505,506. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON. Nov. 11, 1937, No. 30998. Convention date, Nov. 14, 1936. [Class 40 (iv)] A switching arrangement comprises a number of pairs of electronic or other discharge paths U1, U2 connected in multiple to subscribers' lines AL and giving access to links FL which are also multipled to the discharge paths. According to the invention, line AL and link FL are connected over resistances rl, r2, r5, r6 to batteries E1, E2 of different voltages, the difference E1-E2 being less than the striking voltage of the paths. When subscriber A1 calls, the voltage dropped over resistances r1, r2 causes the paths to strike and busies the line, the link being busied by the voltage drop over r5, r6. Resistances shunted by condensers similar to those shown may be connected between points 5, 6 and subscribers' line to adjust the line resistance. In order to ensure that only a corresponding pair of paths shall strike, the striking voltages for different pairs may be graded, or the striking of one path U1 may bring about the striking of the other path U2. Numerical selection of a subscriber's line may be effected by application of marking potential over ML to grid electrodes with or without a change of voltage applied to the link. The line may be rung in the ordinary way or by causing the discharge tubes to oscillate.
