GB565201A - Improvements in or relating to electric measuring instruments - Google Patents

Abstract

565,201. Electromagnetic ammeters and voltmeters. SANGAMO WESTON, Ltd., and LOVEGROVE, H. J. July 3, 1943, No..10818. [Class 37] In a moving iron instrument of the radial vane type the movable vane is mounted on a pivot eccentric to the axis of the exciting coil and moves between two positions both close to the inner wall of the coil, the fixed vane being near to and parallel with the radial face of the movable vane in one limiting position while as the movable vane approaches the other limiting position the strength of magnetization of the vane increases. A spindle 2 carrying a pointer 3 is arranged to pivot about an axis which is eccentric with. respect to the axis of the coil 1. The pointer 3 moves between stops 5, 6 and in the absence of current through the coil 1 is held in the zero position by a controlling spring. The fixed vane 7 is secured to the inner wall of the coil 1, and the movable vane 8 is secured to the spindle 2. When current flows in the coil, like poles are generated at adjacent ends of the vanes, causing repulsion between them. The magnetization of the vanes is strongest at the edges of the vanes nearest the inner wall of the coil and decreases during the initial movement owing to the increasing distance between the vane and the inner surface of the coil. The magnetization reaches a minimum in the central position of the movable vane and then increases for the remainder of its movement. The result is that the scale readings at the top and bottom ends of the scale are opened up with respect to those at the centre and the scale may be made substantially linear from 10 degrees upwards.