GB554779A - Improvements in or relating to damping apparatus for electrical measuring instruments - Google Patents

Abstract

554,779. Magnets. SANGAMO WESTON, Ltd. (Weston Electrical Instrument Corporation). May 28, 1942, No. 7224. [Class 35] [Also in Groups XXXVI and XIX] The pointer 3 of an A.C. measuring instrument is damped by the movement of a light aluminium vane A in the air gap between bar-shaped permanent magnets 5, 6, suitably of "alnico," secured at one end within cup-shaped magnetic shields 7, 8 secured together by brackets 9 and spaced by shims 11. If the brackets are magnetic they provide a return flux-path, otherwise in cases where leakage may not be undesirable, the shields provide the return path. A soft-iron plate may replace the lower members 6, 8. The shells 13, 14 may have contacting arcuate extensions welded at 15 into a rigid whole, Fig. 5, but a soft-iron tube with transverse slot may provide an integral pair of shields, the ends being plugged by soft-iron caps carrying the magnets, Fig. 6 (not shown). Fig. 7 shows two magnets co-operating with a vane 24 of small angular extent providing damping over a full 20 degrees scale 23. The pairs of magnets may each be secured with opposite polanty within a single shell, Fig. 11 (not shown). In Fig. 12, a pair of vanes 4a, 4b, are located between end magnets and an intermediate coaxial magnet 6a in a shell 8a.