GB345529A - - Google Patents

Abstract

345,529. Eddy-current speedometers. DEUTA-WERKE VORM. DEUTSCHE TACHOMETERWERKE GES., 25, Oranienstrasse, Berlin. April 15, 1930, No. 11967. Convention date, April 23, 1929. [Class 106 (iii).]. An eddy-current speedometer comprises adjustable means for changing the strength of the magnetic field through the rotatable armature the deflection of which is a measure of the speed. Rotating with the shaft 1 are the C-shaped magnet 2 and soft iron core 2<1> between which is pivoted the armature 3, preferably of aluminium, which, due to the eddycurrents induced in it, rotates against the action of a spring 5 turning with it the pointer 6 fixed to the pivoted spindle 4 carrying the armature 3, to move over a scale of speeds. The device for changing the strength of the magnetic field through the armature 3 comprises a mounting 7, an adjustable ring 8 rotation of which radially adjusts the lamellµ 9 of magnetic conducting material forming an iris diaphragm to shunt an adjustable number of lines of force of the magnet 2. The ring 8 is rotatably adjusted from outside the instrument by rotating the knob 16 on the spindle 13 carrying the toothed wheel 12 gearing with the toothed sector 11 on the ring 8. A pointer 14 is fixed to the ring 8 and projects through a slot in the dial of the instrument to move over a scale. The mounting of the lamellµ is suitably made of non-paramagnetic material and the lamallµ may be lacquered in order to diminish the formation of eddy-currents in them. The C-shaped magnets can be replaced by others, e.g. shell or ring-shaped. The device can be fitted to complete instruments and is of particular use for speedometers on vehicles running on rails and driven from a vehicle wheel where the error caused by change in diameter of the wheel due to wear on the rails can be corrected by suitable opening or shutting of the lamellµ.