GB668185A - Improvements in variable resistances - Google Patents

Abstract

668,185. Variable resistances. PRECISION DEVELOPMENTS CO., Ltd. May 3, 1950 [May 3, 1949], No. 11832/49. Class 37. A variable resistance has a helically-wound resistance winding and a plurality of electrically bonded contact elements, non-rotatable about the axis of the winding, slidable axially of the winding, rigidly connected together, and spaced around the axis of the winding so that their points of contact therewith lie in a plane normal to the axis. Fig. 1 is an end view, partly in section, and Fig. 2 is a view in the direction of the arrow II. A resistance winding 1 is wound helically upon a straight fixed former 2, parallel to which is fixed a straight contact-bar 3. Below these is a guide 4 of rectangular section having a triangular groove 6 on its lower face. An arm 8 is pivoted at 9 to a depending portion 10 of a carriage 11 which is supported on the top surface of the guide 4 by wheels 16, 18. The arm 8 carries a rotatable wheel 7 engaging one flank of the groove 6 and held in engagement therewith by a spring 17. Two wheels 13 mounted on bushes 12 on the carriage 11 engage one side of the guide 4, with which they are held in engagement by the engagement of the wheel 7 and the flank of the groove 6. An insulating terminal block 20 is mounted on an insulating plate 21 secured to the top of the carriage 11. The top of the block 20 is covered by a U-shaped metal band 22. A U-shaped insulating contact holder 23 carries on its inner surface a metal band 24 which makes contact with the band 22, the holder 23 being rigidly secured to the block 20. A contact strip 25a is formed integral with the band 22 and projects therefrom parallel to the axis of the former 2, a dimple 26a being formed near the free end and contacting with the winding 1 on the former 2. Three similar contact strips, of which two only 25b, 25c are shown, are formed integral with the metal band 24 and have corresponding dimples 26b, 26c, the points of contact of all the dimples with the winding lying in a plane normal to its axis. The four contact strips, which are electrically bonded by means of the bands 22, 24, are connected to the contact bar 3 by a contact strip 27. Owing to the wire 1 being helically wound, only one dimple engages the winding. When the carriage 11 has been moved through one quarter the pitch of the winding this dimple breaks'contact and a second dimple makes contact at a point on the winding displaced by 90 degrees, so that a change of resistance equal to one quarter the resistance of one turn can be obtained. The former 2 may alternatively be of square section. The resistance may be used as a potential divider.