| 摘要 |
343,342. Regulating switches. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.- (Assignees of Whelan, D. 0.; 111, 4th Street, Scotia, New York, U.S.A.) March 10, 1930, No. 7747. Convention date, March 8, 1929. [Class 38 (v).] A variable resistance unit specially suitable for wireless circuits comprises a number of spaced contacts in the form of broken rings embedded in a mass of resistance material. In making the unit, a helix of wire 11 of phosphor-bronze or copper-nickel or other non-corrosive material may conveniently be placed in a mould into which is then packed the resistance material which may be carbon flakes with binding material such as coal tar or coal tar pitch. The unit is then heated under pressure. A longitudinal slot 15 is then cut severing the various turns of the helix, and a strip of carbon is removed so as to reveal the turns 11 which then act as contacts of the resistance unit or switch. The exterior of the unit, other than the contacts, may be coated with a protective lacquer of a pyroxylin base. |
