GB1077325A - Line circuit - Google Patents

Abstract

1,077,325. Automatic exchange equipment. STANDARD TELEPHONES & CABLES Ltd. Jan. 29, 1965 [Jan. 31, 1964], No. 4034/65. Heading H4K. A subscriber's line circuit includes a line relay Lr having two windings connected to the a and b wires of the line as shown in the Figure and a cut-off relay Cr, the two relays being arranged such that depending upon their condition, i.e. operated or released, four states of line condition can be secured namely idle, off hook, line set in the dialling condition and persistent off-hook without dialling. The winding 1 of the line relay acts on a fuse for the b-wire, the a-wire being catered for by the battery fuse. When the line loop is completed by the subscriber, the line relay Lr pulls up open contacts l 1 , l 2 and by means not shown supplies a start signal to the exchange equipment which when a free first selector is found, signals by means of earth on the c-wire. The subsequent operation of the cut-off relay Cr over a path from battery 3, line relay winding 2 and cut-off relay winding I removes the line relay from the line at contacts c 1 , c 2 so setting the line in the dialling condition, but maintains the line relay energized over the above path. If no dialling is received after a predetermined time, earth is removed from the c-wire, but since the cut-off relay has a delayed release, the line relay releases first whereby the cut-off relay is maintained energized through its winding 2, the now closed contact l 2 , its made contact c 3 and the still completed line loop, to signify the persistent off-hook condition.