GB1125685A - Improvements in or relating to variable electric resistance devices - Google Patents

Abstract

1,125,685. Variable resistors; retractive switches. HONEYWELL Inc. 28 April, 1967 [28 April, 1966], No. 19795/67. Headings H1N and H1S. A combination of an electric switching device and variable resistor comprises at least one resistive element 42, a contact (47), (Fig. 2, not shown), mounted so as to be movable along and in contact with the or either resistance element and to be movable to a rest position, as shown, where it is out of contact with the or each resistive element, a pivoted arm 22 operated by a wheel (14) for moving the contact along the or either element, and a coiled sprirg (8) biasing the contact to said rest position when not being moved. If two resistive elements 41, 42 are used, these are separated by a region covered with highly conducting material 38 and provided with a projection 48 such that in the rest position the arm 43 supporting the contact is resiliently biased away from the resistance tracks by the projection. When wheel (14) is turned, arm 22 is caused to pivot due to the forces exerted on the extrusions 27, 28 by the linkage 19, the contact (47) contacts area 38 as the arm 43 slips off projection 48, and then moves on to either resistance strip 41, 42. A reference potential is applied at 40, i.e. earth, and positive and negative potentials at opposite ends 37 of the resistive elements. The resistive elements are formed by coating arcuate members 33, of insulating material such as phenolic resin attached to the base for example by bonding, with resistive material 34 which may be a quick drying bonding agent with sintered conductive medium dispersed therein, e.g. varnish containing carbon particles. The layer 38 may be of varnish containing silver particles. Projection 48 may be of P.T.F.E., and arm 43 of phosphorbronze. Gears may be used to move the wiper arm, or it may be moved manually. An indicating scale may be included (Fig. 1, not shown).