Patent GB-241301-A (GB)
Title: Testing arrangements for selector with self drive used in automatic or semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1924-07-22
Abstract: 241,301. Siemens Bros. & Co., Ltd., and Patterson, W. G. July 22, 1924. Automatic exchange systems.-In a group selector or rotary connector in which the hunting movement is effected by interaction between the rotary magnet and the stepping relay, a holding winding of the latter is connected to the test wiper. When an idle line is found, battery on the test terminal causes the stepping relay to, lock and prevent further operation of the rotary magnet pending the energization of the usual test and switching relay. Rotary connector, Fig. 1. Ordinary call. At the end of the first train of impulses, series relay C falls back and changeover relay E energizes over winding 1, and is held during the second train of impulses over both windings at contacts c3, e1. Relay C falls back at the end of the train and at contacts c2, c3 connects test relay G to the test wiper in parallel with winding 2 of relay E. If the wanted line is idle, relay G energizes, leeks and short-circuits relay E, which relapses slowly and connects up ringing current over ring cut-off relay F. Relay F energizes when the called subscriber replies, looks and connects up feed relay D. If the wanted line is busy, relay G fails to operate and upon relapse of relay E, ring cut-off relay F energizes over winding 1 and sends back busy tone and battery over cam contacts LF. Line relay A is thereby released, but an intermittent holding circuit is closed for release relay B over winding 2 and cam contacts LF<1>. Lamp PL is controlled by relay D and indicates release by the called subscriber. Call to a P.B.X. An additional compound wiper X<0> is provided as in Specification 203,759, and the corresponding terminals of all lines of the P.B.X. group except the last are earthed. If the first line of the group is busy, when relay C falls back, relay HS energizes over winding 1 and the leading wiper X<0>, and releases relay E, which closes a new circuit for rotary magnet RM over holding winding 2 of relay HS. The switch is advanced a step and contact rm1 is closed, so that relay E operates over both windings, locks and opens the driving circuit. Relay C relapses and closes the testing circuit. If the second line is also busy, the action is repeated, relay E acting as a stepping relay. When an idle line is found, relay E is held over winding 2 and the test wiper. If all the lines of the group are busy, relay HS releases when the last line is reached, and relay F operates and sends back a busy signal. If the number dialled corresponds to an intermediate P.B.X. line, winding 1 of relay HS is short-circuited over the two wipers X<0>, so that the line acts as an ordinary line. Dead number calls. Battery through a resistance is connected to the corresponding a terminal to operate relay F and a tone transformer is connected to the b terminal to send back a distinctive signal. First selector, Fig. 2. Release relay V connects up relay D, which closes the circuit of vertical magnet VM and sends back a dialling tone. Relay D is held during the first train of impulses at back contact a2, and then releases and connects up rotary magnet RM, relay L being energized. Contact rm1 is closed at each step to energize relav D over winding 1, winding 2 being connected over test relay T to the test wiper, so that when an idle line is found, relav D locks, and the hunting movement ceases. Test relay T energizes, locks, releases relay D by short-circuiting and connects up the line wipers. If all the lines in the level are engaged, relays D, T' energize over the eleventh test terminal, lamp PL lights over the b wiper and a busy signal may be given over the a wiper. Lamp PL also lights when the selector is first seized, and is extinguished when dialling begins.