GB685244A - Improvements in or relating to electrical indicating instruments - Google Patents

Abstract

685,244. Ammeters; wattmeters. GENERAL ELECTRIC CO., Ltd., and RUDGE, T. R. Oct. 18, 1951 [Oct. 11, 1950], No.. 24858/50. Class 37. [Also in Group XXXV] In an instrument indicating in dependence on the flux in a closed magnetic path at least the major part of which is formed by a ferro-magnetic core, an opening is provided in the core into which a conductor may be inserted from outside the core, the opening being bridged by a part of the core and means being provided for locating the conductor in the opening relative to the axis of the magnetic path. The ammeter shown comprises a housing 1 enclosing a moving coil meter 3 and the major part of a closed laminated core 14 of nickel-iron alloy. The core is formed with an opening 18 extending inwards for about three-quarters of the width of the core and having a flat edge 21 and a V-shaped edge 22. Two pole-pieces 23, 24 thus project from the casing and are coated with cellulose acetate. A coil 25 is wound on the core and is connected to the meter 3 through a rectifier. A conductor 26 carrying A.C. to be measured is brought into the opening 18 and pressed into the notch 22, thereby locating it so that its centre is at a predetermined distance from the magnetic axis through the core 14. An alternating flux is set up in the core 14 and the meter 3 measures the current in the conductor 26. A range-change switch by which resistances are inserted in series with the meter may be provided in the housing. An elongated electric lamp, such as a fluorescent lamp, may be passed through the central opening 27 in the core 14 so that its operating current may be measured. In a modification the core 14 may be broken at a point opposite the opening 18 to provide a gap in which the moving coil of the meter 3 may be mounted. The invention is applicable to other instruments such as wattmeters.