GB610084A - Measuring system with eddy-current damping means - Google Patents

Abstract

610,084. Electrostatic meters. GES. ZUR FORDERUNG DER FORSCHUNG AUF DEM GEBIETE DER TECHNISCHEN PHYSIK AN DER EIDGENOSSISCHEN TECHNISCHEN HOCHSCHULE. Feb. 8, 1946, No. 4074. Convention date, Feb. 9, 1945. [Class 37] [Also in Group XXXII] In instruments in which a metal leaf or foil moves under the influence of electrical or mechanical forces, the leaf is arranged vertically in the space between the poles of a four-pole magnet so that its motion is damped by eddy currents. As shown in Fig. 2, a permanent magnet 1 has four inwardly-directed and inwardly tapered poles N, S. Perpendicular to the plane containing the longitudinal axis and the two poles N a thin metal foil 3 is suspended and moves under the influence of electrical or magnetic force to a position 31 during which motion the maximum change of flux through the leaf and consequent damping occurs. Fig. 3 shows a Knudsen vacuum meter in which an electrically-heated plate 5 is placed opposite the metal foil 3 and the whole is housed in an air-tight casing 6 which can be screwed by means of a flange 7 to an airtight vessel. The metal foil 3 is deflected in accordance with the degree of vacuum by impact of the gas molecules, the deflection being measured by means of a microscope 11 and prism 13. The motion is damped by eddy currents induced in the foil by the magnetic field of the four-pole magnet 1. In a modification the damping magnet is a four-pole electro-magnet arranged outside an air-tight glass casing containing the foil and heated plate. Fig. 8 shows an electrostatic meter having two movable leaves 15 suspended by means of bars 16 from a torsion thread 17. Each of the leaves 15 is situated in the magnetic field of a four-pole damping magnet 1. Fixed plates 18 are charged from a battery 19 and the potential to be measured is applied to the leaves 15.