GB575340A - Improvements in or relating to variable resistances for controlling electrical potential - Google Patents

Abstract

575,340. Variable contact resistances. MILLER, G. L. March 10, 1944, No. 4452. [Class 37] In a wirewound variable resistance, the ceramic coil former is held in position on a baseplate by holders engaging it at the edge remote from the base, the holders being adjustable and capable of being clamped in position when adjusted. The baseplate 1, Figs. 1, 2, 6, is formed of moulded material, with fixing lugs 3 and a raised transverse portion 4. The ceramic coil former 6 carries two windings 18 on opposite sides, which terminate at holes 19 in the former 6, and are prevented from movement by suitable shaping of the blank portion 27 of the former 6. The latter rests upon ceramic insulating studs 28 inset in the base 1, and is held in position by holders 7. These, Fig. 5, comprise a clip portion 9 fitting over the former 6, a shank 8 and a slotted tag piece 10 which is clamped to the projecting portion 4 of the base 1 by screws 12, Figs. 1, 6, which thread into inserts 13. The ends of the windings 18 adjacent to the clips 9 are attached thereto, an extended portion 15 of the holder 7 making connexion with metal inserts 17 which carry screws 22 and form the external terminals. An additional unconnected insert and screw 21, Fig. 1, is provided as a " looping-in " terminal, the leads being brought in through a duct 25 moulded in the base 1, and protected by a cover-plate 24. Moulded into the base 1 is the pillar 30 which locates the rotatable member 31. The latter is of moulded material, and integral with the cover 32, and is held in position by the slotted collar 33 and pin 34 passing through a hole in the pillar 30. The contact member 35 has contact arms 36, Fig. 4, bearing on the windings 18, and an annular portion provided with holes 37 which engage with stud portions 38, Fig. 6, moulded into the member 31. Rotation of this member is limited by the projecting stop portion 39 which engages with a corresponding projection 5 formed in the base 1, and the apparatus is sealed by a rubber ring 40 which also serves to prevent movement of the cover 32 under vibration. The apparatus may be modified, Fig. 8 (not shown), to provide ready interchangeability of units, by extending the inserts 21 as plug members, or may be modified, Fig. 9 (not shown), to permit of mounting behind an operating panel.