GB434446A - Improvements in or relating to telephone systems - Google Patents

Abstract

434,446. Automatic exchange systems. ERICSSON TELEPHONES, Ltd., 67, Kingsway, London, and CROWE, D. C., Ericsson Telephone Works, Beeston, Nottingham. May 30, 1934, No. 16130. [Class 40 (iv)] In a party line system, sub-stations are selected by applying different potentials to the lines, normally non- conducting devices, e.g. gas discharge tubes, being used to discriminate between the potentials applied. In addition, the polarity of the potentials may be varied to effect further selection by the use of polarized devices. In the 8-party line system shown, a relay R rectifier 22 and tube N are connected between one leg and ground at sub-stations 1-4 and between the other leg and ground at sub-stations 5 to 8 and selection is effected by applying + or - 100 volts to either leg and + or - 50 volts to the other. The selection of the line to which high voltage is applied restricts selection to sub-stations 1 to 4 or 5 to 8, the poling of the rectifiers 22 further restricts selection to a pair of substations, while the operation the two R relays to charge condensers 24 to + or - 50 volts which, on the relapse of the relays discharge over one or other of two bells 21, makes the final selection, depending on the polarity of rectifiers 23. Polarized relays and bells may be used instead of inserting rectifiers. The 100 volt supply is suitably interrupted or has superposed A.C. to provide intermittent ringing. As described, the potentials are applied over an auxiliary switch W set by an extra digit. When the final selector is set on outlet L1, L2, P relay A pulls up over the calling loop, the usual transmission bridge and ringing arrangements being omitted or, if the final selector also has access to ordinary lines, these arrangements are cut out if a level giving access to party lines is dialled. Relays B and C pull up and the additional digit is repeated to DM, the party line being opened until C falls back, whereupon the particular potentials determined by the setting of switch Ware connected to the line. Interrupters RI1 and RI2 of the usual ringing periods and rapid interrupters I1, I2 are connected in the + and - 100 volts leads. Two of the substation R relays are thus intermittently operated and one of the corresponding pair of bells 21 is pulsed by successive discharges of one of condensers 24. When the called party replies, either during a ringing or non- ringing period, slow-to-operate relay FA pulls up since the rectifier bridge 25, 26, 29, 30 provides an operating path whatever may be the polarity of the applied voltage. Relay F pulls up to complete the speaking path, the parties being fed over relays A, D. For outgoing calls, the loop extends over w1, w2 normal to the usual line circuit over X1, Y1.