GB1380747A - Miniaturised potentiometers - Google Patents

Abstract

1380747 Potentiometers SOC FRANCAISE DE L'ELECTRO-RESISTANCE 4 Aug 1972 [31 Aug 1971] 36601/72 Heading HIS A rotary-contact potentiometer for use in miniaturized hybrid electric circuits comprises a metallic casing 1 containing a rotary slider 4 and its actuating member 3, and a resistor track 6 deposited on an insulating (alumina ceramic) support 5. The casing is provided with a hole 2 on one face to accept the slider-actuating member, and the opposite face is the external face of the insulating support which carries three separate metallized zones forming electrical connections and fixing the potentiometer into position. As shown, the member 3 is made by die-stamping from a sheet of, e.g. berylliumbronze coated with a noble metal and has a circular projection 19 engaging with the opening 2. A resilient tongue 28 abuts against shoulder 29 on casing 1 to prevent the control from being turned too far. The tongue yields if too much force is applied, to prevent damage. Lugs 20, 21 and 22 engage with slots 26 and 27 in the slider 4 and are bent back to hold the two pieces together. The slider 4 is larger than opening 2 so that it bears on the internal edges of the opening. It may be made of noble metal-coated beryllium bronze which after cutting-out and bending is heat treated to yield a Vickers hardness number of about 380. Support 5 has a resistor track of palladium-gold alloy screen printed on to it and tinned metallic areas 14 and 15. The external side has weldable metallic areas (7, 8, 9, Fig. 11, not shown) on it; areas (8 and 9) being contacted by terminal clips (16, 17, Figs. 8 and 9, not shown). The casing, which is of, e.g. nickel silver or gold-coated beryllium bronze, has lugs (10-13, Fig. 5, not shown) one of which bears on the internal face of the support while the others bear against metallic zone (7). The potentiometer is fixed by a remelting operation which welds the terminal clips to the support and circuit, and the support to casing and circuit. The circuit element is then ultrasonically cleaned The potentiometer is adjusted by using an insulated screwdriver in slot 23 or by means of an insulated knob added to member 3, and is then covered with an elastomeric cap.