GB784849A - Improvements in electrical measuring instruments - Google Patents

Abstract

784,849. Moving magnet measuring instruments. ARON ELECTRICITY METER, Ltd., and RIORDAN, E. J. Oct. 2, 1952 [July 2, 1951], No. 15702/51. Class 37. [Also in Group XXXV] The eddy current damper cup 4, Fig. 10, surrounding the rotor magnet 1 is closed by a cap 7, Figs. 1 and 2, provided with four radially extending arms 7a each having a tapered positioning tongue 7b for engagement with a correspondingly located slot formed in a magnetic screen 24 or as at 18 formed in a non-magnetic sleeve 15 located within the screen 24. The spindle 2 secured to magnet 1 extends within tubes 9 and drives a pointer 60 through quadrant gear 12 and pinion 57. The deflecting coils 13 and if required ratio coils 14 are mounted on the damping chamber 4/7 so that they are supported by the arms 7a. The sleeve 15 closely embraces the coil assembly with tongues 7b fitting tightly into slots 18 and the upper end of sleeve 15 is closed by a magnetic screen plate 20 which is secured to sleeve 15 by tongues 22. The damping chamber 4/7 and tubes 9 and the surrounding sleeve 15 are all of highly conductive non-magnetic material such as copper. The zeroizing magnet 36 coaxial with rotor magnet 1 is angularly adjustable by rotating a cam eccentric 37 from screw 38 through screen cover plate 32. An adjustable magnetic shunt 41 mounted adjacent magnet 36 in the cover plate 32, Fig.. 12, controls the flux through screen 24 when the cover plate 32 is secured in position. The pinion 57 is mounted between the arms 50 of a bracket secured to a cruciform member 48, Fig. 11, which fits into notches 49 in the upper edge of screen 24 and contains the adjustable top bearing 46 for spindle 2 and is secured in position with the aid of a strip spring 61 engaging diametrically opposed slots, Figs. 7 and 8 (not shown), in the screen 24. The instrument movement is supported entirely by the dial plate 67 which is dished at 68 and has slots, Fig. 9 (not shown), engaged by lugs on the screen 24. The leads from the coils 13, 14 are taken through grommets 29 held by the cover plate 32. Reference has been directed by the Comptroller to Specification 660,894.