GB400654A - Improvements in electrical indicating instruments - Google Patents

Abstract

400,654. Current, pressure, and power meters ; frequency measurements. DRYSDALE, C. V., Derek Corner, Kingsway, Hove, Sussex. April 28, 1932, No. 12255. [Class 37.] A counter-torque device for an electrical deflectional instrument, such as an ammeter, voltmeter, frequency meter or wattmeter, comprises one or more externally-closed rings 3 of ferromagnetic material with internally-projecting poles, the moving element or the poles or both being so shaped as to give uniform periodic time for the instrument over its range of deflection. Mathematical formulae for determining the required shapes are given. In the form shown in Fig. 1, the moving element 1 is in the form of a nickel-iron or permanently magnetized cobalt-steel needle. In a modification, Fig. 3, the needle 1 is mounted obliquely on its spindle 2 in order to extend the range of deflection to about 300‹. In another form, Fig. 4, the fixed element is in the form of a permanent magnet 3 with narrow inward projecting poles, and the movable element la is in the form of cam-shaped nickel-iron stampings. The polepieces may be set obliquely, to co-operate with a pair of cam-shaped movable elements, to increase the range. An instrument for use with direct or alternating current, with deflections up to 270‹, is shown in Fig. 7, the deflecting system A being of the kind described in Specification 397,569 and mounted coaxially with the controlling system B.