Patent GB-177584-A (GB)
Abstract: 177,584. Field, M. B. Dec. 22, 1920. Electromagnetic current meters. -Relates to single-pivot moving-coil instruments having an approximately spherical or part-spherical core-piece, and consists in providing constructions whereby the coil may be swung into a plane transverse to the working axis, and the coil, or the coil and the filar control, withdrawn or inserted without disturbing the elements of the magnetic circuit, the control being also independent of changes of levelling. According to one construction, shown in Fig. 2, the core-piece 5 has a slot 31 to receive the pivot 11 of the coil 10 so that the coil can be swung approximately at right-angles to its working axis. The pivot rests in a jewelled cone cup 12 carried on a spring leaf 12<1>, which is given an upward set against a stiff plate 12<2> so that normally it is sufficient to carry the weight of the coil &c., but will yield when undue force is applied. A bifilar suspension 16 attached below the coil carries a load 17 anchored to a plate 18 by links 19, the plate 18 being pivoted in a bridle 25 supported by wires depending from arms 22 on a non- magnetic ring 21 positioned around the pole-pieces, Fig. 1. An upward extension 39 on the ring 21 is embraced by a forked lever 38 for setting the zero. Balance weights 26, 32 are provided, and guard wires 28, 29 prevent excessive oscillatory movements. Fig. 4 shows the coil and suspension removed, the latter being bridged by a rigid member 28<1>. Figs. 7 and 8 show an alternative construction in which a plate 50 is hinged at 51 in the horizontal plane passing through the pivot point of the coil. The lower end of the plate 50 and the load 59 on the suspension, each carry two jewel cups 57, 57 and 57<1>, 57<1>, and are held apart by struts 60. The lower arm of a bell-crank lever 58 pivoted to the plate 50, and the load 59 are also connected by a flexible tie 61, Fig. 12, the upper arm of the bellcrank lever being loaded. Guard wires 62<1> function as described above. In the construction shown in Figs. 15 and 16, a frame 75 comprising two wires clamped by insulators is carried by the filaments 74 and a third filament 76, flexible strips 77 connecting the former filaments and frame wires to the instrument terminals 72. The third filament 76 is secured in a groove in a plate 71 by a spring 80, and drops through a V notch 81. The plate 71 is attached to the ring 21. An auxiliary weight 78 forms additional loading. Figs. 39 and 42 show a construction in which the control is situated above the coil. The coil carries a cross-bar 308 between which and a drum 310 the bifilar control 309 is attached, metallic ligaments 316 connecting the coil to the terminals. The drum is mounted on a plate 313 which rotatably engages a plate 314. The plate 314 can slide vertically downwards on withdrawing the screws 315, until trunnions thereon engage clips 322, when the plate can be given a backward tilt which is limited by a projection 324. In connection with the various forms of suspension control, Specifications 175,723 and 178,789, [both in Class 106 (iv), Indicating &c.], are referred to. The surface presented by the polepieces to the core-piece may be cup-shaped, or it may be wholly cylindrical, or partly cylindrical and partly conical. The core-piece may be substantially spherical, or hemispherical, or partly cylindrical and partly conical. The core holder may be conical, tongued, or sickle-shaped. The jewel cup may be mounted on a spring-pressed plunger 114, Fig. 33, at the bottom of a conical recess in the core-piece, the pivot 11 being carried by an arm 115.