GB418979A - Improvements in and relating to electric tachometers - Google Patents

Abstract

418,979. Electric speedometers. BENDIX AVIATION CORPORATION, 105, West Adams Street, Chicago, U.S.A. April 4, 1933, No. 10083. Convention date, April 5, 1932. [Class 106 (iii).] A disc or vane forming the indicating member is rotated against a spring control by a magnetic field energized by polyphase current supplied from a generator driven by a member, the speed of which is to be observed. The generator, Figs. 1, 4 and 5, includes a rotor driven by multiplying gear 16 from the spindle 17 and consisting of a non-magnetic block 19 carrying bar magnets 22 and I-shaped compensators 34 made of metal the permeability of which varies with temperature differently from the magnet steel. Polyphase current, the frequency of which is proportional to the speed, is generated in stationary field windings 26 connected by three wires 13 to the indicator instrument 12, shown also in Figs. 8 and 10. A non-conducting casing 38 with a metal magnetic shield 39 encloses a pair of substantially rectangular laminated cores 44, 44<a> carrying windings 45 supplied with the polyphase current, the windings being energized to the saturation point to eliminate the effect of change of voltage so that the indicator is responsive to frequency only. A thin disc 49 preferably of aluminium is mounted within gaps 47, 48 in the core on a spindle 50 carrying a pointer 56 the magnetic drag being opposed by a hair spring 54<a>. The movements of the disc are damped by a permanent horse shoe magnet 58. The disc rotates between the poles of the magnet and the keeper 59. To compensate for permeability changes in the cores 44, 44<a> resulting from temperature changes, magnetic shunts 61 are supported by spacing sleeves 62 across the gaps of the magnetic circuit. Coils 63 of fine wire may be wound on the compensators.