GB694419A - Adjustable potentiometer - Google Patents

Abstract

694,419. Variable resistances. SYLVANIA ELECTRIC PRODUCTS, Inc. April 6, 1950 [April 16, 1949], No. 21692/52. Divided out of 694,364. Class 37. [Also in Group XL (c)] An adjustable potentiometer comprises a planar member of relatively rigid thin sheet dielectric material having a large dielectric constant, an electrically continuous resistive element of open ring shape supported by and in engagement with one planar surface of the planar member, and a conductive member movably supported in insulated relation to at least the major length of the resistive element and capacitively coupled thereto through the intervening dielectric material. As shown in Figs. 1 and 1A, the resistance element 10 comprises an open ring of graphite &c. coated on one surface of a member 11 of material of high dielectric constant, such as titanium dioxide ceramic, titanium dioxide magnesium titanate, or titanium-zirconium dioxide ceramic. The ends of the element 10 are connected to terminals 12, 13. A conductive member or slider 20 is mounted on a shaft 24 of insulating material and is insulated from at least the major part of the length of the element 10. The member 20 includes an arm 27 which is movable along the element 10 but spaced therefrom by the dielectric member 11, which provides capacitive coupling between the arm 27 and the portion of the element 10 opposite to it. The member 20 is connected to a terminal 30. The potentiometer is adapted to be used as a volume control in a radio receiver having an intermediate frequency transformer 35, Fig. 2, a diode rectifier 38 and an audio amplifier valve 39 with an input circuit resistor 40. The capacitive coupling between the movable arm 27 and the element 10 is indicated as a condenser 32 adjustably coupled to portions of the resistance element by a slidable tap. In a modification, Fig. 3, the resistive element 10 is extended beyond the terminal 12 and the terminal 30 is bent down and connected to one end of the element by a rivet 38. The portion of the element 10 between the terminals 12, 30 may form the fixed resistor 40, Fig. 2. The portion of the resistive element 10 which lies between the terminals 12, 30 may alternatively be placed on the upper surface of the dielectric member 11, and may have a different resistance per unit length than the resistive element 10. Fig. 4 shows a dual potentiometer wherein one potentiometer comprises a resistance element 101, slider arm 20' and shaft 24<SP>1</SP>. A ring 39 of dielectric material is fixed between the element 10<SP>1</SP> and the arm 20<SP>1</SP>. The second potentiometer comprises a resistance element 40 on the opposite side of the member 11<SP>1</SP>, and an arm 41 carried by a hollow shaft 42 surrounding the shaft 24<SP>1</SP>. A ring 43 of dielectric material separates the arm 41 from the element 40. Specification 694,364 is referred to.