Patent GB-587819-A (GB)
Title: Improvements in or relating to variable electrical resistors
IPC: H01C1/024
Filed: 1945-01-18
Abstract: 587,819. Variable contact resistances. DUBILIER CONDENSER CO. (1925), Ltd., STRAUB, E. L., and BENNETT, A. E. C. Jan. 18, 1945, Nos. 1521 and 4232. [Class 37] The hermetic sealing of a variable resistor consists of a metal casing having a closed end through which extends the adjusting spindle of the resistor and another end, closed by a sealing disc of insulating material through which the leads are carried in tubular rivets, and hermetically jointed by spinning of the rims of the casing and rivets into the disc. In one embodiment, Fig. 2, externally threaded bearing boss E is moulded into insulating disc A which supports the resistance element B, holds it rigidly inside the metal casing F, through which the boss projects at hole F<1>, by means of collar E<1> and secures the complete assembly to the panel T by nut E<2>. The resistance element B consists of a flat strip of conducting material in the form of an annulus with a break to provide two ends which are connected to leads J and J<1>. Moving contact C is pressed into contact with B and is supported by insulating arm C<1> carried by spindle D connection being made with lead J<2> through metallic annulus C<2> carried on C' spring contact C<4> on disc A and members C<5> and C<6>. An annular insulating ring G<1> lies between casing F and disc A to prevent metallic contact between the casing and the terminal tags and the joint between the edge of hole F<1> and the boss E is hermetically sealed by compressing washer G surrounding boss E, of water-resisting rubber-like material between disc A and the case F where it is countersunk as F<2>. A compressible washer not shown may also be compressed between T and F in recess F' to seal the opening in T. The adjusting spindle D is sealed in the boss E by groove D<4> which is filled with water resistant oil or grease, and annular retaining grooves D<5>, each of which is fitted with oversize washers D<6> of oil and water resistant material. An alternative method (Fig. 8, not shown) has the retaining grooves in the bush bearing E. The open end F<3> of the casing F is sealed by disc H of rubber-like material supported by disc H<1> of rigid insulating material, the two being held between the span shoulder F' and rim F<5>. Leads J<1>, J<2> and J are soldered into tubular rivets K which are sealed to the discs H and H<1> by deformation of their outer flanges into disc H or alternatively in Fig. 7 (not shown), each lead may be soldered to dished metal eyelets. In a modification of the resistance unit, Figs. 9 to 15 (not shown), the dimensions are considerably reduced by mounting the resistor element on the rigid insulating disc associated with the sealing disc as the open end of the casing. Also the bearing for the adjusting spindle is formed integral with the closed end of the casing either by making the two items separately and soldering them together or forming them in one piece by an extrusion process. Both embodiments are capable of withstanding 100‹C. at 100 per cent. relative humidity for prolonged periods. The resistor body may take any convenient form, such as those described in Specifications 431,597, 511,178 and 512,650.