Improvements in or relating to potentiometers

891,484. Variable resistors. PLESSEY CO. Ltd. Jan. 26, 1959 [Feb. 5, 1958], No. 3766/58. Class 37. A variable resistor comprises a moulded insulating base containing a terminal having a surface flush with the surface of the base and a metallic resistive film applied over the base and the terminal surface. As shown, a metal film track 2 is deposited on a moulded carbon composition track 12 which is carried by a moulded insulating base 13. The metal film 2 may be applied by vacuum deposition, by the decomposition of nickel carbonyl or by application of a metallic paint which may be subsequently heated. Metals specified are nickel, nickel-chromium alloy, silver, gold and platinum. The track 2 may be formed through a mask or by coating the whole of the base surface and removing unwanted metal mechanically or by the etching process described in Specification 891,483. The terminals 9, 11 extend into conductive regions 5, 6 of the base 13 containing powdered carbon or silver (as described in Specification 871,995) in order to make contact with the ends of the track. Terminal 10 is connected to a metallic contact ring 7. A rotary metal brush, Fig. 1 (not shown), bridges ring 7 and the track 2. The temperature and voltage coefficients of the composite resistor are stated to approach zero. Fig. 1 (not shown) relates to a variable resistor in which the metal film 2 is deposited directly on to a moulded insulating base coated with epoxy resin or silicone varnish. Non-linear variable resistors.-The law of the component may be controlled by varying the thickness or width of the track 2 by removal of unwanted metal, by successive vacuum depositions through different masks or by variation in the composition of the alloy. Reference is made in the Provisional Specification to the reversal of the positions of the carbon and metal tracks 2, 12.