GB791827A - Improvements in or relating to accelerometers - Google Patents

Abstract

791,827. Electrically-operated accelerometers. MINISTER OF SUPPLY. April 22, 1949 [March 22, 1948], No. 8410/48. Class 40 (1). In an accelerometer having a mass mounted so that small movements of the mass in a given plane are used, via an electrical pick-off means, to control the magnitude of an electrical restraining force which restores the mass to its former position, and is therefore a measure of the acceleration causing the movement, the resultant force acting on the mass due to the mounting is reduced or eliminated by rotating the mass about an axis normal to the given plane and passing through the centre of gravity of the mass. The speed of rotation is adjusted so that the sinusoidal variations of the force due to the mounting do not prevent a mean value corresponding to the actual acceleration being obtained. Pick-off means employed to produce electric signals corresponding to the movements of the mass in the given plane may be inductive, capacitative, or photo-electric, the signals being amplified and used to control a restraining force, such as an electromagnetic force. In Fig. 1, which shows an elevation of one form of apparatus, Fig. 2 being a sectional plan view on the line II-II, the mass 12 is a hollow cylinder having flanges 13, 14 and 15. Three parallel fairly stiff wires 16, 17 and 18 are secured to the flange 15 at equidistant points, the lower ends being secured to a wheel 19 which is mounted by journals on the fixed pillar 22, and has teeth whereby it can be continuously rotated by the worm 23 driven by the motor 24. The upper flange 13 carries, or is constituted by, a concentric slab winding 25 which at diametrically opposite parts extends between the polepieces 26, 26a of a permanent magnet 28 on the one hand, and the segmental polepieces 29, 29a of a member 30 of magnetic material on the other. The lower flange 14 has a similar slab winding 32 which at opposite parts defining a diameter at right angles to the inter-pole parts about the winding 25, extends between further segments 33 and 34 of the member 30 and the polepieces 35 and 36 of the magnet 31. An inverted cup-like member 37 carries insulated capacitative plates 38, 39, which are linked electrically to the winding 25, and other capacitative plates 40 and 41 which cause indirect excitation of the winding 32. With the mass 12 rotating, any acceleration in a plane normal to the axis of rotation will alter the capacity between the mass and one or both pairs of plates, one or both windings then being excited and tending to make the mass 12 concentric with the pillar 22. The mean of the restraining force will be a measure of the acceleration.