GB1280154A - Devices for the measurement of electric current - Google Patents

Abstract

1280154 Current measurement NEWPORT INSTRUMENTS Ltd 8 Aug 1969 [8 May 1968] 21835/68 Heading G1U An apparatus for detecting and/or measuring current comprises a movable structure incorporating two or more conductive flat strip form elements mounted to be capable of torsional displacement or oscillation, a source of current to be measured being connectible to one element and a magnetic field being established around this element. In addition, the apparatus incorporates either an electrostatic detector having one capacitor plate secured to or integral with the movable structure and stationery capacitor plates, or an electromagnetic detector arranged to sense e.m.f.s.' generated in the other element(s), to provide a capacitive variation or e.m.f. respectively representing the current in dependance on any positional displacement or oscillation of the movable structure. In one embodiment, two separate flat current conductors 10, 11 are mounted side by side and bonded to insulating strips 16, 17, the arrangement being supported between magnet poles 24, 25. The passage of current in one of the arms 10, 11 causes displacement (for D.C.) or oscillation (for A. C.) of the structure relative to the magnet poles. The displacement or oscillation may be detected by the relative capacitance changes in the plate systems 20, 10, 21 or 22, 11, 23, which are arranged in a suitable detector bridge configuration. An applied A.C. may be detected by detecting the generation of an alternating e.m.f. in a conductive path of the structure due to its oscillation between the poles 24, 25. In another electromagnetic detector system, the current carrying arm (29) Fig.5 (not shown) moves in the field due to permanent magnet poles (33, 34), while a second arm (30) moves between the poles of oppositely disposed electromagnets energized by A.C., the e.m.f. generated in the arm (30) being detected. Three arms could be used, one being between magnet poles, the others being between the poles of an electromagnet. A four pole system, with each of two arms being between the poles of separate permanent magnets Fig.4 (not shown) to increase the field strength at the arms may be used. Alternatively there may only be one conductive path through the structure, between permanent magnet poles Fig. 5 (not shown) with a metal strip insulatingly supported at a distance in the plane of the path moving between capacitor plates, to increase sensitivity. All embodiments may form part of systems in which balancing or restoring force may be applied electrostatically or electromagnetically to the moving structure, in response to detected signals, to restore the structure to its equilibrium position. The restoring force may be applied in the capacitor plate arrangements as a potential difference between the fixed and moving plates.