms 11 simultaneously to vary the distance of feet 13 on the arms from the axis of the ring 10. The ring is mounted on top of a compass and the arms are adjusted until their feet engage the periphery of the compass top and locate the ring 10 with its axis coincident with that of the compass needle. A pair of sight vanes 18 at opposite ends of a diameter enable the base to be mounted with this diameter above the lubber line of the compass. A movable ring 19 is mounted on the base ring 10 and carries two standards 20 which support a tube 21 with its axis parallel to a diameter of the base. Inside the tube 21 is a right and left-handed screw 22 rotatable by a knob 23 and carrying two nuts 24 equally spaced from the axis of the base. These are attached, through a slot 25 in the tube 21, to a pair of brackets 26 mounted on the tube. Each bracket is bored to receive a split sleeve 28 in which a magnet 29 is inserted and clamped by a screw 30. These magnets are vertically over a diameter of the base, to which they present opposite poles. The strength of the horizontal component of the field due to these poles in the neighbourhood of the compass needle is adjusted by varying their distance from the centre until the earth's field is neutralized. An azimuth card 31 carries a tube 32 in which a nut 33 is slidable vertically by means of a screw 39 rotatable by a knob 40. The nut 33 is bored to take a magnet 34 extending horizontally through opposed slots 35 in the tube 32. This magnet provides an artificial magnetic meridian and strength of its horizontal component is varied by raising or lowering. The adjustment of the magnets 29 is indicated on a scale on the tube 21. The adjustment of the magnet 34 is indicated by a scale on the tube 32 and a scale on the knob 40 co-operating with an index on the tube. The permanent magnets may be replaced by electromagnets which may be similarly adjusted or means may be provided for varying the current by which they are energized or the number of turns through which the current is passed.