GB797932A - Improvements in electrical indicator instruments - Google Patents

Abstract

797,932. Electrical measuring instruments. GENERAL MOTORS CORPORATION. Aug. 31, 1956 [Sept. 13, 1955], No. 26652/56. Class 37. [Also in Group XXXVIII] An instrument, particularly for use as a liquid level or temperature indicator, including a thin flat armature pivoted in a plane normal to the axes of the coils is calibrated by bending tongues integral with ductile polepieces relative to the armature. As shown, a brass or aluminium frame 10 has flanges 12, 92 between which the armature 96 is pivoted and a back wall 64 to which is attached a field piece 40 and two cores 60, 62 carrying windings 52, 54. An insulating back-plate 22 carries terminals 24, 26, an earthing plate 30 and a conducting plate 46 in contact with the terminal 26. The field piece 40 is secured to the back-plate 22 by a rivet 36 passing clear of a hole in the plate 30. The ends of the cores 60, 62 are burred over to retain the pole pieces 80, 82 in appropriately the same plane as the armature 96 ; the integral tongues of the polepieces having arcuate ends concentric with the armature. A third pole 100 is provided by an integral extension of the field piece 40 having a front edge adjacent the armature 96 and inclined to the plane of rotation. In a modification, Fig. 6, not shown, the field piece 40 has two such front edges which insect adjacent the armature 96. All the magnetic components including the armature are made of iron or other ductile, high permeability, low hysteresis material. A pointer 20 attached to the spindle 94 passes through an arcuate slot in an aluminium dial attached to the flange 12. A counterweight 98 of brass or other material is attached to the spindle 94 so that the pointer is biased towards the left-hand edge of the scale when the instrument is not energized. In a modification, Fig. 8, the polepieces have a portion of reduced thickness such as at 124. Both coils are connected in series across a battery so that the poles at 80, 82 have like polarity. The ratio of the currents and hence the direction of the. resultant field with which the armature 96 aligns is varied by a resistive transducer in parallel with the coil 54. Compensation for the temperature co-efficient of the coils is provided by a shunt 44 across the magnetic circuit of coil 54.